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Treatment of Stable Chronic Demyelinating Polyneuropathy With 3,4-Diaminopyridine
ct9J
Treatment of Stable Chronic Demyelinating Polyneuropathy With 3,4-Diaminopyridine JAMES
w. RUSSELL, M.D.,* ANTHONY J. WINDEBANK, M.D., AND C. MICHEL HARPER, JR., M.D.
• Objective: To determine whether 3,4-diaminopyridine (3,4-DAP) would improve clinical or electrophysiologic function in patients with stable chronic demyelinating polyneuropathy. • Design: We conducted a prospective, randomized, placebo-controlled, blinded, crossover study of 3,4-DAP in 34 patients with demyelinating polyneuropathy. • Material and Methods: Of the 17 men and 17 women, who were 21 to 80 years of age, 27 had hereditary motor and sensory neuropathy type I and 7 had acquired demyelinating polyneuropathy. Treatment consisted of stepped doses of 3,4-DAP (increasing to 20 mg four times daily) or placebo for 4 days. Pretreatment and posttreatment determination of the Neurologic Disability Score (NDS); isometric muscle strength testing; median, ulnar, and peroneal nerve conduction studies; and measurement of serum 3,4DAP were performed. Quantitative computer-assisted sensory examinations were done in five patients. • Results: The results for the final day of treatment with 3,4-DAP or placebo and the differences between Improved treatment for acquired demyelinating neuropathies, such as chronic inflammatory demyelinating neuropathy and multifocal motor neuropathy with conduction block, has become available during the past decade. Currently, no effective therapy is available for hereditary demyelinating neuropathies, such as hereditary motor and sensory neuropathy (HMSN) type 1. Patients who receive immune-modulating treatment for inflammatory demyelinating neuropathies frequently have chronic disability.!? therefore, a need exists for symptomatic therapy. From the Department of Neurology, Mayo Clinic Rochester, Rochester, Minnesota. *Current address: National Institute of Neurological and Communicative Disorders and Stroke, National Institutes of Health, Bethesda, Maryland. This study was supported in part by Grant FD-R-000664 (ROl) from the Food and Drug Administration and Grant RR 00585 from the National Institutes of Health, Public Health Service. Address reprint requests to Dr. A. J. Windebank, Department of Neurology, Mayo Clinic Rochester, 200 First Street SW, Rochester, MN 55905. Mayo Clin Proc 1995; 70:532-539
pretreatment and posttreatment findings for total NDS, sensory NDS, isometric muscle strength testing, compound muscle action potential amplitude, sensory nerve action potential amplitude, motor and sensory conduction velocities, and vibration and cold detection thresholds did not vary significantly. A small improvement of 4 points in the motor NDS (P<0.05) was found. Five patients with electrophysiologic conduction block had no significant reduction in the degree of block. • Conclusion: Because no improvement was noted in most measurements of neurologic function, despite use of high doses of drug, 3,4-DAP is unlikely to be beneficial in the treatment of stable chronic demyelinating polyneuropathy. (Mayo Clin Proc 1995; 70:532-539) 4-AP = 4-aminopyridine; CIDP = chronic inflammatory demyelinating polyneuropathy; CMAP = compound muscle action potential; 3,4-DAP = 3,4-diaminopyridine; HMSN =hereditary motor and sensory neuropathy; IMT = isometric muscle strength testing; NCS =nerve conduction studies; NDS =Neurologic Disability Score; SNAP =sensory nerve action potential
In the normal myelinated axon, voltage-sensitive sodium channels are densely clustered (approximately l,OOO/J..lm2) in the axonal membrane at the node of Ranvier'v and at a lower density (approximately 25/J..lm2) in the internodal axonal membrane," whereas fast K+ channels, sensitive to 4aminopyridine (4-AP), are present under myelin in the internodal or paranodal region.v' These K+ channels are thought to assist in the generation of internodal resting potential," to prevent reexcitation, and to stabilize firing properties after the action potential." In regions of paranodal and internodal demyelination, saltatory action potential propagation is inhibited and may become physiologically blocked. As fast K+ channels become exposed, repolarization is impaired. The net effect is slowing of conduction of the action potential and delayed repolarization. In animal studies, certain aminopyridines are able to block the fast K+ channels and are able to improve conduction in regions of nerve demyelination. 10,11 Aminopyridines such as 4-AP have no effect on the action potential waveform or firing properties of mature 532
© 1995 Mayo Foundation for Medical Education and Research
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Mayo Clio Proc, June 1995, Vol 70
myelinated axons, but they do increase the duration and amplitude of the compound action potential in unmyelinated and regenerating myelinated fibers.v" When internodal demyelination occurs, exposure of fast K+ channels holds the axonal membrane close to the potassium equilibrium potential. Blockage of these channels by 4-AP improves the conduction safety factor" and may result in restoration of conduction and reduction of conduction block.":" In addition to these effects on the axonal membrane, aminopyridines enhance neurotransmission at the neuromuscular junction in both animal models'"-" and humans.v-" The observed effects in the demyelinated axon have led to therapeutic trials with aminopyridines in multiple sclerosis. Some studies have shown small improvements in neurologic function and visual evoked response latencies,":" but improvement has not been uniformly observed." Increasing the release of acetylcholine at the neuromuscular junction has been shown to be beneficial in the treatment of LambertEaton myasthenic syndrome,"> type A botulism," and certain variants of congenital myasthenia." Although studies in animal models of demyelinating neuropathy seem promising, no controlled trial of 3,4diaminopyridine (3,4-DAP) in human neuropathy has been previously conducted. In the current study, subjects who had stable demyelinating neuropathy were entered in a doubleblind, placebo-controlled, crossover trial and treated with 3,4-DAP to determine whether clinical or electrophysiologic function would improve. METHODS
Selection ofPatients.-Patients 20 to 80 years of age were eligible for inclusion in the study. All patients underwent a complete clinical examination, electrophysiologic study, supportive blood tests, and, when necessary, cerebrospinal fluid examination and nerve biopsy at Mayo Clinic Rochester to determine eligibility. In order to avoid improvement or decline in function due to the natural history of the disease, only patients with a stable demyelinating neuropathy, defined as a stable clinical condition for at least 6 months before entry in the study, were eligible to participate. Eligible patients had one of three clinical diagnoses: HMSN type I, chronic inflammatory demyelinating polyneuropathy (ClDP), or multifocal motor neuropathy and conduction block. Patients were excluded from analysis if their neuropathy could have been partially or wholly due to a disorder other than these three clinical conditions or if any other medical condition existed that might have affected the neuropathy or evaluation during the trial. Patients with a predisposition to seizures or to cardiac, hepatic, or renal disease were excluded from the study. The diagnosis of HMSN type I was based on the clinical and genetic history, examination, electrophysiologic studies, and, when appro-
3,4-DIAMINOPYRIDINE IN DEMYELINATING NEUROPATHY
533
priate, sural nerve pathologic findings and genetic tests, with application of criteria previously described by Dyck and associates." Patients diagnosed with chronic inflammatory demyelinating neuropathy fulfilled the research criteria of the American Academy of Neurology AIDS Task Force." Subjects were diagnosed as having multifocal motor neuropathy and conduction block if they had an asymmetric motor neuropathy, electrophysiologic conduction block (see subsequent material), and other supportive clinical and laboratory findings, including increased levels of antibodies to GMl,3° Patients treated with immunosuppressive agents had no change in dosage for at least 6 months before entry into the study. Study Design.-3,4-DAP was obtained in powder form from Regis Chemical Company (Morton Grove, Illinois). The powder was formulated with lactose into 5-mg capsules. Placebo capsules were formulated from lactose. Four serum samples were obtained from each patient-before the trial was begun, after the washout period, and after a 20-mg dose of placebo or 3,4-DAP had been taken on the final day of each phase of the crossover trial. Serum levels of 3,4-DAP reach a peak after 60 minutes and then decay during a period of 1 to 200 minutes; thus, the medication could be administered four times a day. Blood specimens were obtained in the morning I hour after the administration of 3,4-DAP or placebo. Protocol.-The study protocol was approved by the Mayo Clinic Institutional Review Board, and written informed consent was obtained from each participant. Patients were admitted to the General Clinical Research Center during treatment. The study was designed as a double-blind, crossover trial. Subjects who enrolled in the study were treated with either 3,4-DAP (active treatment) or placebo during an initial phase that lasted 4 days, followed by a washout period of at least 5 days, during which they received neither placebo nor 3,4-DAP. After the washout period, subjects entered the crossover phase, during which they received 4 days of treatment with whichever medication (3,4-DAP or placebo) had not been administered initially. For randomization to 3,4-DAP or placebo during the initial phase, a random number system generated by the Mayo Clinic Pharmacy was used. Medication was coded by the pharmacy, and only the study pharmacist was aware of the code. Nursing staff ensured that all medication was taken by the subjects, and empty containers were cross-checked by the pharmacy. The initial dosage was 5 mg of 3,4-DAP or placebo, four times a day for the first day; the dosage was doubled on the second and third days and then kept at 20 mg four times a day for the fourth day. A Neurologic Disability Score (NOS) was determined before the initial and crossover phases were begun, after treatment, and daily while medication was administered. Isometric muscle strength testing,
