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Decerebrate posturing misinterpreted as seizure activity
Decerebrate Posturing Misinterpreted as Seizure Activity STEPHEN J. HAINES, MD Sudden onset of tonic muscular contraction and loss of consciousness is most often caused by an epileptic seizure. In a seizure, however, the tonic muscular contraction is usually followed by interrupted jerking movements. When the motor pattern remains one of tonic contraction, a different underlying mechanism implying a separate differential diagnosis and therapeutic plan must be considered. Failure to make this distinction clearly may lead to neurologic catastrophe. CASE REPORTS Case1 A 42-year-old woman underwent resection of an acoustic neuroma. The operation proceeded without incident, and she was awake, fully responsive, and neurologically normal in the intensive care unit. She suddenly stiffened and lost consciousness. The surgeon was informed by telephone that she had had a seizure. Phenytoin (Dilantin, Park-Davis) was ordered. When she was examined 5 minutes later, she was found to be unresponsive with extensor posturing of the arms, neck, and legs, which was then interpreted as decerebrate posturing. The surgical wound was tense and oozing blood. It was opened immediately, and an epidural hematoma evacuated. The patient immediately regained consciousness and was left with a mild neurologic deficit.
Case2 A 9-year-old girl had been vomiting after meals for 4 months. She had also become morose and withdrawn. Physical and neurologic examinations did not reveal focal neurologic deficit or papilledema. After a thorough gastrointestinal evaluation, she was diagnosed as having anorexia nervosa and was admitted to a psychiatric hospital. Tube feedings were begun. Because she became very agitated during these
feedings, droperidol was administered prior to each feeding. After several weeks of this regimen, 1.75 hours after the administration of droperidol, she acutely became unresponsive with stiffening of all four extremities, arching of the neck, and fixed dilation of both pupils. Within 15 minutes, she regained consciousness and was talking. A similar episode occurred a short time later and again resolved spontaneously. The first episode was interpreted as a reaction to droperidol; the second, as a possible seizure. A third episode occurred 5 hours after the first and progressed to respiratory arrest. She was treated with endotracheal intubation, hyperventilation, and intravenous mannitol and was transferred to a neurosurgical center. There, a computed tomographic (CT) scan of the head (Fig. 1) showed obstructive hydrocephalus and a midline cerebellar mass. A ventriculoperitoneal shunt was placed, but the patient died several days later. Postmortem examination revealed a glioblastoma of the cerebellum.
Case3 A 32.year-old woman, who had been diagnosed as having migraine headaches, came to an emergency department complaining of excruciating headache. Her neurologic and general physical findings were normal, and no papilledema was noted. She was given oral meperidine and sent home. She returned several hours later complaining that the headache persisted. While waiting to be examined, she acutely became confused and incontinent of urine. She was then examined and, during the examination, suddenly developed extensor rigidity of all four extremities and arching of the back and neck. She was unconscious and incontinent. The condition was diagnosed as status epilepticus, and a neuroiogist was consulted. He supervised the administration of an intravenous loading dose of 1200 mg of phenytoin (Dilantin) over approximately 1 hour. A CT scan was then obtained (Fig. 2) which showed obstructive hydrocephalus secondary to a colloid cyst of the third ventricle. Despite immediate bilateral ventriculostomy, the patient died.
Case4 From the Department of Neurosurgery, Minneapolis, Minnesota. Manuscript gust 1987. Address surgery, Building,
received
21 January
University
1987; revision
of Minnesota,
accepted
reprint requests to Dr. Haines: Department University of Minnesota, Box 590, Mayo Minneapolis, MN 55455.
Key Words: Decerebrate posturing, cranial pressure, reactive extensor 0 1988 W.B. Saunders 0735-6757188
Company
50.00 + .25
3 Au-
of NeuroMemorial
differential diagnosis, intrapostural synergy, seizures.
A 15-month-old boy was seen in an emergency department because of lethargy and irritability. He had fallen 2 days previously but had not lost consciousness. He was noted to be febrile, tired but alert, and to have normal neurologic findings. General physical examination revealed an inflamed tympanic membrane with decreased mobility. Papilledema was not noted. Otitis media was diagnosed and an antibiotic prescribed. He was sent home. He was brought back to the emergency department the next day because his parents thought he had had two seizures. He was again febrile, vomiting, and arousable only to 173
AMERICAN
JOURNAL
OF EMERGENCY
MEDICINE
W Volume 6, Number 2
n March 1988
A CT scan showed enlarged ventricles consistent with malfunction of the ventriculoperitoneal shunt. Despite administration of dexamethasone and mannitol and a ventriculostomy (which showed the intracranial pressure to exceed 400 mm cerebrospinal fluid), he died.
