- Email: [email protected]
Preserved cutaneous silent period with absent sensory nerve action potentials in peripheral nerve lesiosns
Society proceedings/
Electroencephalography and clinical Neurophysiology 98 (1996) 8P-4OP
Objective: To assess extent and type of injury and natural history in birth-related brachial plexus injury in the neonatal period using electrodiagnostic studies. Methods: Nerve conduction! studies and electromyographic examination were performed at the age of 2 weeks on neonates with clinical diagnosis of Erb’s palsy soon after birth. Follow-up studies were performed on infants who did show sustained clinical improvement. Results: Between October 1993 and January 1995, 13 neonates were diagnosed with Erb’s palsy. Ten neonates had evidence of axonal injury to the upper trunk and 5 had additional injury to the middle trunk as well. Three neonates had neurapraxia and full recovery occurred in 2 weeks. Repeat studies were performed on 3 cases and reinnervation was seen in all previously denervated muscles including those with no voluntary units on initial studies. In 5 cases, repeat examination was not performed as significant recovery had occurred. Conclusion: This study shows that the injury in neonatal Erb’s palsy involves the middle trunk frequently in addition to the upper hunk. Despite evidence of Severe axonal injury on the initial study, significant improvement occurred in all wilh conservative management. 5. Medial antebrachial nerve studies in true neurogenic thoracic outlet syndrome. - J.R. Beattie and M.A. Ross (University of Iowa Hospitals, Iowa City, IA) True neurogenic thoracic outlet syndrome (TOS) is a rare disorder in which electrodiagnostic studies (EDXS) localize the lesion to the lower trunk of the brachial plexus. Medial antebrachial (MA) nerve conduction studies in true neurogenic TOS have not been frequently reported. A 46-year-old man experienced intrinsic hand and left thenar muscle atrophy, and sensory loss involving the left fourth and fifth fingers, and the medial hand and forearm. EDX:S revealed normal amplitude left ulnar compound muscle action potential (CMAP) and median sensory nerve action potential (SNAP), absent left ulnar SNAP, and low amplitude median CMAP. The left MA SNAP was absent, but normal on the right. Needle examination revealed fibrillation potentials in the left abductor pollicis brevis and first dorsal interosseous. The left biceps, triceps and cervical paraspinal muscles were normal. A cervical spine film revealed bilateral cervical ribs, with left more prominent. This patient’s EDXS are typical of true neurogenic TOS. The absent MA SNAP confirms localization of the true neurogenic TOS lesion to the lower trunk of the brachial plexus,.as the MA nerve arises distal to the lower trunk, from the medial cord of the brachial plexus. Additional studies of the MA nerve in other cases of true neurogenic TOS will be useful to determine if this is a consistent finding. 6. Tom Dooley’s syndrome: head hanging from idiopathic cervical plexitis. - P. Wright, W.L. Bell, J. Koufman and F.O. Walker (Bowman Gray School of Medicine, Winston-Salem, NC) Subacute weakness of neck extensors commonly signifies myasthenia gravis, inflammatov myopathy, or botulism. We describe an unusual case of head hanging that resembles idiopathic brachial plexitis. A 46-year-old man developed dyspnea and transient bilateral shoulder pain. Orthopnea, hoarseness and neck extensor weakness followed, causing him to seek medical advice. Examination revealed profound, but painless weakness of neck extension, orthopnea, and paradoxical ventilation. Needle examination revealed marked fibrillation potentials and decreased recruitment of long duration, low amplitude motor units in diaphragm, laryngeal muscles, stemothyroid, splenius capitis, and bilateral C2-5 cervical pamspinal muscles. Diagnostic work-up, including imaging studies, was unremarkable with the exception of fluoroscopically proven bilateral diaphragmatic pamlysis and vocal cord paralysis by fiber optic exam. Escaping the fate of Tom Dooley, who was “bound to die,” the patient gradually regained the ability to hold his head upright and his forced vital capacity increased from 2.1 to 3.3 liters. We believe that Tom
9P