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3,4-DIAMINOPYRIDINE IN DEMYELINATING NEUROPATHY
electrophysiologic studies, and sensory testing were performed before subjects entered the study and on the fourth (last) day of each phase of the trial; the tests were done at similar times of the day and with use of identical techniques. These tests were performed within I to 2 hours after the subjects took the test drug, for reflection of an optimal medication effect. Venipuncture for serum electrolytes, complete blood cell count, and 3,4-DAP level was performed before each phase of the crossover trial and on the fourth (last) day of each phase. Each patient completed a daily medication adverse effect report, with the assistance of the nursing staff. In order to avoid unblinding the examining physician, patients were asked to report any major adverse medication effects to a physician who was not participating in the study. NDS and Biomechanical Evaluation.-Results of a neurologic examination were graded by using a previously established scoring system (the NDS);31,32 this assessment was performed by a single blinded examiner to avoid interexaminer variability. With use of this system, strength was graded against normal expectations for the patient's age and sex. The range of scores was as follows: 0 = normal strength; I = mild weakness (25% weaker than normal); 2 = moderate weakness (50%); 3 = severe weakness (75%); and 4 = unable to generate any force (100%). When necessary, subclassifications of weakness (for example, 3.25, 3.5, and 3.75) were allowed. Muscle stretch reflexes were graded as follows: normal =0; decreased = 1; and absent = 2. Sensation (touch-pressure, pinprick, vibration, and joint position sense) was assessed on the dorsum of the index finger and great toe (near the base of the nail) and was graded as follows: normal = 0; decreased = 1; and absent = 2. This system has been shown to be reproducible and to have low intraobserver variability, particularly for total NDS and weakness NDS.32 Worsening neurologic function is indicated by an increase in the NDS. The total NDS was further subdivided into a motor NDS (strength evaluation only) and a sensory NDS (sensory determinations only). Findings were compared between 3,4-DAP and placebo phases by using mean summated NDS (total, motor, and sensory) and mean delta NDS (difference between NDS before and after treatment). Biomechanical Isometric Strength Evaluation.-Biomechanical isometric muscle strength testing (IMT) was done bilaterally for the following functions: elbow flexion, wrist flexion, thumb abduction, index finger abduction, key pinch, knee extension, and ankle extension. All studies were performed by one of two physical therapists. The maximal isometric force (best of three trials) was measured for each determination. Measurements (in kilograms per centimeter) were made bilaterally, corrected when necessary for dominance, and expressed as percent of normal. Data were com-
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pared by using mean summated biomechanics scores (for all muscles tested, the proximal muscles, and the distal muscles) and delta scores (difference between scores after medication and at baseline). Electrophysiologic and Sensory Threshold Studies.Standard techniques" were used for nerve conduction studies (NCS), and care was exercised to use identical placement of electrodes and to maintain limb temperature at or above 32°C by using surface thermistors and infrared lamps. When necessary, the limbs were immersed in warm water for 15 minutes at 38°C. Distal median, ulnar, and peroneal compound muscle action potential (CMAP), median and ulnar sensory nerve action potential (SNAP), and motor and sensory conduction velocities were determined, Comparisons between placebo and active phase NCS were made by using mean summated CMAPs (sum of median and ulnar CMAPs), summated SNAPs (sum of median and ulnar SNAPs), summated motor conduction velocities (sum of median and ulnar motor velocities), summated sensory conduction velocities (sum of median and ulnar sensory velocities), delta NCS (difference between NCS value after 3,4-DAP phase [or placebo phase] and baseline value), and individual nerve measurements. The use and validity of summated nerve and muscle action potential and conduction velocity data for detection of change have been extensively discussed.P-" For determining the presence of conduction block, the following requirements were met: a supramaximal stimulus was used and the amplitude and the negative peak CMAP area were reduced 50% or more with proximal stimulation, in the absence of dispersion, along long nerve segments normally unaffected by compression palsies. Cold and vibration detection thresholds were measured on the dorsum of the foot and toe, respectively, with use of the computer-assisted sensory examination IV device." Results were obtained by using a forced-choice method'<" and expressed as deviations from normal for age, site, and sex. Sensory detection thresholds, while subjects were in the active and placebo phases, were compared by using mean summated normal deviates for cold or vibration and mean delta normal deviates (difference between baseline and postmedication results). Statistical Analysis.-Quantitative measures of function with 3,4-DAP or placebo were compared by using Student's t test for paired values or the nonparametric Wilcoxon signed rank test for data that were not normally distributed. The Pearson correlation coefficient was used to determine the association between the serum level of 3,4-DAP and measures of neurologic function. Statistical significance was defined as a P value of less than 0.05. For ease of comparison of data, results were expressed as mean ± standard error of the mean.
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3,4-DIAMINOPYRIDINE IN DEMYELINATING NEUROPATHY
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RESULTS Thirty-four patients with stable chronic demyelinating polyneuropathy entered the protocol, and all patients completed the initial and crossover phases of the study. The 34 patients (17 men and 17 women) ranged in age from 21 to 80 year s (mean, 48); 2 patients were Hispanic and 1 was AfroAmerican. Of the 34 patients, 27 had stable HMSN type I, 5 had multifocal motor neuropathy and conduction block, and 2 had CIDP with no electrophysiologic conduction block. Neurologic Disability Score.-In the 34 study patients, the NDS was determined before and after each arm of the crossover triaL No significant difference was noted in the mean total NDS at the start of the placebo phase (72.3 ± 5.7) and at the start of the active phase (73.2 ± 5.6) or between the total NDS at the start (72.3 ± 5.7) and the end (68.2 ± 5.8) of the placebo phase. The mean delta total NDS (difference between total NDS at start and end of each phase) for the 3,4DAP arm of the trial was not significantly different from that for the placebo phase (Table 1). Only four patients had a mild increase in total NDS ; the total NDS in the rest remained unchanged or showed a mild decrease. The motor component of the NDS increased from baseline while patients were receiving 3,4-DAP. In comparison with placebo, a 4-point improvement was detected in the mean delta motor NDS while subjects were taking the drug (P<0.05); however, the difference between the mean motor NDS for active (40.87 ± 4.26) and placebo (44.33 ± 5.43) groups at the end
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of each treatment arm did not reach significance (P = 0.051 ). No difference was observed in the mean delta sensory NDS , or other measures of sensory NDS, between subje cts during the active phase and the placebo phase of the stud y. In patients with multifocal motor neuropathy or CIDP, no statistical difference was noted in mean delta total NDS, motor NDS , or sensory NDS after the 3,4- DAP triaL
Biomechanical Isometric Strength Evaluation.-Mean values from biomechanical IMT were determined in 34 patients. Altho ugh the mean IMT score increased slightly after the active phase (51.04 ± 3.97) in comparison with the placebo phase of the study (50.20 ± 4.29) , the difference did not reach significance. Delta IMT results for active (5.60 ± 1.65) and placebo (4.60 ± 0.94) phases of the trial were not significantly different. When IMT scores for proximal and distal muscles were con sidered separately, no significant difference in results was noted after 3,4-DAP or placebo phases. In patients with multifocal motor neuropathy or CIDP, no significant difference was found in mean delta IMT results after treatment with 3,4-DAP. Electrophysiologic Studies.-Median and ulnar nerve conduction studies were performed in 34 subjects and peroneal studies in 22. Summated CMAP amplitudes (sum of ulnar and median CMAP amplitudes) were determined in 32 patients; both CMAP amplitudes were unrecordable in 2 patients. Summated SNAP amplitudes could be recorded in only 13 patients. The mean delta summated CMAP ampli-
Table 1.-8umma ry of Neurologic Endpoints in Study Subjects With Stable Chronic Demyelinating Polyneuro pathy* Determination
No.t
~Active*
~Placebo§
Significance
TotalNOSf Motor NOS SensoryNOS Biomechanics LCMAP(mV) LSNAP(J1V) Peroneal CMAP (mV) LMCV (rn/s) LSCV (m/s) Vibration Cold detection
34 34 34 34 32 13 8 31 10 5 5
7.20± 1.59 5.61 ± 1.49 1.56± 0.38 5.60 ± 1.65 0.22 ± 0.19 1.57± 2.30 0.02 ±0.15 0.74 ± 0.75 14.10± 9.04 0.06 ±0.08 0.23 ±0.20
4.39 ± 1.21 0.81 ± 1.84 1.12±0.40 4.60±0.94 0.17 ± 0.38 1.35± 1.58 0.31 ±0.15 1.01 ± 1.03 7.20±7.23 0.1O±0.06 0.01 ± 0.10
NS P<0.05 NS NS NS NS NS NS NS NS NS
*Results are recorded as mean ± standard error of the mean. LCMAP = summated compoundmuscle action potentialamplitude for median and ulnar nerves; LMCV = summated motor conduction velocity for ulnar and median nerves; NOS = Neurologic Disability Score; NS = not statistically significant; LSCV = summated sensory conductionvelocityfor ulnar and mediannerves; LSNAP = summatedsensory nerve action potential amplitude for ulnar and median nerves. [Number of patients in whom a result could be obtained. *Result on final day of 3,4-diaminopyridine phase of crossoverstudy- result immediately before drug trial was initiated. §Resulton final day of placebo phase of crossover study - result immediately before placebo phase was begun. #Total NOS = combineddata from the motor NOS, sensory NOS, and reflex NOS.