DISCUSSION
FIGURE 1. Case 2. Computed tomographic scan showing obstructive hydrocephalus and a large posterior fossa mass distorting the fourth ventricle.
painful stimulation with sluggishly reactive pupils and a stiff neck. During the examination, he suddenly developed tonic upward deviation of the eyes, tonic extension of all extremities, and arching of the back. This lasted a few minutes and recurred several times. The episodes were interpreted as seizures secondary to meningitis. He was treated with anticonvulsant medication, and a lumbar puncture was performed. His condition did not improve, and 7 hours after admission a CT scan was done (Fig. 3). This showed massive obstructive hydrocephalus with hemorrhage in the cerebellar vermis and splenium of the corpus callosum. Neurosurgical consultation was then obtained. Despite immediate ventriculos-
Each of these patients suffered a sudden neurologic deterioration manifested by loss of consciousness with marked increase in extensor tone throughout the body. The posture assumed by these patients was that classically described as “decerebrate.” In each, this sudden alteration in motor activity was interpreted as a seizure, leading to inappropriate treatment. Three of these patients had entirely benign lesions, and one had a tumor that could potentially have been cured or put into long-term remission. In only one of these patients was the catastrophic clinical deterioration recognized as something other than a seizure early enough in the clinical course to allow successful treatment. In the others, confusion of transient decerebrate posturing with seizure activity was followed by death. Several of the cases emphasized the importance of computed tomographic (CT) scanning in evaluating new-onset neurologic signs or symptoms, especially prior to invasive diagnostic tests such as lumbar puncture. However, diffusely increased intracranial pressure may be present without focal neurologic abnormality or papilledema, and its diagnosis is at times diffkult for the nonneurologist. A standard neurology text describes generalized seizures as follows: “The first motor manifestation of the convulsion proper is usually a phase of tonic spasm of the muscles [which] gives place to sharp, short, inter-
tomy, he never regained consciousness. Postmortem examination revealed a cerebellar medulloblastoma. Case 5 A 2-year-old boy had had a ventriculoperitoneal shunt placed at 8 weeks of age because of hydrocephalus. The shunt was revised once for infection and twice for malfunction. He developed febrile seizures during the second year of life. Sixteen months after his last shunt revision, he had two focal seizures and was hospitalized. While under observation, he became lethargic, vomited, and was noted to have several episodes of tonic extension in the legs associated with flexion of the arms and labored respiration. These spells were interpreted as seizures, treated with diazepam, and seemed to resolve. The next morning, while he was being transported to his neurosurgeon’s hospital in his parents’ car, he developed opisthotonic posturing. He was taken back to the original hospital, where he was treated for presumed status epilepticus and then transported to the neurosurgeon by ambulance. By the time of arrival, both pupils were dilated and neither reacted to light. The patient was flaccid. There was no notation in the record regarding papilledema. 174
FIGURE 2. Case 3. Computed tomographic scan showing obstructive hydrocephalus and a colloid cyst at the formanina of Monro.
HAINES n DECEREBRATE POSTURING
FIGURE 3. Case 4. Computed tomographic scan showing hydrocephalus and a hemorrhagic mass in the region of the quadrigeminal plate.