Dooley’s syndrome, head hanging, hoarseness, shoulder pain, and orthopnea, defines a syndrome of idiopathic cervical plexitis. We speculate that it bridges a spectrum of related idiopathic syndromes which include phrenic nerve paralysis, laryngeal paralysis, and brachial plexitis. 7. Central H-reflex latency from Sl root stimulation. I. Intraspinal conduction time of Sl root. - P.Y. Zhu, A. Starr, S. Haldeman and L. Cui (University of California, Irvine, CA) Introduction: We have previously reported that magnetic and percutaneous electrical stimulation of the nerve root elicited soleus H-reflex. This study reports the characteristics of central H-reflex latency (CHL) in a normal population. Objectives: To determine: (I) normal values of CHL; (2) the length of the Sl root; (3) effect on CHL of ischemia of the sciatic nerve; and (4) the clinical usefulness of CHL. Methods and results: (I) We tested 30 men and 30 women (aged 19-62 years). The Sl root was stimulated at the Sl foramen by high voltage electrical stimulation (60 cases) and magnetic stimulation (30 cases). Muscle responses were recorded from soleus with surface electrodes. CHL was defined as the difference between the peak latencies of the H- and M-waves. The mean of the CHL was 6.8 f 0.41 msec with side-to-side difference of 0.16 f 1.8 msec. There was no significant difference between CHL obtained by two methods of stimulation. (2) In 15 cadavers, the mean length of the Sl dorsal root was 17.5 * 0.3 cm, with an la CV of approximately 67.3 m/set. (3) In 2 normal subjects, ischemia of the sciatic nerve produced by a cuff around the thigh abolished the PTN evoked H-reflex, while the CHL was not altered. (4) In 4 patients with Guillain-BamZ syndrome, disk hemiation, disk hemiation and polyneuropathy, and lumbosacral plexopathy, respectively, CHL showed specific characteristics confirming the diagnosis in each patient. Conclusions: Central H-reflex latency reliably represents the intraspinal conduction time of the Sl root, which is of significant clinical usefulness. 8. Cutaneous silent period abnormalities in the carpal tunnel syndrome. - S.K. Aurora, B.K. Ahmad and T.K. Aurora (Henry Ford Hospital and Health Sciences Center, Detroit, MI) Background: Physiological mechanisms underlying the electromyographic silent period (SP) are unclear. There have been no previous studies on SP in carpal tunnel syndrome (CTS). Methods: Cutaneous SP on stimulating digits 2 and 5 was obtained in 20 healthy volunteers, aged 24-45 (mean 32). and in 19 patients with clinical CTS, aged 25-73 (mean 42). SP onset, duration and end were measured in each of 10 trials and averaged. Patients were classified as having mild, moderate or severe CTS based on nerve conduction studies. Paired r tests were used for statistical analysis. Results: In the 2 patients with severe CTS, digit 2 SP was unobtainable. In control subjects, digit 2 SP mean duration was 36.9 msec (S.D. 10.2). In patients, SP mean duration was 51.8 msec (S.D. 16.6) (P= 0.001). In control subjects, the mean SP end was 113.4 (S.D. 10.05) and in patients the mean SP end was 127.3 msec (S.D. 16.2) (P = 0.005). There were no significant differences in digit 2 SP onset and all measures of digit 5 SP. Conclusion: (1) Cutaneous SP is abnormal in CTS, being absent in severe and prolonged in mild to moderate cases. (2) Cutaneous SP research patients should be screened for CT.% S.K. Aurora, M.D., Junior Member Recognition Award. 9. Preserved cutaneous silent period with absent sensory nerve action potentials in peripheral nerve lesions. - V.M. Scruggs and J.J. Wertsch (Medical College of Wisconsin, Milwaukee, WI) Introduction: In peripheral nerve lesions with absent sensory nerve action potentials (SNAPS), an ability to demonstrate axon continuity would be helpful in surgical planning.
1OP
Society proceedings / Electroencephulography and clinical Neurophysiology 98 (1996) 8P4OP
Objective: The purpose of this study was to explore if the cutaneous silent period (CSP) could be obtained in patients with peripheral nerve lesions who have clinical sensory loss and absent SNAPS. Methods: Three patients with isolated ulnar mononeuropathies were studied. All had absent digital ulnar sensory responses; two had marked motor involvement. The CSP response was elicited by applying electrical stimuli to the little finger with surface EMG recorded from the ipsilateral thenar eminence during mild voluntary contraction. Results: The CSP was present in all 3 patients. The duration of the silent period averaged 58 msec with an average onset of 97 msec in the 2 patients measured. With increasing stimulus intensity, the duration of the silent period increased. In 1 individual, comparison with the contralateral side revealed no major differences. Conclusions: The preservation of the CSP in peripheral nerve lesions with absent SNAPS is of interest for further study of the underlying physiologic mechanisms and its clinical applicability in potential surgical cases. V.M. Scruggs, Junior Member Recognition Award.