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3,4-DIAMINOPYRIDINE IN DEMYELINATING NEUROPATHY
tude and mean delta summated SNAP amplitude were similar in subjects during the 3,4-DAP and the placebo phases of the study (Table I). The mean summated CMAP amplitude (6.24 ± 0.87 mV) and mean summated SNAP amplitude (27.28 ± 9.99 flV) after treatment with 3,4-DAP were not significantly different from the summated CMAP amplitude (6.30 ± 0.91 mY) and summated SNAP amplitude (27.42 ± 11.76 flV) after placebo. Mean CMAP amplitude for the ulnar and median nerves, separately, remained unchanged after treatment with 3,4-DAP. Peroneal CMAP amplitudes could be recorded in only eight subjects. The mean delta summated CMAP amplitude for each phase of the trial and the mean summated CMAP amplitude after 3,4-DAP treatment (0.57 ± 0.19 mY) did not vary significantly from the result after the placebo phase (0.71 ± 0.23 mY). Ulnar and median forearm segment motor conduction velocities could be recorded in 31 patients and sensory conduction velocities in 10. Mean delta summated motor and sensory conduction velocities did not vary significantly after 3,4-DAP treatment (Table I). After treatment with 3,4-DAP, the mean summated motor conduction velocity (49.94 ± 4.07 m/s) and the mean summated sensory conduction velocity (95.0 ± 10.47 m/s) did not vary significantly from the mean summated motor conduction velocity (50.23 ± 3.92 m/s) and the mean summated sensory conduction velocity (88.7 ± 14.42 m/s) after placebo. Considered separately, mean median and ulnar forearm motor and sensory conduction velocities were not significantly altered after 3,4-DAP treatment. Peroneal conduction velocities were unrecordable in most patients. Patients with multifocal motor neuropathy and conduction block or those with CIDP, when considered separately from the group with HMSN type I, showed no significant improvement in any electrophysiologic variable. In patients with multifocal motor neuropathy, partial or complete electrophysiologic conduction block was present in a total of six ulnar or median nerves. The mean percentage reduction in negative peak CMAP area (percentage conduction block) at baseline was 68.5 ± 7.3% for these nerves. The mean percentage conduction block was 72.3 ± 6.6% after treatment with 3,4-DAP and 69.8 ± 8.0% after administration of placebo. No significant improvement was found in the mean percentage conduction block for all affected nerves or in individual nerves after administration of 3,4-DAP. Sensory Detection Thresholds.- Vibration and cold detection thresholds were measured on the dorsal aspect of the foot in five patients, and results were expressed as normal deviates (Table I). The mean delta cold and vibration detection thresholds did not differ significantly when subjects were taking 3,4-DAP or placebo, although slight decreases were noted during the active medication phase. After 3,4DAP treatment, the mean normal deviate for cold detection
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was 1.77 ± 0.4 and for vibration detection was 2.11 ± 1.2, in comparison with 2.02 ± 0.18 for cold detection and 2.14 ± 0.1 for vibration detection after placebo. Medication Levels and Side Effects.-Serum samples were obtained in 33 patients. No significant change in serum electrolytes or complete blood cell count was observed during the trial in any patient. As expected, the 3,4-DAP level was unrecordable in all subjects before entrance into the trial, after the washout period, and after the placebo phase. The mean level I hour after taking 20 mg of 3,4-DAP was 54.86 ± 5.85 ng/mL. Although mean 3,4-DAP levels were higher in women (58.82 ± 8.93 ng/mL) than in men (47.67 ± 4.76 ng/mL), they were not statistically significantly different. No association was found between the serum level of 3,4-DAP and mean delta total NDS, mean delta motor NDS, mean delta sensory NDS, mean delta summated CMAP amplitude, mean delta summated SNAP amplitude, mean delta summated motor conduction velocity, or mean delta summated sensory conduction velocity. For a 4-day treatment period, adverse effects were mild, and all patients were able to tolerate the full dose of 3,4-DAP. One patient, in whom light-headedness developed, requested a reduced dose of medication. The subject was found to be taking placebo at the end of the study and had not had postural symptoms during the 3,4-DAP phase of the trial. Four subjects (12%) had no adverse symptoms during 3,4-DAP treatment. The most common symptom related to use of medication was facial (predominantly perioral) paresthesia (Table 2). This symptom was most likely to occur when the subject was taking 80 mg/day. Most side effects developed within 1 hour after the medication was taken and were transient. Generalized muscle fatigue was infrequent but more persistent. Although fluctuations occurred in determinations of motor and sensory function, 3,4DAP did not cause significant deterioration in any of these measurements. Most adverse symptoms subsided as the subjects continued to take the medication. No patients had seizures or syncope; however, mild postural lightheadedness developed in 35% of subjects taking 3,4-DAP. Less frequently recorded adverse effects were insomnia (15%), transient urinary frequency (12%), increased tearing or nasal discharge (6%), increased sweating (6%), transient facial flushing (6%), transient hand tremor or muscle twitching (6%), headache (6%), and transient parageusia (3%). DISCUSSION The aminopyridines have been shown to affect potassium channels and the generated action potential in both myelinated and nonmyelinated axons.ll.36-38 Aminopyridine-sensitive potassium channels seem to be similar in their pharmacologic properties in many species, ranging from the squid axon":" and cockroach giant axon? to mammalian
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Table 2.-Frequency and Duration of Side Effects During a Controlled Trial With 3,4-Diaminopyridine in 34 Patients With Stable Chronic Demyelinating Polyneuropathy Patients
Time (min) to onset of symptom
Duration
Adverse effect
No.
%
Mean
Range
Mean
Range
Facial paresthesia Postural light-headedness Paresthesia of hands or feet Muscle fatigue Nausea, abdominal discomfort, vomiting
24 12
71 35
50 48
10-120 20-60
45 min 4h
10-90 min 10 min-24h
11
10
32 29
60 50
20-120 30-75
40 min 18 h
15-90 min 1-24 h
6
18
55
15-75
9h
fibers. 1O,14,ls Although 4-AP has been shown to improve nerve conduction in demyelinated or regenerating axons in animal studies,9,10,14-16 in one human study no significant change in conduction block or clinical improvement was observed in six patients with inflammatory demyelinating neuropathies treated with 3,4-DAP. 43 Penetration of 3,4DAP into the cerebrospinal fluid is significantly less than for 4-AP. In animal studies, intracisternal injection of both drugs results in an equal frequency of occurrence of seizures; therefore, the poor penetration probably accounts for the fewer observed seizures with 3,4-DAP.44 The potassium channel blocking capacity of 3,4-DAP in comparison with 4AP varies in different animals but is greater in the squid giant axon (Loligo pea/ei) and the cockroach axon. 39,4S For these reasons, subjects were treated with 3,4-DAP rather than 4AP in this study. In the current study, 27 patients had a hereditary neuropathy with demyelinating features (HMSN type I), 2 had stable CIDP, and 5 had stable multifocal motor neuropathy and conduction block. Despite clear evidence of demyelination, no overall improvement was observed on the clinical examination, IMT, or motor conduction studies. Although the motor component of the NDS score slightly improved during administration of 3,4-DAP, this finding was not supported by the IMT. A decrease of 4 points in the motor NDS would correspond to a 25% increase of muscle strength in two muscle groups bilaterally. A change of 2 points is the minimal detectable alteration in neurologic functionr'v" however, a change of 4 points is a very minor clinical adjustment. In animal studies, 3,4-DAP has been shown to increase the quantal release of acetylcholine at the neuromuscular junction'v" after potentiation of calcium influx through voltage-gated calcium channels," and it may act directly on muscle fibers to increase twitch amplitude." Although this mechanism may explain the improvement in the motor NDS, an increase in CMAP amplitude is observed when disorders of neuromuscular transmission are treated with 3,4_DAP.19,27 We found no statistically significant in-
30 min-24h
crease in any measure of CMAP amplitude during the 3,4DAP phase in comparison with placebo. Our previous pharmacokinetic studies of treatment with 3,4-DAP in subjects with Lambert-Eaton myasthenic syndrome indicated that the peak serum concentration of drug would occur approximately 1 hour after oral administration, and results of clinical, electrophysiologic, and IMT were most improved I to 3 hours after the drug was administered (unpublished data). The electrophysiologic studies were performed on the last day of treatment, concurrent with the expected peak serum concentration of 3,4-DAP. Most likely, any positive effect by 3,4-DAP on the electrophysiologic studies would be noted at this time. The dosage of 3,4-DAP used (up to 80 mg/day) should have been adequate to elicit a response because most patients with neuromuscular transmission defects demonstrate improvement with this dose,'? and studies in patients with multiple sclerosis have shown that those who respond to 4-AP do so at doses of less than 55 mg/day.22,23,sl Furthermore, in our study, even though absorption of 3,4DAP may have been variable after oral dosing, no correlation existed between 3,4-DAP serum levels and clinical and electrophysiologic measures. In the five subjects with conduction block, no significant change in the electrophysiologic findings was observed, and either no or minimal clinical improvement was noted. This outcome was similar to the findings in six patients who had electrophysiologic evidence of conduction block-four with Guillain-Barre syndrome and two with CIDP.43 No statistically significant improvement was found in determinants of sensory function, including clinical assessment, sensory conduction studies, or measures of thermal and vibratory thresholds, with use of computer-assisted sensory examinations. This result suggests that 3,4-DAP had little effect on sensory myelinated fibers. Cold sensation activates predominantly thinly myelinated and, less frequently, unmyelinated fibers in primates and humans.v" In this study, however, afferent unmyelinated axons, such as those from polymodal nociceptors, or autonomic fibers,