rupted jerks.“’ A typical description of the decerebrate posture, on the other hand, is: “Marked extensor rigidity involving all extremities, occasionally head extension, adduction of the legs and pronation of the arms.“2 Although the descriptions appear to be distinctive, one can see that there might be confusion in the first few minutes before the interrupted tonicclonic activity of the generalized seizure begins. In the International Classification of the Epilepsies, such an episode must fall into the group of generalized seizures.3 Of the subcategories of generalized seizure, only tonic seizures would seem likely candidates for confusion with decerebration. All other categories include clinically distinctive features. Tonic seizures may be classified as tonic-axial, axorhizomelic, or global.4 Tonic-axial seizures are described as showing fixation of the head in the neutral position (flexion or extension is unusual but possible), elevation of the eyebrows, and upward rolling of the eyes associated with rapid shallow breathing. The extremities are not involved. The description of axorhizomelic seizures adds shrugging of the shoulders and abduction and flexion of the arms and occasionally legs. This sort of “hand-up” position is not reminiscent of the decerebrate posture. The global tonic seizure is described as showing the previous signs with the arms pulled up, semiflexed in front of the head with the fists clenched. There is occasional extension of the legs. Gastaut, who has been instrumental in describing tonic seizures, says that they are “never associated with extension of the upper limbs which
together would give the characteristic body attitude of opisthotonus encountered at the end of the tonic phase of tonic-clonic seizures, during decerebrate rigidity or during the tonic attacks of ischemic origin associated with intracranial hypertension.” Tonic seizures do not customarily imitate decerebrate posturing and should not be confused with it. Even if we admit some variability in clinical expression, and therefore the possibility that an atypical tonic seizure could look like decerebration, these are rare seizures. They are seen primarily in LennoxGastaut syndrome and are frequently associated with petit ma1 variant seizures. In an analysis of the prevalence of various forms of epilepsy performed by Lennox in 19605 (using an older classification of seizures), less than 3% of patients had a form of seizure other than grand mal, petit mal, or psychomotor. Therefore, a tonic seizure mimicking decerebrate posturing must be considered an extraordinary event. How often is decerebrate posturing caused by seizures? The differential diagnosis of decerebrate posturing given by Plum and Posner6 does not even mention seizures. Brown and coworkers’ studied 64 infants and children showing signs of decerebration, eliminating from the study patients with head injury, myelomeningocele, or brain tumors. Their classilication of etiology showed 30% of the children had decerebrate episodes related to intracranial hemorrhage, 30% to infection, 18% to hypoxia, 14% to metabolic causes, and 6% to miscellaneous causes that did not include seizures. In 87% of their patients, there was evidence of increased intracranial pressure; 64% of the patients also had seizures during the course of their illness, but these were said to be clearly distinguishable from episodes of decerebration. Ingvar and Lundberg,* in the course of an extensive study of intracranial pressure, simultaneously monitored electroencephalographs (EEG) and intracranial pressure in patients having episodes of decerebration.’ They found that these patients had marked elevations in intracranial pressure associated with spells of decerebration but did not have any evidence of epileptic or paroxysmal cortical discharge on their EEG. They did have one patient who experienced a very typical tonic-clonic seizure during an episode of increased intracranial pressure without evidence of electrical seizure activity. These data would lead one to conclude that if anything is to be suspected when episodic decerebrate posturing is seen, it should be increased intracranial pressure rather than seizure activity. The term cerebellar fit or cerebellar convulsion crept into the literature in the latter part of the 19th century. Jackson’ is generally credited with originating the concept, although his description was of “tetanus-like seizures in a patient with a tumor of the mid175
AMERICAN
JOURNAL
OF EMERGENCY
MEDICINE
n Volume 6, Number 2 n March 1988