10. Factors affecting mixed nerve and cutaneous silent periods. J.M. Shefner and E.L. Logigian (Brigham and Women’s Hospital, Boston, MA)
Introduction: Silent periods (SPs) have been studied with increasing frequency to evaluate central movement disorders. However, it is clear that properties of SPs vary with the experimental conditions. Objectives: We wished to evaluate the duration and latency of mixed nerve and cutaneous SP as stimulus intensity and strength of voluntary contraction were systematically altered. Methods: In 10 normal subjects, SPs were obtained from the first dorsal interosseous muscle with stimulation of digit 5 or the ulnar nerve at the wrist. Strength of voluntary contraction was varied and measured with a strain gauge; stimulus intensity was varied from threshold to 12 x threshold. Results: For both mixed nerve and cutaneous SPs, the latency for resumption of voluntary activity increased with increasing stimulus intensity or with decreased voluntary contraction. For the cutaneous SP, the initial SP latency decreased with increasing stimulus intensity or decreased contraction force. Facilitation and inhibition as measured by force changes also varied with stimulus strength and contraction force. Conclusions: The parameters most frequently measured for the cutaneous and mixed nerve SPs vary systematically with experimental conditions. Careful control of these factors is necessary if SPs are to be used as tools for diagnosis or pathophysiological study.
11. Reversal of neuromuscular blockade in coral snake bites: determination by repetitive nerve stimulation and quantitative EMG. - J.E. Gutierrez and L.F. Villota (Universidad de1 Valle, Cali, Colombia)
a-Bungarotoxin, secreted by coral snakes, binds to the postsynaptic acetylcholine receptor and causes a non-depolarizing neuromuscular blockade. We present the neurophysiological studies of a 26-year-old man admitted to the ICU 8 h after being bitten by a Micrurus mipartita mipartita. Initial examination revealed normal sensation, flaccid quadriplegia, areflexia, diplopia, bilateral ptosis and respiratory arrest requiring mechanical ventilation. On admission, motor and sensory latencies were normal with a 50-60% decrease on compound muscle action potential amplitudes. No F-waves could be recorded. Repetitive stimulation (5 Hz) showed a 29% decrement in amplitude and a 34% decrement in area (5: 1 atea ratio = 66%). Motor unit action potentials (MUAPS) were increased in duration (19.2 f 2.5 msec), phases (5 f 2.1). turns (6 f 1.51,variability (“jiggle”) and decreased in amplitude (I59 f 25 /.~Vuv) and area (235 f 52 pV/ms).
Reversal of the neuromuscular blockade was evident 2 hours after specific hyperimmune serum application. Repetitive nerve stimulation showed a 14% decrement in amplitude and an 11% decrement in area (5: 1 area ratio = 89%). MUAP parameters were as follows: Duration (9.8 f 3.85 msec), phases (2 f 1.3), turns (2 f 1.5), amplitude (590 f I I5 PV), area (1116 f 352 pV/msec). The muscle strength increased dramatically. Based on the results, only one-third of the usual antivenin dosage was given. The patient recovered completely within 8 days. Electrophysiological testing detects the reversal of neuromuscular blockade produced by a-bungarotoxin and helps to determine the appropriate antivenin dosage, diminishing the risk of anaphylactic reactions. 12. The electrophysiologic basis of the ice pack test in myasthenia gravis. - J.A. Brooks, S.J. Oh, G.C. Claussen and T.J. Moskowitz (University of Alabama at Birmingham, Birmingham, AL) Introduction: The ice pack test is a simple aid in the diagnosis of myasthenia gravis. However, the original descriptions of this test did not include electrodiagnostic studies to document electrophysiologic improvement. Objective: To study the effect of the ice pack test on the decremental response in myasthenia gravis. Methods: Two patients with generalized myasthenia gravis and bilateral ptosis, who had positive ice pack tests, underwent repetitive nerve stimulation of one facial nerve. This procedure was performed at room temperature, with eyelid skin temperature between 34’C and 34.5”C. and after applying an ice pack to one eye. Results: The decremental response at 2 Hz stimulation at room temperature was 9.3% in patient 1 and 80% in patient 2, improving to 5.7% and 37%. respectively, after application of the ice pack. Improvement of ptosis also occurred in both patients. Conclusion: The ice pack test produces electrophysiologic as well as clinical improvement in myasthenia gmvis. J.A. Brooks, Junior Member Recognition Award. 