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3,4-DIAMINOPYRIDINE IN DEMYELINATING NEUROPATHY
which may be responsive to 3,4_DAP,19,40,55 were not specifically tested. The most frequently observed adverse effect of 3,4-DAP was a mild facial (predominantly perioral) tingling sensation, which was noted by 71 % of our patients. Most adverse effects developed within 1 hour after administration of 3,4DAP and generally dissipated within 24 hours, while the same or a higher dose of the medication was maintained. Despite the range of symptoms, all patients completed the study without a reduction in the final dose of 3,4-DAP. No clinical seizures developed in any patient. The serum levels of 3,4-DAP varied considerably, a finding previously observed with 4-AP as well." The lack of correlation between the serum 3,4-DAP level and any measure of neurologic improvement suggests that the variability in serum level did not adversely affect the results of the study. Why a discrepancy would exist in the results of aminopyridine treatment between demyelinated and regenerating mammalian fibers and this human study of demyelinating neuropathy is unclear. In the animal studies, however, demyelinating lesions were usually studied in acute or subacute conditions;9,lO,14,15 perhaps the distribution and sensitivity of fast conducting potassium channels differ in the chronic demyelinating neuropathy we studied. This explanation would not clarify the lack of efficacy in subjects with Guillain-Barre syndrome described by Bergin and colleagues," although no pharmacokinetic data were available in that study and whether the serum levels were adequate is unknown. When long-term follow-up studies have been performed in animal nerves after crush injury, sensitivity to aminopyridines has progressively declined." This result may have been due to secondary axonal changes. In animal studies with aminopyridines, extremely sensitive isolated nerve preparations have usually been used to record action potentials, but the correlation of these electrophysiologic changes with improvement in function has not been specifically examined. Another possibility is that the molecular characteristics of fast potassium channels in human peripheral nerves vary from those in other mammals and may be less sensitive to aminopyridines. Whatever the reason for the difference, this study indicates that 3,4-DAP produces no clinically significant improvement in neurologic function in subjects with chronic stable demyelinating polyneuropathy.
ACKNOWLEDGMENT The secretarial assistance of Linda A. Goldbeck is greatly appreciated. REFERENCES 1. Dyck PJ, O'Brien PC, Oviatt KF, Dinapoli RP, Daube JR, Bartleson JD, et a1. Prednisone improves chronic inflammatory demyelinating polyradiculoneuropathy more than no treatment. Ann Neurol 1982; 11:136-141
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DyckPJ,DaubeJ,O'BrienP,PinedaA,LowPA, Windebank AJ, et a1. Plasma exchange in chronic inflammatory demyelinating polyradiculoneuropathy. N Engl J Med 1986; 314:461-465 Cornblath DR, Chaudhry V, Griffin JW. Treatment of chronicinflammatorydemyelinatingpolyneuropathy withintravenous immunoglobulin. Ann Neurol 1991; 30:104-106 Pellegrino RG, Ritchie JM. Sodium channels in the axolemma of normal and degenerating rabbit optic nerve. Proc R Soc Lond B BioI Sci 1984; 222:155-160 Waxman SG, Ritchie JM. Molecular dissection of the myelinated axon. Ann Neurol 1993; 33:121-136 Ritchie JM, Rogart RB. Density of sodium channels in mammalian myelinatednerve fibers and nature of the axonal membrane under the myelin sheath. Proc Natl Acad Sci U S A 1977;74:211-215 Chiu SY, Ritchie JM. Potassium channels in nodal and internodal axonal membrane of mammalian myelinated fibres. Nature 1980;284:170-171 Chiu SY, Ritchie JM. On the physiologicalrole of internodal potassium channels and the security of conduction in myelinated nerve fibres. Proc R Soc Lond B Biol Sci 1984; 220:415-422 Kocsis JD, Waxman SG, HildebrandC, Ruiz JA. Regenerating mammalian nerve fibres: changes in action potential waveform and firing characteristics following blockage of potassium conductance. Proc R Soc Lond B Biol Sci 1982; 217:77-87 Ritchie JM. Sodium and potassium channels in regenerating and developing mammalian myelinated nerves. Proc R Soc Lond 1982;215:273-287 Baker M, Bostock H, Grafe P, Martius P. Function and distribution of three types of rectifying channel in rat spinal root myelinatedaxons. J Physiol 1987;383:45-67 Kocsis JD, WaxmanSG. Long-termregeneratednerve fibres retain sensitivity to potassium channel blocking agents. Nature 1983; 304:640-642 Waxman SG. Demyelinationin spinal cord injury. J Neurol Sci 1989;91:1-14 Sherratt RM, Bostock H, Sears TA. Effects of 4aminopyridine on normal and demyelinated mammalian nerve fibres. Nature 1980; 283:570-572 Targ EF, Kocsis JD. 4-Aminopyridineleads to restoration of conduction in demyelinated rat sciatic nerve. Brain Res 1985; 328:358-361 Targ EF, Kocsis JD. Action potential characteristics of demyelinated rat sciatic nerve following application of 4aminopyridine. Brain Res 1986;363:1-9 Braga MF, Harvey AL, Rowan EG. Effects of tacrine, velnacrine (HP029), suronacrine (HP128), and 3,4diaminopyridine on skeletal neuromuscular transmission in vitro. Br J Pharmacol 1991; 102:909-915 Argentieri TM, Aiken SP, Laxminarayan S, McArdle JJ. Characteristics of synaptic transmission in reinnervating rat skeletal muscle. Pflugers Arch 1992; 421:256-261 McEvoy KM, Windebank AJ, Daube JR, Low PA. 3,4Diaminopyridine in the treatment of Lambert-Eaton myasthenic syndrome. N Engl J Med 1989; 321:15671571 Telford RJ, Hollway TE. The myasthenic syndrome: anaesthesiain a patient treated with 3.4 diaminopyridine. Br J Anaesth 1990; 64:363-366
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Bever CT Jr, Leslie J, Camenga DL, Panitch HS, Johnson KP. Preliminary trial of 3,4-diaminopyridine in patients with multiple sclerosis. Ann Neurol 1990; 27:421-427 van Diemen HA, Polman CH, van Dongen TM, van Loenen AC, Nauta H, Taphoom MJ, et al. The effect of 4aminopyridine on clinical signs in multiple sclerosis: a randomized, placebo-controlled, double-blind, cross-over study. Ann Neurol 1992; 32:123-130 van Diemen HA, Polman CH, van Dongen MM, Nauta JJ, Strijers RL, van Loenen AC, et al. 4-Aminopyridine induces functional improvement in multiple sclerosis patients: a neurophysiological study. J Neurol Sci 1993; 116:220-226 Jones RE, Heron JR, Foster DH, Sne1gar RS, Mason RJ. Effects of 4-aminopyridine in patients with multiple sclerosis. J Neurol Sci 1983; 60:353-362 Lundh H, Nilsson 0, Rosen I. Treatment of Lambert-Eaton syndrome: 3,4-diaminopyridine and pyridostigmine. Neurology 1984; 34:1324-1330 Simpson LL. A preclinical evaluation of aminopyridines as putative therapeutic agents in the treatment of botulism. Infect Immun 1986; 52:858-862 Palace J, Wiles CM, Newsom-Davis J. 3,4-Diaminopyridine in the treatment of congenital (hereditary) myasthenia. J Neurol Neurosurg Psychiatry 1991; 54:1069-1072 Dyck PJ, Chance P, Lebo R, Camey JA. Hereditary motor and sensory neuropathies. In: Dyck PJ, Thomas PK, Griffin JW, Low PA, Poduslo JF, editors. Peripheral Neuropathy. Vol 2. 3rd ed. Philadelphia: Saunders, 1993: 1094-1136 Comblath DR, Asbury AK, Albers JW, Feasby TE, Hahn AF, McLeod JG, et al. Research criteria for diagnosis of chronic inflammatory demyelinating polyneuropathy (CIDP): report from an Ad Hoc Subcommittee of the American Academy of Neurology AIDS Task Force. Neurology 1991; 41:617-618 Parry GJ. Motor neuropathy with multifocal conduction block. In: Dyck PJ, Thomas PK, Griffin JW, Low PA, Poduslo JF, editors. Peripheral Neuropathy. Vol 2. 3rd ed. Philadelphia: Saunders, 1993: 1518-1524 Dyck PJ. Detection, characterization, and staging of polyneuropathy: assessed in diabetics. Muscle Nerve 1988; 11:21-32 Dyck PJ, Kratz KM, Lehman KA, Kames JL, Melton LJ III, O'Brien PC, et al. The Rochester Diabetic Neuropathy Study: design, criteria for types of neuropathy, selection bias, and reproducibility of neuropathic tests. Neurology 1991; 41:799-807 Dyck PJ, Kames JL, Daube J, O'Brien P, Service FJ. Clinical and neuropathological criteria for the diagnosis and staging of diabetic polyneuropathy. Brain 1985; 108:861-880 Dyck PJ, Kames JL, Gillen DA, O'Brien PC, Zimmerman IR, Johnson DM. Comparison of algorithms of testing for use in automated evaluation of sensation. Neurology 1990; 40:1607-1613 Dyck PJ, Kames J, O'Brien PC, Zimmerman IR. Detection thresholds of cutaneous sensation in humans. In: Dyck PJ, Thomas PK, Griffin JW, Low PA, Poduslo JF, editors. Peripheral Neuropathy. Vol 1. 3rd ed. Philadelphia: Saunders, 1993: 706-728 Jankowska E, Lundberg A, Rudomin P, Sykova E. Effects of 4-aminopyridine on transmission in excitatory and inhibitory synapses in the spinal cord. Brain Res 1977; 136:387-392 Den Hertog A, Pielkenrood J, Biessels P, Agoston S. The effect of some new aminopyridines on mammalian non-