dle lobe of the cerebellum.” The earliest use of the term cerebellar firs that I find is in a 1905 article by Charles Dana” describing the syndrome as typical of cerebellar tumors and freely referring to Jackson. The initial use of the termsfit, convulsion, and seizure was simply to describe a physical event. Subsequently, they have been restricted to mean sudden, excessive, disorderly discharge of cerebral neurons. The accurate physical description by Jackson and his contemporaries does not correspond to the physiologic explanation implied by the more recent and restricted meaning of the words. Throughout the literature, however, it has been clearly recognized that the mechanism producing transient decerebrate posturing is not that of epilepsy. Webster and Weinberger” point out the strong association of decerebrate posturing with increased intracranial pressure and suggest that the episodes are probably caused by transient interference with cortical influences on the brainstem. Neidermeyer” states, “ ‘Cerebellar fits’ denote a time honored term for tonic posturing occurring in decerebrate states with mesencephalic release mechanisms. There is no place for these attacks in modern epileptology.” There is argument in the literature as to whether or not transient episodes of decerebrate posturing should be considered equivalent to decerebrate rigidity. Because the classic concept of decerebrate rigidity evolved from animal experimentation, is precisely related to surgical transections of the brainstem at certain levels, and requires testing of various postural reflexes and the establishment of persisting changes in muscle tone, some argue that it is inappropriate to consider transient episodes of decerebrate posturing to be decerebrate rigidity. Close examination of the literature, however, indicates that a rigidly fixed extensor posture is unusual even in experimental animals and, when present, can usually be attributed to factors in addition to midbrain transection. Feldman13 has argued that upper brain stem dysfunction merely lowers the threshold of excitation of intrinsic synergistic extensor reflexes, making it easy to elicit this “reactive extensor postural synergy” with a variety of noxious, postural, and metabolic stimuli. Some animals and humans with midbrain damage subjected to nearly constant noxious stimulation or metabolic stimuli, such as hypoxia or subarachnoid hemorrhage, may have essentially continuous extensor posture or “decerebrate rigidity.“i4 These characteristics of reactive extensor postural synergy (tonic extension of the legs with extension or flexion of the arms, elicitable with appropriate stimuli) should allow the clinical distinction from seizures. Continuous or frequently repeated episodes of extensor posturing are unlikely to be seizures because tonic 176
status epilepticus is extremely rare. A single episode of extensor posturing may be more difficult, but it should be possible to elicit the transient posture with noxious or postural (forced head turning or extension) stimuli. Tonic seizures would rarely be elicitable in this way. CONCLUSIONS The sudden onset of abnormal motor activity associated with loss of consciousness does not always imply that a seizure. Careful but rapid evaluation of the type of motor abnormality allows consideration of other causes, such as increased intracranial pressure or posterior fossa mass lesions. Seizures imply one set of differential diagnoses and allow, except in the case of status epilepticus, a slightly less rapid pace of diagnostic workup. Decerebrate posturing suggests a very different set of differential diagnoses, is highly suggestive of increased intracranial pressure, and therefore contraindicates lumbar puncture and demands immediate evaluation. In this circumstance, evaluation and treatment must proceed simultaneously. In some situations, such as the postoperative patient or one with known hydrocephalus, immediate surgical intervention (such as was done in Case 1) or placement of a ventriculostomy may be indicated. In the patient without a known diagnosis, immediate measures to treat the presumed increased intracranial pressure, including intubation with hyperventilation and osmotic therapy with mannitol(1 g/kg), should be instituted while an immediate CT scan is obtained. Careful observation of the abnormal motor pattern and simple bedside testing should allow the distinction between seizures and decerebrate posturing, enabling the physician to recognize transient decerebration and to diagnose and treat its cause before irreversible neurologic damage occurs. REFERENCES 1. Walton JN: Brain’s Oxford, England, 1103
Diseases of the Nervous System, ed 8. Oxford University Press, 1977, pp 1102-
2. Davis RE, Davis L: Decerebrate surgery 1982;10:635-642
rigidity
in humans.
Neuro-
3. Driefuss FE, Bancaud J, Henriksen 0, et al: Proposal for revised clinical and electroencephalographic classification of epileptic seizures. Epilepsia 1981;22:48!+501 4. Gastaut H, Broughton R, Roger J, et al: Convulsive seizures. In Vinken PJ, Bruyn GW (eds): Handbook of Clinical Neurology, vol 15. Amsterdam, North Holland Publishing Company, 1974, pp 116-l 29 5. Lennox WG: Epilepsy and Related Brown & Co., 1960, p 347
Disorders.