13. Frequency and distribution of EMG fmdings in Lambert-Eaton myasthenic syndrome. - R.W. Tii, D.B. Sanders and J.M. Massey (Duke University Medical Center, Durham, NC) Objectives: To determine the distribution of abnormality, and to see which test was most likely to demonstrate abnormality in the Lambert-Eaton myasthenic syndrome (LEMS). Methods: In 26 clinically diagnosed LEMS patients, compound motor action potential (CMAP) amplitude, decrement to 3 Hz repetitive nerve stimulation (RNS), and potentiation of CMAP amplitude after maximum voluntary contraction (MVC) were measured in the abductor digiti quinti (ADQ), abductor pollicis brevis (APB), and extensor digitorum btevis muscles. Results: The 3 Hz RNS was abnormal in the ADQ and APB in all patients. Resting CMAP amplitude was most likely to be low in the ADQ (96%). One patient had normal CMAP amplitudes in all muscles. PostMVC CMAP potentiation was most likely to be 2 100% in the ADQ (73%); it was > 100% in at least one muscle in 88% of patients. Trapezius muscles were tested in 5 patients. Decrement to 3 Hz RNS was abnormal in all; CMAP potentiation exceeded 100% only in two. Conclusions: Decrement to 3 Hz RNS in a hand muscle is me most frequent abnormality in LEMS and thus is the most useful screening test. Clinical correlation and measurements of post-MVC CMAP potentiation in multiple muscles are necessary to distinguish LEMS from myasthenia gravis. 14. Familial limb girdle myasthenia. - D.A. Rrendel (The Emory Clinic, Atlanta, GA) A 30-year-old woman had lower extremity weakness and fatigue for 12 years and had been unable to lift small children. Facial and extraocular
Electroencephalography and clinical Neurophysiology 98 (1996) 8P-4OP
Objective: To assess extent and type of injury and natural history in birth-related brachial plexus injury in the neonatal period using electrodiagnostic studies. Methods: Nerve conduction! studies and electromyographic examination were performed at the age of 2 weeks on neonates with clinical diagnosis of Erb’s palsy soon after birth. Follow-up studies were performed on infants who did show sustained clinical improvement. Results: Between October 1993 and January 1995, 13 neonates were diagnosed with Erb’s palsy. Ten neonates had evidence of axonal injury to the upper trunk and 5 had additional injury to the middle trunk as well. Three neonates had neurapraxia and full recovery occurred in 2 weeks. Repeat studies were performed on 3 cases and reinnervation was seen in all previously denervated muscles including those with no voluntary units on initial studies. In 5 cases, repeat examination was not performed as significant recovery had occurred. Conclusion: This study shows that the injury in neonatal Erb’s palsy involves the middle trunk frequently in addition to the upper hunk. Despite evidence of Severe axonal injury on the initial study, significant improvement occurred in all wilh conservative management. 5. Medial antebrachial nerve studies in true neurogenic thoracic outlet syndrome. - J.R. Beattie and M.A. Ross (University of Iowa Hospitals, Iowa City, IA) True neurogenic thoracic outlet syndrome (TOS) is a rare disorder in which electrodiagnostic studies (EDXS) localize the lesion to the lower trunk of the brachial plexus. Medial antebrachial (MA) nerve conduction studies in true neurogenic TOS have not been frequently reported. A 46-year-old man experienced intrinsic hand and left thenar muscle atrophy, and sensory loss involving the left fourth and fifth fingers, and the medial hand and forearm. EDX:S revealed normal amplitude left ulnar compound muscle action potential (CMAP) and median sensory nerve action potential (SNAP), absent left ulnar SNAP, and low amplitude median CMAP. The left MA SNAP was absent, but normal on the right. Needle examination revealed fibrillation potentials in the left abductor pollicis brevis and first dorsal interosseous. The left biceps, triceps and cervical paraspinal muscles were normal. A cervical spine film revealed bilateral cervical ribs, with left more prominent. This patient’s EDXS are typical of true neurogenic TOS. The absent MA SNAP confirms localization of the true neurogenic TOS lesion to the lower trunk of the brachial plexus,.as the MA nerve arises distal to the lower trunk, from the medial cord of the brachial plexus. Additional studies of the MA nerve in other cases of true neurogenic TOS will be useful to determine if this is a consistent finding. 