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myelinated nerve fibres. Eur J Pharmacol 1983; 94:353355 Al-Zamil ZM, Bagust J, Kerkut GA. The effect of diaminopyridines on the activity recorded in the dorsal roots of isolated spinal cord. Gen Pharmacol 1989; 20:747-753 Kirsch GE, Narahashi T. 3,4-Diaminopyridine: a potent new potassium channel blocker. Biophys J 1978; 22:507-512 Kirsch GE, Narahashi T. Site of action and active form of aminopyridines in squid axon membranes. J Pharmaco1Exp Ther 1983; 226:174-179 Augustine GJ. Regulation of transmitter release at the squid giant synapse by presynaptic delayed rectifier potassium current. J Physiol 1990; 431:343-364 Yawo H, Kojima H, Kuno M. Low-threshold, slow-inactivating Na ' potentials in the cockroach giant axon. J Neurophysiol 1985; 54:1087-1100 Bergin PS, Miller DH, Hirsch NP, Murray NM. Failure of 3,4-diaminopyridine to reverse conduction block in inflammatory demyelinating neuropathies. Ann Neurol 1993; 34:406-409 Lemeignan M, Millart H, Lamiable D, Molg6 J, Lechat P. Evaluation of 4-aminopyridine and 3,4-diaminopyridine penetrability into cerebrospinal fluid in anesthetized rats. Brain Res 1984; 304:166-169 Pelhate M, Pichon Y. Relative efficacy of 4-AP and 3,4-DAP on K currents in giant axons of Loligo forbesi [abstract]. J Physiol 1984; 353:79P Dyck PJ, O'Brien PC. Meaningful degrees of prevention or improvement of nerve conduction in controlled clinical trials of diabetic neuropathy. Diabetes Care 1989; 12:649-652 Russell JW, Kames JL, Dyck PJ. Sural nerve myelinated fiber density differences associated with meaningful changes in clinical and electrophysiological measurements [abstract]. Ann Neurol 1993; 34:305 Marshall IG. Structure-activity relationships amongst aminopyridines. In: Lechat P, Thes1eff S, Bowman WC, editors. Aminopyridines and Similarly Acting Drugs: Effects on Nerves, Muscles and Synapses. Oxford (England): Pergamon Press, 1982: 145-162 Katz B, Miledi R. Estimates of quantal content during 'chemical potentiation' of transmitter release. Proc R Soc Lond B BioI Sci 1979; 205:369-378 Khan RA, Lemeignan M. Effects of 3,4-diaminopyridine on mechanical and electrical responses of frog single muscle fibres. ActaPharmacol Toxicol (Copenh) 1983; 52:181-187 Stefoski D, Davis FA, Fitzsimmons WE, Luskin SS, Rush J, Parkhurst GW. 4-Aminopyridine in multiple sclerosis: prolonged administration. Neurology 1991; 41:1344-1348 Hensel H, Boman KKA. Afferent impulses in cutaneous sensory nerves in human subjects. J Neurophysiol 1960; 23:564-578 Iggo A. Temperature discrimination in the skin. Nature 1964; 204:481-483 Hensel H, Iggo A. Analysis of cutaneous warm and cold fibres in primates. Pflugers Arch 1971; 329:1-8 Goh JW, Kelly ME, Pennefather PS. Electrophysiological function of the delayed rectifier (IK) in bullfrog sympathetic ganglion neurones. Pflugers Arch 1989; 413:482-486 van Diemen HA, Polman CH, Koetsier IC, van Loenen AC, Nauta Jl, Bertelsmann FW. 4-Aminopyridine in patients with multiple sclerosis: dosage and serum level related to efficacy and safety. Clin Neuropharmaco1 1993; 16:195-204
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Treatment of Stable Chronic Demyelinating Polyneuropathy With 3,4-Diaminopyridine JAMES
w. RUSSELL, M.D.,* ANTHONY J. WINDEBANK, M.D., AND C. MICHEL HARPER, JR., M.D.
• Objective: To determine whether 3,4-diaminopyridine (3,4-DAP) would improve clinical or electrophysiologic function in patients with stable chronic demyelinating polyneuropathy. • Design: We conducted a prospective, randomized, placebo-controlled, blinded, crossover study of 3,4-DAP in 34 patients with demyelinating polyneuropathy. • Material and Methods: Of the 17 men and 17 women, who were 21 to 80 years of age, 27 had hereditary motor and sensory neuropathy type I and 7 had acquired demyelinating polyneuropathy. Treatment consisted of stepped doses of 3,4-DAP (increasing to 20 mg four times daily) or placebo for 4 days. Pretreatment and posttreatment determination of the Neurologic Disability Score (NDS); isometric muscle strength testing; median, ulnar, and peroneal nerve conduction studies; and measurement of serum 3,4DAP were performed. Quantitative computer-assisted sensory examinations were done in five patients. • Results: The results for the final day of treatment with 3,4-DAP or placebo and the differences between Improved treatment for acquired demyelinating neuropathies, such as chronic inflammatory demyelinating neuropathy and multifocal motor neuropathy with conduction block, has become available during the past decade. Currently, no effective therapy is available for hereditary demyelinating neuropathies, such as hereditary motor and sensory neuropathy (HMSN) type 1. Patients who receive immune-modulating treatment for inflammatory demyelinating neuropathies frequently have chronic disability.!? therefore, a need exists for symptomatic therapy. From the Department of Neurology, Mayo Clinic Rochester, Rochester, Minnesota. *Current address: National Institute of Neurological and Communicative Disorders and Stroke, National Institutes of Health, Bethesda, Maryland. This study was supported in part by Grant FD-R-000664 (ROl) from the Food and Drug Administration and Grant RR 00585 from the National Institutes of Health, Public Health Service. Address reprint requests to Dr. A. J. Windebank, Department of Neurology, Mayo Clinic Rochester, 200 First Street SW, Rochester, MN 55905. Mayo Clin Proc 1995; 70:532-539
pretreatment and posttreatment findings for total NDS, sensory NDS, isometric muscle strength testing, compound muscle action potential amplitude, sensory nerve action potential amplitude, motor and sensory conduction velocities, and vibration and cold detection thresholds did not vary significantly. A small improvement of 4 points in the motor NDS (P<0.05) was found. Five patients with electrophysiologic conduction block had no significant reduction in the degree of block. • Conclusion: Because no improvement was noted in most measurements of neurologic function, despite use of high doses of drug, 3,4-DAP is unlikely to be beneficial in the treatment of stable chronic demyelinating polyneuropathy. (Mayo Clin Proc 1995; 70:532-539) 4-AP = 4-aminopyridine; CIDP = chronic inflammatory demyelinating polyneuropathy; CMAP = compound muscle action potential; 3,4-DAP = 3,4-diaminopyridine; HMSN =hereditary motor and sensory neuropathy; IMT = isometric muscle strength testing; NCS =nerve conduction studies; NDS =Neurologic Disability Score; SNAP =sensory nerve action potential
In the normal myelinated axon, voltage-sensitive sodium channels are densely clustered (approximately l,OOO/J..lm2) in the axonal membrane at the node of Ranvier'v and at a lower density (approximately 25/J..lm2) in the internodal axonal membrane," whereas fast K+ channels, sensitive to 4aminopyridine (4-AP), are present under myelin in the internodal or paranodal region.v' These K+ channels are thought to assist in the generation of internodal resting potential," to prevent reexcitation, and to stabilize firing properties after the action potential." In regions of paranodal and internodal demyelination, saltatory action potential propagation is inhibited and may become physiologically blocked. As fast K+ channels become exposed, repolarization is impaired. The net effect is slowing of conduction of the action potential and delayed repolarization. In animal studies, certain aminopyridines are able to block the fast K+ channels and are able to improve conduction in regions of nerve demyelination. 10,11 Aminopyridines such as 4-AP have no effect on the action potential waveform or firing properties of mature 532
© 1995 Mayo Foundation for Medical Education and Research
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Mayo Clio Proc, June 1995, Vol 70
myelinated axons, but they do increase the duration and amplitude of the compound action potential in unmyelinated and regenerating myelinated fibers.v" When internodal demyelination occurs, exposure of fast K+ channels holds the axonal membrane close to the potassium equilibrium potential. Blockage of these channels by 4-AP improves the conduction safety factor" and may result in restoration of conduction and reduction of conduction block.":" In addition to these effects on the axonal membrane, aminopyridines enhance neurotransmission at the neuromuscular junction in both animal models'"-" and humans.v-" The observed effects in the demyelinated axon have led to therapeutic trials with aminopyridines in multiple sclerosis. Some studies have shown small improvements in neurologic function and visual evoked response latencies,":" but improvement has not been uniformly observed." Increasing the release of acetylcholine at the neuromuscular junction has been shown to be beneficial in the treatment of LambertEaton myasthenic syndrome,"> type A botulism," and certain variants of congenital myasthenia." Although studies in animal models of demyelinating neuropathy seem promising, no controlled trial of 3,4diaminopyridine (3,4-DAP) in human neuropathy has been previously conducted. In the current study, subjects who had stable demyelinating neuropathy were entered in a doubleblind, placebo-controlled, crossover trial and treated with 3,4-DAP to determine whether clinical or electrophysiologic function would improve. METHODS