6. Plum F, Posner JB: The Diagnosis of Stupor 3. Philadelphia, Davis, 1980, p 69
Boston,
Little,
and Coma, ed
HAINES n DECEREBRATE
7. Brown JK, Ingram TTS, Seshia SS: Patterns of decerebration in infants and children: defects in homeostasis and sequelae. J Neurol Neurosurg Psychiatry 1973;36:431444 8. lngvar DH, Lundberg N: Paroxysmal symptoms in intracranial hypertension, studied with ventricular fluid pressure recording and electroencephalography. Brain 1961;84: 446-459 9. Jackson JH: Case of tumor of the middle lobe of the cerebellum-cerebellar paralysis with rigidity (cerebellar attitude)-occasional tetanus-like seizures. Brain 1906;29: 425-445
POSTURING
10. Dana CL: The cerebellar seizure (cerebellar fits): a syndrome characteristic of cerebellar tumors. NY Med J/Phila Med J 1905;81:270-272 11. Webster JE, Weinberger LM: Convulsions associated with tumors of the cerebellum. Arch Neurol Psychiatry 1940;43:1163-1184 12. Niedermeyer E: A Compendium of the Epilepsies. Springfield, IL, Charles C Thomas, 1974, p 643 13. Feldman MH: The decerebrate state in the primate: I. Studies in monkeys. Arch Neurol 1971;25:501-516 14. Feldman MH, Sahrmann S: The decerebrate state in the primate: II. Studies in man. Arch Neurol 1971;25:517-525
177
Case2 A 9-year-old girl had been vomiting after meals for 4 months. She had also become morose and withdrawn. Physical and neurologic examinations did not reveal focal neurologic deficit or papilledema. After a thorough gastrointestinal evaluation, she was diagnosed as having anorexia nervosa and was admitted to a psychiatric hospital. Tube feedings were begun. Because she became very agitated during these
feedings, droperidol was administered prior to each feeding. After several weeks of this regimen, 1.75 hours after the administration of droperidol, she acutely became unresponsive with stiffening of all four extremities, arching of the neck, and fixed dilation of both pupils. Within 15 minutes, she regained consciousness and was talking. A similar episode occurred a short time later and again resolved spontaneously. The first episode was interpreted as a reaction to droperidol; the second, as a possible seizure. A third episode occurred 5 hours after the first and progressed to respiratory arrest. She was treated with endotracheal intubation, hyperventilation, and intravenous mannitol and was transferred to a neurosurgical center. There, a computed tomographic (CT) scan of the head (Fig. 1) showed obstructive hydrocephalus and a midline cerebellar mass. A ventriculoperitoneal shunt was placed, but the patient died several days later. Postmortem examination revealed a glioblastoma of the cerebellum.
Case3 A 32.year-old woman, who had been diagnosed as having migraine headaches, came to an emergency department complaining of excruciating headache. Her neurologic and general physical findings were normal, and no papilledema was noted. She was given oral meperidine and sent home. She returned several hours later complaining that the headache persisted. While waiting to be examined, she acutely became confused and incontinent of urine. She was then examined and, during the examination, suddenly developed extensor rigidity of all four extremities and arching of the back and neck. She was unconscious and incontinent. The condition was diagnosed as status epilepticus, and a neuroiogist was consulted. He supervised the administration of an intravenous loading dose of 1200 mg of phenytoin (Dilantin) over approximately 1 hour. A CT scan was then obtained (Fig. 2) which showed obstructive hydrocephalus secondary to a colloid cyst of the third ventricle. Despite immediate bilateral ventriculostomy, the patient died.
Case4 From the Department of Neurosurgery, Minneapolis, Minnesota. Manuscript gust 1987. Address surgery, Building,
received
21 January
University
1987; revision
of Minnesota,
accepted
reprint requests to Dr. Haines: Department University of Minnesota, Box 590, Mayo Minneapolis, MN 55455.
Key Words: Decerebrate posturing, cranial pressure, reactive extensor 0 1988 W.B. Saunders 0735-6757188
Company
50.00 + .25
3 Au-
of NeuroMemorial
differential diagnosis, intrapostural synergy, seizures.
A 15-month-old boy was seen in an emergency department because of lethargy and irritability. He had fallen 2 days previously but had not lost consciousness. He was noted to be febrile, tired but alert, and to have normal neurologic findings. General physical examination revealed an inflamed tympanic membrane with decreased mobility. Papilledema was not noted. Otitis media was diagnosed and an antibiotic prescribed. He was sent home. He was brought back to the emergency department the next day because his parents thought he had had two seizures. He was again febrile, vomiting, and arousable only to 173
AMERICAN
JOURNAL
OF EMERGENCY
MEDICINE
W Volume 6, Number 2
n March 1988
A CT scan showed enlarged ventricles consistent with malfunction of the ventriculoperitoneal shunt. Despite administration of dexamethasone and mannitol and a ventriculostomy (which showed the intracranial pressure to exceed 400 mm cerebrospinal fluid), he died.