6. Tom Dooley’s syndrome: head hanging from idiopathic cervical plexitis. - P. Wright, W.L. Bell, J. Koufman and F.O. Walker (Bowman Gray School of Medicine, Winston-Salem, NC) Subacute weakness of neck extensors commonly signifies myasthenia gravis, inflammatov myopathy, or botulism. We describe an unusual case of head hanging that resembles idiopathic brachial plexitis. A 46-year-old man developed dyspnea and transient bilateral shoulder pain. Orthopnea, hoarseness and neck extensor weakness followed, causing him to seek medical advice. Examination revealed profound, but painless weakness of neck extension, orthopnea, and paradoxical ventilation. Needle examination revealed marked fibrillation potentials and decreased recruitment of long duration, low amplitude motor units in diaphragm, laryngeal muscles, stemothyroid, splenius capitis, and bilateral C2-5 cervical pamspinal muscles. Diagnostic work-up, including imaging studies, was unremarkable with the exception of fluoroscopically proven bilateral diaphragmatic pamlysis and vocal cord paralysis by fiber optic exam. Escaping the fate of Tom Dooley, who was “bound to die,” the patient gradually regained the ability to hold his head upright and his forced vital capacity increased from 2.1 to 3.3 liters. We believe that Tom
9P
Dooley’s syndrome, head hanging, hoarseness, shoulder pain, and orthopnea, defines a syndrome of idiopathic cervical plexitis. We speculate that it bridges a spectrum of related idiopathic syndromes which include phrenic nerve paralysis, laryngeal paralysis, and brachial plexitis. 7. Central H-reflex latency from Sl root stimulation. I. Intraspinal conduction time of Sl root. - P.Y. Zhu, A. Starr, S. Haldeman and L. Cui (University of California, Irvine, CA) Introduction: We have previously reported that magnetic and percutaneous electrical stimulation of the nerve root elicited soleus H-reflex. This study reports the characteristics of central H-reflex latency (CHL) in a normal population. Objectives: To determine: (I) normal values of CHL; (2) the length of the Sl root; (3) effect on CHL of ischemia of the sciatic nerve; and (4) the clinical usefulness of CHL. Methods and results: (I) We tested 30 men and 30 women (aged 19-62 years). The Sl root was stimulated at the Sl foramen by high voltage electrical stimulation (60 cases) and magnetic stimulation (30 cases). Muscle responses were recorded from soleus with surface electrodes. CHL was defined as the difference between the peak latencies of the H- and M-waves. The mean of the CHL was 6.8 f 0.41 msec with side-to-side difference of 0.16 f 1.8 msec. There was no significant difference between CHL obtained by two methods of stimulation. (2) In 15 cadavers, the mean length of the Sl dorsal root was 17.5 * 0.3 cm, with an la CV of approximately 67.3 m/set. (3) In 2 normal subjects, ischemia of the sciatic nerve produced by a cuff around the thigh abolished the PTN evoked H-reflex, while the CHL was not altered. (4) In 4 patients with Guillain-BamZ syndrome, disk hemiation, disk hemiation and polyneuropathy, and lumbosacral plexopathy, respectively, CHL showed specific characteristics confirming the diagnosis in each patient. Conclusions: Central H-reflex latency reliably represents the intraspinal conduction time of the Sl root, which is of significant clinical usefulness. 