Selection ofPatients.-Patients 20 to 80 years of age were eligible for inclusion in the study. All patients underwent a complete clinical examination, electrophysiologic study, supportive blood tests, and, when necessary, cerebrospinal fluid examination and nerve biopsy at Mayo Clinic Rochester to determine eligibility. In order to avoid improvement or decline in function due to the natural history of the disease, only patients with a stable demyelinating neuropathy, defined as a stable clinical condition for at least 6 months before entry in the study, were eligible to participate. Eligible patients had one of three clinical diagnoses: HMSN type I, chronic inflammatory demyelinating polyneuropathy (ClDP), or multifocal motor neuropathy and conduction block. Patients were excluded from analysis if their neuropathy could have been partially or wholly due to a disorder other than these three clinical conditions or if any other medical condition existed that might have affected the neuropathy or evaluation during the trial. Patients with a predisposition to seizures or to cardiac, hepatic, or renal disease were excluded from the study. The diagnosis of HMSN type I was based on the clinical and genetic history, examination, electrophysiologic studies, and, when appro-
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priate, sural nerve pathologic findings and genetic tests, with application of criteria previously described by Dyck and associates." Patients diagnosed with chronic inflammatory demyelinating neuropathy fulfilled the research criteria of the American Academy of Neurology AIDS Task Force." Subjects were diagnosed as having multifocal motor neuropathy and conduction block if they had an asymmetric motor neuropathy, electrophysiologic conduction block (see subsequent material), and other supportive clinical and laboratory findings, including increased levels of antibodies to GMl,3° Patients treated with immunosuppressive agents had no change in dosage for at least 6 months before entry into the study. Study Design.-3,4-DAP was obtained in powder form from Regis Chemical Company (Morton Grove, Illinois). The powder was formulated with lactose into 5-mg capsules. Placebo capsules were formulated from lactose. Four serum samples were obtained from each patient-before the trial was begun, after the washout period, and after a 20-mg dose of placebo or 3,4-DAP had been taken on the final day of each phase of the crossover trial. Serum levels of 3,4-DAP reach a peak after 60 minutes and then decay during a period of 1 to 200 minutes; thus, the medication could be administered four times a day. Blood specimens were obtained in the morning I hour after the administration of 3,4-DAP or placebo. Protocol.-The study protocol was approved by the Mayo Clinic Institutional Review Board, and written informed consent was obtained from each participant. Patients were admitted to the General Clinical Research Center during treatment. The study was designed as a double-blind, crossover trial. Subjects who enrolled in the study were treated with either 3,4-DAP (active treatment) or placebo during an initial phase that lasted 4 days, followed by a washout period of at least 5 days, during which they received neither placebo nor 3,4-DAP. After the washout period, subjects entered the crossover phase, during which they received 4 days of treatment with whichever medication (3,4-DAP or placebo) had not been administered initially. For randomization to 3,4-DAP or placebo during the initial phase, a random number system generated by the Mayo Clinic Pharmacy was used. Medication was coded by the pharmacy, and only the study pharmacist was aware of the code. Nursing staff ensured that all medication was taken by the subjects, and empty containers were cross-checked by the pharmacy. The initial dosage was 5 mg of 3,4-DAP or placebo, four times a day for the first day; the dosage was doubled on the second and third days and then kept at 20 mg four times a day for the fourth day. A Neurologic Disability Score (NOS) was determined before the initial and crossover phases were begun, after treatment, and daily while medication was administered. Isometric muscle strength testing,
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3,4-DIAMINOPYRIDINE IN DEMYELINATING NEUROPATHY
electrophysiologic studies, and sensory testing were performed before subjects entered the study and on the fourth (last) day of each phase of the trial; the tests were done at similar times of the day and with use of identical techniques. These tests were performed within I to 2 hours after the subjects took the test drug, for reflection of an optimal medication effect. Venipuncture for serum electrolytes, complete blood cell count, and 3,4-DAP level was performed before each phase of the crossover trial and on the fourth (last) day of each phase. Each patient completed a daily medication adverse effect report, with the assistance of the nursing staff. In order to avoid unblinding the examining physician, patients were asked to report any major adverse medication effects to a physician who was not participating in the study. NDS and Biomechanical Evaluation.-Results of a neurologic examination were graded by using a previously established scoring system (the NDS);31,32 this assessment was performed by a single blinded examiner to avoid interexaminer variability. With use of this system, strength was graded against normal expectations for the patient's age and sex. The range of scores was as follows: 0 = normal strength; I = mild weakness (25% weaker than normal); 2 = moderate weakness (50%); 3 = severe weakness (75%); and 4 = unable to generate any force (100%). When necessary, subclassifications of weakness (for example, 3.25, 3.5, and 3.75) were allowed. Muscle stretch reflexes were graded as follows: normal =0; decreased = 1; and absent = 2. Sensation (touch-pressure, pinprick, vibration, and joint position sense) was assessed on the dorsum of the index finger and great toe (near the base of the nail) and was graded as follows: normal = 0; decreased = 1; and absent = 2. This system has been shown to be reproducible and to have low intraobserver variability, particularly for total NDS and weakness NDS.32 Worsening neurologic function is indicated by an increase in the NDS. The total NDS was further subdivided into a motor NDS (strength evaluation only) and a sensory NDS (sensory determinations only). Findings were compared between 3,4-DAP and placebo phases by using mean summated NDS (total, motor, and sensory) and mean delta NDS (difference between NDS before and after treatment). Biomechanical Isometric Strength Evaluation.-Biomechanical isometric muscle strength testing (IMT) was done bilaterally for the following functions: elbow flexion, wrist flexion, thumb abduction, index finger abduction, key pinch, knee extension, and ankle extension. All studies were performed by one of two physical therapists. The maximal isometric force (best of three trials) was measured for each determination. Measurements (in kilograms per centimeter) were made bilaterally, corrected when necessary for dominance, and expressed as percent of normal. Data were com-
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pared by using mean summated biomechanics scores (for all muscles tested, the proximal muscles, and the distal muscles) and delta scores (difference between scores after medication and at baseline). Electrophysiologic and Sensory Threshold Studies.Standard techniques" were used for nerve conduction studies (NCS), and care was exercised to use identical placement of electrodes and to maintain limb temperature at or above 32°C by using surface thermistors and infrared lamps. When necessary, the limbs were immersed in warm water for 15 minutes at 38°C. Distal median, ulnar, and peroneal compound muscle action potential (CMAP), median and ulnar sensory nerve action potential (SNAP), and motor and sensory conduction velocities were determined, Comparisons between placebo and active phase NCS were made by using mean summated CMAPs (sum of median and ulnar CMAPs), summated SNAPs (sum of median and ulnar SNAPs), summated motor conduction velocities (sum of median and ulnar motor velocities), summated sensory conduction velocities (sum of median and ulnar sensory velocities), delta NCS (difference between NCS value after 3,4-DAP phase [or placebo phase] and baseline value), and individual nerve measurements. The use and validity of summated nerve and muscle action potential and conduction velocity data for detection of change have been extensively discussed.P-" For determining the presence of conduction block, the following requirements were met: a supramaximal stimulus was used and the amplitude and the negative peak CMAP area were reduced 50% or more with proximal stimulation, in the absence of dispersion, along long nerve segments normally unaffected by compression palsies. Cold and vibration detection thresholds were measured on the dorsum of the foot and toe, respectively, with use of the computer-assisted sensory examination IV device." Results were obtained by using a forced-choice method'<" and expressed as deviations from normal for age, site, and sex. Sensory detection thresholds, while subjects were in the active and placebo phases, were compared by using mean summated normal deviates for cold or vibration and mean delta normal deviates (difference between baseline and postmedication results). Statistical Analysis.-Quantitative measures of function with 3,4-DAP or placebo were compared by using Student's t test for paired values or the nonparametric Wilcoxon signed rank test for data that were not normally distributed. The Pearson correlation coefficient was used to determine the association between the serum level of 3,4-DAP and measures of neurologic function. Statistical significance was defined as a P value of less than 0.05. For ease of comparison of data, results were expressed as mean ± standard error of the mean.
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3,4-DIAMINOPYRIDINE IN DEMYELINATING NEUROPATHY
Mayo Clin Proc, Ju ne 1995, Vol 70
RESULTS Thirty-four patients with stable chronic demyelinating polyneuropathy entered the protocol, and all patients completed the initial and crossover phases of the study. The 34 patients (17 men and 17 women) ranged in age from 21 to 80 year s (mean, 48); 2 patients were Hispanic and 1 was AfroAmerican. Of the 34 patients, 27 had stable HMSN type I, 5 had multifocal motor neuropathy and conduction block, and 2 had CIDP with no electrophysiologic conduction block. Neurologic Disability Score.-In the 34 study patients, the NDS was determined before and after each arm of the crossover triaL No significant difference was noted in the mean total NDS at the start of the placebo phase (72.3 ± 5.7) and at the start of the active phase (73.2 ± 5.6) or between the total NDS at the start (72.3 ± 5.7) and the end (68.2 ± 5.8) of the placebo phase. The mean delta total NDS (difference between total NDS at start and end of each phase) for the 3,4DAP arm of the trial was not significantly different from that for the placebo phase (Table 1). Only four patients had a mild increase in total NDS ; the total NDS in the rest remained unchanged or showed a mild decrease. The motor component of the NDS increased from baseline while patients were receiving 3,4-DAP. In comparison with placebo, a 4-point improvement was detected in the mean delta motor NDS while subjects were taking the drug (P<0.05); however, the difference between the mean motor NDS for active (40.87 ± 4.26) and placebo (44.33 ± 5.43) groups at the end
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of each treatment arm did not reach significance (P = 0.051 ). No difference was observed in the mean delta sensory NDS , or other measures of sensory NDS, between subje cts during the active phase and the placebo phase of the stud y. In patients with multifocal motor neuropathy or CIDP, no statistical difference was noted in mean delta total NDS, motor NDS , or sensory NDS after the 3,4- DAP triaL
Biomechanical Isometric Strength Evaluation.-Mean values from biomechanical IMT were determined in 34 patients. Altho ugh the mean IMT score increased slightly after the active phase (51.04 ± 3.97) in comparison with the placebo phase of the study (50.20 ± 4.29) , the difference did not reach significance. Delta IMT results for active (5.60 ± 1.65) and placebo (4.60 ± 0.94) phases of the trial were not significantly different. When IMT scores for proximal and distal muscles were con sidered separately, no significant difference in results was noted after 3,4-DAP or placebo phases. In patients with multifocal motor neuropathy or CIDP, no significant difference was found in mean delta IMT results after treatment with 3,4-DAP. Electrophysiologic Studies.-Median and ulnar nerve conduction studies were performed in 34 subjects and peroneal studies in 22. Summated CMAP amplitudes (sum of ulnar and median CMAP amplitudes) were determined in 32 patients; both CMAP amplitudes were unrecordable in 2 patients. Summated SNAP amplitudes could be recorded in only 13 patients. The mean delta summated CMAP ampli-
Table 1.-8umma ry of Neurologic Endpoints in Study Subjects With Stable Chronic Demyelinating Polyneuro pathy* Determination
No.t
~Active*
~Placebo§
Significance
TotalNOSf Motor NOS SensoryNOS Biomechanics LCMAP(mV) LSNAP(J1V) Peroneal CMAP (mV) LMCV (rn/s) LSCV (m/s) Vibration Cold detection
34 34 34 34 32 13 8 31 10 5 5
7.20± 1.59 5.61 ± 1.49 1.56± 0.38 5.60 ± 1.65 0.22 ± 0.19 1.57± 2.30 0.02 ±0.15 0.74 ± 0.75 14.10± 9.04 0.06 ±0.08 0.23 ±0.20
4.39 ± 1.21 0.81 ± 1.84 1.12±0.40 4.60±0.94 0.17 ± 0.38 1.35± 1.58 0.31 ±0.15 1.01 ± 1.03 7.20±7.23 0.1O±0.06 0.01 ± 0.10
NS P<0.05 NS NS NS NS NS NS NS NS NS
*Results are recorded as mean ± standard error of the mean. LCMAP = summated compoundmuscle action potentialamplitude for median and ulnar nerves; LMCV = summated motor conduction velocity for ulnar and median nerves; NOS = Neurologic Disability Score; NS = not statistically significant; LSCV = summated sensory conductionvelocityfor ulnar and mediannerves; LSNAP = summatedsensory nerve action potential amplitude for ulnar and median nerves. [Number of patients in whom a result could be obtained. *Result on final day of 3,4-diaminopyridine phase of crossoverstudy- result immediately before drug trial was initiated. §Resulton final day of placebo phase of crossover study - result immediately before placebo phase was begun. #Total NOS = combineddata from the motor NOS, sensory NOS, and reflex NOS.
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3,4-DIAMINOPYRIDINE IN DEMYELINATING NEUROPATHY
tude and mean delta summated SNAP amplitude were similar in subjects during the 3,4-DAP and the placebo phases of the study (Table I). The mean summated CMAP amplitude (6.24 ± 0.87 mV) and mean summated SNAP amplitude (27.28 ± 9.99 flV) after treatment with 3,4-DAP were not significantly different from the summated CMAP amplitude (6.30 ± 0.91 mY) and summated SNAP amplitude (27.42 ± 11.76 flV) after placebo. Mean CMAP amplitude for the ulnar and median nerves, separately, remained unchanged after treatment with 3,4-DAP. Peroneal CMAP amplitudes could be recorded in only eight subjects. The mean delta summated CMAP amplitude for each phase of the trial and the mean summated CMAP amplitude after 3,4-DAP treatment (0.57 ± 0.19 mY) did not vary significantly from the result after the placebo phase (0.71 ± 0.23 mY). Ulnar and median forearm segment motor conduction velocities could be recorded in 31 patients and sensory conduction velocities in 10. Mean delta summated motor and sensory conduction velocities did not vary significantly after 3,4-DAP treatment (Table I). After treatment with 3,4-DAP, the mean summated motor conduction velocity (49.94 ± 4.07 m/s) and the mean summated sensory conduction velocity (95.0 ± 10.47 m/s) did not vary significantly from the mean summated motor conduction velocity (50.23 ± 3.92 m/s) and the mean summated sensory conduction velocity (88.7 ± 14.42 m/s) after placebo. Considered separately, mean median and ulnar forearm motor and sensory conduction velocities were not significantly altered after 3,4-DAP treatment. Peroneal conduction velocities were unrecordable in most patients. Patients with multifocal motor neuropathy and conduction block or those with CIDP, when considered separately from the group with HMSN type I, showed no significant improvement in any electrophysiologic variable. In patients with multifocal motor neuropathy, partial or complete electrophysiologic conduction block was present in a total of six ulnar or median nerves. The mean percentage reduction in negative peak CMAP area (percentage conduction block) at baseline was 68.5 ± 7.3% for these nerves. The mean percentage conduction block was 72.3 ± 6.6% after treatment with 3,4-DAP and 69.8 ± 8.0% after administration of placebo. No significant improvement was found in the mean percentage conduction block for all affected nerves or in individual nerves after administration of 3,4-DAP. Sensory Detection Thresholds.- Vibration and cold detection thresholds were measured on the dorsal aspect of the foot in five patients, and results were expressed as normal deviates (Table I). The mean delta cold and vibration detection thresholds did not differ significantly when subjects were taking 3,4-DAP or placebo, although slight decreases were noted during the active medication phase. After 3,4DAP treatment, the mean normal deviate for cold detection
Mayo Clin Proc, June 1995, Vol 70