8. Cutaneous silent period abnormalities in the carpal tunnel syndrome. - S.K. Aurora, B.K. Ahmad and T.K. Aurora (Henry Ford Hospital and Health Sciences Center, Detroit, MI) Background: Physiological mechanisms underlying the electromyographic silent period (SP) are unclear. There have been no previous studies on SP in carpal tunnel syndrome (CTS). Methods: Cutaneous SP on stimulating digits 2 and 5 was obtained in 20 healthy volunteers, aged 24-45 (mean 32). and in 19 patients with clinical CTS, aged 25-73 (mean 42). SP onset, duration and end were measured in each of 10 trials and averaged. Patients were classified as having mild, moderate or severe CTS based on nerve conduction studies. Paired r tests were used for statistical analysis. Results: In the 2 patients with severe CTS, digit 2 SP was unobtainable. In control subjects, digit 2 SP mean duration was 36.9 msec (S.D. 10.2). In patients, SP mean duration was 51.8 msec (S.D. 16.6) (P= 0.001). In control subjects, the mean SP end was 113.4 (S.D. 10.05) and in patients the mean SP end was 127.3 msec (S.D. 16.2) (P = 0.005). There were no significant differences in digit 2 SP onset and all measures of digit 5 SP. Conclusion: (1) Cutaneous SP is abnormal in CTS, being absent in severe and prolonged in mild to moderate cases. (2) Cutaneous SP research patients should be screened for CT.% S.K. Aurora, M.D., Junior Member Recognition Award. 9. Preserved cutaneous silent period with absent sensory nerve action potentials in peripheral nerve lesions. - V.M. Scruggs and J.J. Wertsch (Medical College of Wisconsin, Milwaukee, WI) Introduction: In peripheral nerve lesions with absent sensory nerve action potentials (SNAPS), an ability to demonstrate axon continuity would be helpful in surgical planning.
1OP
Society proceedings / Electroencephulography and clinical Neurophysiology 98 (1996) 8P4OP
Objective: The purpose of this study was to explore if the cutaneous silent period (CSP) could be obtained in patients with peripheral nerve lesions who have clinical sensory loss and absent SNAPS. Methods: Three patients with isolated ulnar mononeuropathies were studied. All had absent digital ulnar sensory responses; two had marked motor involvement. The CSP response was elicited by applying electrical stimuli to the little finger with surface EMG recorded from the ipsilateral thenar eminence during mild voluntary contraction. Results: The CSP was present in all 3 patients. The duration of the silent period averaged 58 msec with an average onset of 97 msec in the 2 patients measured. With increasing stimulus intensity, the duration of the silent period increased. In 1 individual, comparison with the contralateral side revealed no major differences. Conclusions: The preservation of the CSP in peripheral nerve lesions with absent SNAPS is of interest for further study of the underlying physiologic mechanisms and its clinical applicability in potential surgical cases. V.M. Scruggs, Junior Member Recognition Award.
10. Factors affecting mixed nerve and cutaneous silent periods. J.M. Shefner and E.L. Logigian (Brigham and Women’s Hospital, Boston, MA)
Introduction: Silent periods (SPs) have been studied with increasing frequency to evaluate central movement disorders. However, it is clear that properties of SPs vary with the experimental conditions. Objectives: We wished to evaluate the duration and latency of mixed nerve and cutaneous SP as stimulus intensity and strength of voluntary contraction were systematically altered. Methods: In 10 normal subjects, SPs were obtained from the first dorsal interosseous muscle with stimulation of digit 5 or the ulnar nerve at the wrist. Strength of voluntary contraction was varied and measured with a strain gauge; stimulus intensity was varied from threshold to 12 x threshold. Results: For both mixed nerve and cutaneous SPs, the latency for resumption of voluntary activity increased with increasing stimulus intensity or with decreased voluntary contraction. For the cutaneous SP, the initial SP latency decreased with increasing stimulus intensity or decreased contraction force. Facilitation and inhibition as measured by force changes also varied with stimulus strength and contraction force. Conclusions: The parameters most frequently measured for the cutaneous and mixed nerve SPs vary systematically with experimental conditions. Careful control of these factors is necessary if SPs are to be used as tools for diagnosis or pathophysiological study.