was 1.77 ± 0.4 and for vibration detection was 2.11 ± 1.2, in comparison with 2.02 ± 0.18 for cold detection and 2.14 ± 0.1 for vibration detection after placebo. Medication Levels and Side Effects.-Serum samples were obtained in 33 patients. No significant change in serum electrolytes or complete blood cell count was observed during the trial in any patient. As expected, the 3,4-DAP level was unrecordable in all subjects before entrance into the trial, after the washout period, and after the placebo phase. The mean level I hour after taking 20 mg of 3,4-DAP was 54.86 ± 5.85 ng/mL. Although mean 3,4-DAP levels were higher in women (58.82 ± 8.93 ng/mL) than in men (47.67 ± 4.76 ng/mL), they were not statistically significantly different. No association was found between the serum level of 3,4-DAP and mean delta total NDS, mean delta motor NDS, mean delta sensory NDS, mean delta summated CMAP amplitude, mean delta summated SNAP amplitude, mean delta summated motor conduction velocity, or mean delta summated sensory conduction velocity. For a 4-day treatment period, adverse effects were mild, and all patients were able to tolerate the full dose of 3,4-DAP. One patient, in whom light-headedness developed, requested a reduced dose of medication. The subject was found to be taking placebo at the end of the study and had not had postural symptoms during the 3,4-DAP phase of the trial. Four subjects (12%) had no adverse symptoms during 3,4-DAP treatment. The most common symptom related to use of medication was facial (predominantly perioral) paresthesia (Table 2). This symptom was most likely to occur when the subject was taking 80 mg/day. Most side effects developed within 1 hour after the medication was taken and were transient. Generalized muscle fatigue was infrequent but more persistent. Although fluctuations occurred in determinations of motor and sensory function, 3,4DAP did not cause significant deterioration in any of these measurements. Most adverse symptoms subsided as the subjects continued to take the medication. No patients had seizures or syncope; however, mild postural lightheadedness developed in 35% of subjects taking 3,4-DAP. Less frequently recorded adverse effects were insomnia (15%), transient urinary frequency (12%), increased tearing or nasal discharge (6%), increased sweating (6%), transient facial flushing (6%), transient hand tremor or muscle twitching (6%), headache (6%), and transient parageusia (3%). DISCUSSION The aminopyridines have been shown to affect potassium channels and the generated action potential in both myelinated and nonmyelinated axons.ll.36-38 Aminopyridine-sensitive potassium channels seem to be similar in their pharmacologic properties in many species, ranging from the squid axon":" and cockroach giant axon? to mammalian
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MayoClin Proc, June 1995,Vol70
3,4-DIAMINOPYRIDINE IN DEMYELINATING NEUROPATHY
537
Table 2.-Frequency and Duration of Side Effects During a Controlled Trial With 3,4-Diaminopyridine in 34 Patients With Stable Chronic Demyelinating Polyneuropathy Patients
Time (min) to onset of symptom
Duration
Adverse effect
No.
%
Mean
Range
Mean
Range
Facial paresthesia Postural light-headedness Paresthesia of hands or feet Muscle fatigue Nausea, abdominal discomfort, vomiting
24 12
71 35
50 48
10-120 20-60
45 min 4h
10-90 min 10 min-24h
11
10
32 29
60 50
20-120 30-75
40 min 18 h
15-90 min 1-24 h
6
18
55
15-75
9h
fibers. 1O,14,ls Although 4-AP has been shown to improve nerve conduction in demyelinated or regenerating axons in animal studies,9,10,14-16 in one human study no significant change in conduction block or clinical improvement was observed in six patients with inflammatory demyelinating neuropathies treated with 3,4-DAP. 43 Penetration of 3,4DAP into the cerebrospinal fluid is significantly less than for 4-AP. In animal studies, intracisternal injection of both drugs results in an equal frequency of occurrence of seizures; therefore, the poor penetration probably accounts for the fewer observed seizures with 3,4-DAP.44 The potassium channel blocking capacity of 3,4-DAP in comparison with 4AP varies in different animals but is greater in the squid giant axon (Loligo pea/ei) and the cockroach axon. 39,4S For these reasons, subjects were treated with 3,4-DAP rather than 4AP in this study. In the current study, 27 patients had a hereditary neuropathy with demyelinating features (HMSN type I), 2 had stable CIDP, and 5 had stable multifocal motor neuropathy and conduction block. Despite clear evidence of demyelination, no overall improvement was observed on the clinical examination, IMT, or motor conduction studies. Although the motor component of the NDS score slightly improved during administration of 3,4-DAP, this finding was not supported by the IMT. A decrease of 4 points in the motor NDS would correspond to a 25% increase of muscle strength in two muscle groups bilaterally. A change of 2 points is the minimal detectable alteration in neurologic functionr'v" however, a change of 4 points is a very minor clinical adjustment. In animal studies, 3,4-DAP has been shown to increase the quantal release of acetylcholine at the neuromuscular junction'v" after potentiation of calcium influx through voltage-gated calcium channels," and it may act directly on muscle fibers to increase twitch amplitude." Although this mechanism may explain the improvement in the motor NDS, an increase in CMAP amplitude is observed when disorders of neuromuscular transmission are treated with 3,4_DAP.19,27 We found no statistically significant in-
30 min-24h
crease in any measure of CMAP amplitude during the 3,4DAP phase in comparison with placebo. Our previous pharmacokinetic studies of treatment with 3,4-DAP in subjects with Lambert-Eaton myasthenic syndrome indicated that the peak serum concentration of drug would occur approximately 1 hour after oral administration, and results of clinical, electrophysiologic, and IMT were most improved I to 3 hours after the drug was administered (unpublished data). The electrophysiologic studies were performed on the last day of treatment, concurrent with the expected peak serum concentration of 3,4-DAP. Most likely, any positive effect by 3,4-DAP on the electrophysiologic studies would be noted at this time. The dosage of 3,4-DAP used (up to 80 mg/day) should have been adequate to elicit a response because most patients with neuromuscular transmission defects demonstrate improvement with this dose,'? and studies in patients with multiple sclerosis have shown that those who respond to 4-AP do so at doses of less than 55 mg/day.22,23,sl Furthermore, in our study, even though absorption of 3,4DAP may have been variable after oral dosing, no correlation existed between 3,4-DAP serum levels and clinical and electrophysiologic measures. In the five subjects with conduction block, no significant change in the electrophysiologic findings was observed, and either no or minimal clinical improvement was noted. This outcome was similar to the findings in six patients who had electrophysiologic evidence of conduction block-four with Guillain-Barre syndrome and two with CIDP.43 No statistically significant improvement was found in determinants of sensory function, including clinical assessment, sensory conduction studies, or measures of thermal and vibratory thresholds, with use of computer-assisted sensory examinations. This result suggests that 3,4-DAP had little effect on sensory myelinated fibers. Cold sensation activates predominantly thinly myelinated and, less frequently, unmyelinated fibers in primates and humans.v" In this study, however, afferent unmyelinated axons, such as those from polymodal nociceptors, or autonomic fibers,
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538
3,4-DIAMINOPYRIDINE IN DEMYELINATING NEUROPATHY
which may be responsive to 3,4_DAP,19,40,55 were not specifically tested. The most frequently observed adverse effect of 3,4-DAP was a mild facial (predominantly perioral) tingling sensation, which was noted by 71 % of our patients. Most adverse effects developed within 1 hour after administration of 3,4DAP and generally dissipated within 24 hours, while the same or a higher dose of the medication was maintained. Despite the range of symptoms, all patients completed the study without a reduction in the final dose of 3,4-DAP. No clinical seizures developed in any patient. The serum levels of 3,4-DAP varied considerably, a finding previously observed with 4-AP as well." The lack of correlation between the serum 3,4-DAP level and any measure of neurologic improvement suggests that the variability in serum level did not adversely affect the results of the study. Why a discrepancy would exist in the results of aminopyridine treatment between demyelinated and regenerating mammalian fibers and this human study of demyelinating neuropathy is unclear. In the animal studies, however, demyelinating lesions were usually studied in acute or subacute conditions;9,lO,14,15 perhaps the distribution and sensitivity of fast conducting potassium channels differ in the chronic demyelinating neuropathy we studied. This explanation would not clarify the lack of efficacy in subjects with Guillain-Barre syndrome described by Bergin and colleagues," although no pharmacokinetic data were available in that study and whether the serum levels were adequate is unknown. When long-term follow-up studies have been performed in animal nerves after crush injury, sensitivity to aminopyridines has progressively declined." This result may have been due to secondary axonal changes. In animal studies with aminopyridines, extremely sensitive isolated nerve preparations have usually been used to record action potentials, but the correlation of these electrophysiologic changes with improvement in function has not been specifically examined. Another possibility is that the molecular characteristics of fast potassium channels in human peripheral nerves vary from those in other mammals and may be less sensitive to aminopyridines. Whatever the reason for the difference, this study indicates that 3,4-DAP produces no clinically significant improvement in neurologic function in subjects with chronic stable demyelinating polyneuropathy.
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