11. Reversal of neuromuscular blockade in coral snake bites: determination by repetitive nerve stimulation and quantitative EMG. - J.E. Gutierrez and L.F. Villota (Universidad de1 Valle, Cali, Colombia)
a-Bungarotoxin, secreted by coral snakes, binds to the postsynaptic acetylcholine receptor and causes a non-depolarizing neuromuscular blockade. We present the neurophysiological studies of a 26-year-old man admitted to the ICU 8 h after being bitten by a Micrurus mipartita mipartita. Initial examination revealed normal sensation, flaccid quadriplegia, areflexia, diplopia, bilateral ptosis and respiratory arrest requiring mechanical ventilation. On admission, motor and sensory latencies were normal with a 50-60% decrease on compound muscle action potential amplitudes. No F-waves could be recorded. Repetitive stimulation (5 Hz) showed a 29% decrement in amplitude and a 34% decrement in area (5: 1 atea ratio = 66%). Motor unit action potentials (MUAPS) were increased in duration (19.2 f 2.5 msec), phases (5 f 2.1). turns (6 f 1.51,variability (“jiggle”) and decreased in amplitude (I59 f 25 /.~Vuv) and area (235 f 52 pV/ms).
Reversal of the neuromuscular blockade was evident 2 hours after specific hyperimmune serum application. Repetitive nerve stimulation showed a 14% decrement in amplitude and an 11% decrement in area (5: 1 area ratio = 89%). MUAP parameters were as follows: Duration (9.8 f 3.85 msec), phases (2 f 1.3), turns (2 f 1.5), amplitude (590 f I I5 PV), area (1116 f 352 pV/msec). The muscle strength increased dramatically. Based on the results, only one-third of the usual antivenin dosage was given. The patient recovered completely within 8 days. Electrophysiological testing detects the reversal of neuromuscular blockade produced by a-bungarotoxin and helps to determine the appropriate antivenin dosage, diminishing the risk of anaphylactic reactions. 12. The electrophysiologic basis of the ice pack test in myasthenia gravis. - J.A. Brooks, S.J. Oh, G.C. Claussen and T.J. Moskowitz (University of Alabama at Birmingham, Birmingham, AL) Introduction: The ice pack test is a simple aid in the diagnosis of myasthenia gravis. However, the original descriptions of this test did not include electrodiagnostic studies to document electrophysiologic improvement. Objective: To study the effect of the ice pack test on the decremental response in myasthenia gravis. Methods: Two patients with generalized myasthenia gravis and bilateral ptosis, who had positive ice pack tests, underwent repetitive nerve stimulation of one facial nerve. This procedure was performed at room temperature, with eyelid skin temperature between 34’C and 34.5”C. and after applying an ice pack to one eye. Results: The decremental response at 2 Hz stimulation at room temperature was 9.3% in patient 1 and 80% in patient 2, improving to 5.7% and 37%. respectively, after application of the ice pack. Improvement of ptosis also occurred in both patients. Conclusion: The ice pack test produces electrophysiologic as well as clinical improvement in myasthenia gmvis. J.A. Brooks, Junior Member Recognition Award. 13. Frequency and distribution of EMG fmdings in Lambert-Eaton myasthenic syndrome. - R.W. Tii, D.B. Sanders and J.M. Massey (Duke University Medical Center, Durham, NC) Objectives: To determine the distribution of abnormality, and to see which test was most likely to demonstrate abnormality in the Lambert-Eaton myasthenic syndrome (LEMS). Methods: In 26 clinically diagnosed LEMS patients, compound motor action potential (CMAP) amplitude, decrement to 3 Hz repetitive nerve stimulation (RNS), and potentiation of CMAP amplitude after maximum voluntary contraction (MVC) were measured in the abductor digiti quinti (ADQ), abductor pollicis brevis (APB), and extensor digitorum btevis muscles. Results: The 3 Hz RNS was abnormal in the ADQ and APB in all patients. Resting CMAP amplitude was most likely to be low in the ADQ (96%). One patient had normal CMAP amplitudes in all muscles. PostMVC CMAP potentiation was most likely to be 2 100% in the ADQ (73%); it was > 100% in at least one muscle in 88% of patients. Trapezius muscles were tested in 5 patients. Decrement to 3 Hz RNS was abnormal in all; CMAP potentiation exceeded 100% only in two. Conclusions: Decrement to 3 Hz RNS in a hand muscle is me most frequent abnormality in LEMS and thus is the most useful screening test. Clinical correlation and measurements of post-MVC CMAP potentiation in multiple muscles are necessary to distinguish LEMS from myasthenia gravis. 14. Familial limb girdle myasthenia. - D.A. Rrendel (The Emory Clinic, Atlanta, GA) A 30-year-old woman had lower extremity weakness and fatigue for 12 years and had been unable to lift small children. Facial and extraocular