DISCUSSION
FIGURE 1. Case 2. Computed tomographic scan showing obstructive hydrocephalus and a large posterior fossa mass distorting the fourth ventricle.
painful stimulation with sluggishly reactive pupils and a stiff neck. During the examination, he suddenly developed tonic upward deviation of the eyes, tonic extension of all extremities, and arching of the back. This lasted a few minutes and recurred several times. The episodes were interpreted as seizures secondary to meningitis. He was treated with anticonvulsant medication, and a lumbar puncture was performed. His condition did not improve, and 7 hours after admission a CT scan was done (Fig. 3). This showed massive obstructive hydrocephalus with hemorrhage in the cerebellar vermis and splenium of the corpus callosum. Neurosurgical consultation was then obtained. Despite immediate ventriculos-
Each of these patients suffered a sudden neurologic deterioration manifested by loss of consciousness with marked increase in extensor tone throughout the body. The posture assumed by these patients was that classically described as “decerebrate.” In each, this sudden alteration in motor activity was interpreted as a seizure, leading to inappropriate treatment. Three of these patients had entirely benign lesions, and one had a tumor that could potentially have been cured or put into long-term remission. In only one of these patients was the catastrophic clinical deterioration recognized as something other than a seizure early enough in the clinical course to allow successful treatment. In the others, confusion of transient decerebrate posturing with seizure activity was followed by death. Several of the cases emphasized the importance of computed tomographic (CT) scanning in evaluating new-onset neurologic signs or symptoms, especially prior to invasive diagnostic tests such as lumbar puncture. However, diffusely increased intracranial pressure may be present without focal neurologic abnormality or papilledema, and its diagnosis is at times diffkult for the nonneurologist. A standard neurology text describes generalized seizures as follows: “The first motor manifestation of the convulsion proper is usually a phase of tonic spasm of the muscles [which] gives place to sharp, short, inter-
tomy, he never regained consciousness. Postmortem examination revealed a cerebellar medulloblastoma. Case 5 A 2-year-old boy had had a ventriculoperitoneal shunt placed at 8 weeks of age because of hydrocephalus. The shunt was revised once for infection and twice for malfunction. He developed febrile seizures during the second year of life. Sixteen months after his last shunt revision, he had two focal seizures and was hospitalized. While under observation, he became lethargic, vomited, and was noted to have several episodes of tonic extension in the legs associated with flexion of the arms and labored respiration. These spells were interpreted as seizures, treated with diazepam, and seemed to resolve. The next morning, while he was being transported to his neurosurgeon’s hospital in his parents’ car, he developed opisthotonic posturing. He was taken back to the original hospital, where he was treated for presumed status epilepticus and then transported to the neurosurgeon by ambulance. By the time of arrival, both pupils were dilated and neither reacted to light. The patient was flaccid. There was no notation in the record regarding papilledema. 174
FIGURE 2. Case 3. Computed tomographic scan showing obstructive hydrocephalus and a colloid cyst at the formanina of Monro.
HAINES n DECEREBRATE POSTURING
FIGURE 3. Case 4. Computed tomographic scan showing hydrocephalus and a hemorrhagic mass in the region of the quadrigeminal plate.
rupted jerks.“’ A typical description of the decerebrate posture, on the other hand, is: “Marked extensor rigidity involving all extremities, occasionally head extension, adduction of the legs and pronation of the arms.“2 Although the descriptions appear to be distinctive, one can see that there might be confusion in the first few minutes before the interrupted tonicclonic activity of the generalized seizure begins. In the International Classification of the Epilepsies, such an episode must fall into the group of generalized seizures.3 Of the subcategories of generalized seizure, only tonic seizures would seem likely candidates for confusion with decerebration. All other categories include clinically distinctive features. Tonic seizures may be classified as tonic-axial, axorhizomelic, or global.4 Tonic-axial seizures are described as showing fixation of the head in the neutral position (flexion or extension is unusual but possible), elevation of the eyebrows, and upward rolling of the eyes associated with rapid shallow breathing. The extremities are not involved. The description of axorhizomelic seizures adds shrugging of the shoulders and abduction and flexion of the arms and occasionally legs. This sort of “hand-up” position is not reminiscent of the decerebrate posture. The global tonic seizure is described as showing the previous signs with the arms pulled up, semiflexed in front of the head with the fists clenched. There is occasional extension of the legs. Gastaut, who has been instrumental in describing tonic seizures, says that they are “never associated with extension of the upper limbs which
together would give the characteristic body attitude of opisthotonus encountered at the end of the tonic phase of tonic-clonic seizures, during decerebrate rigidity or during the tonic attacks of ischemic origin associated with intracranial hypertension.” Tonic seizures do not customarily imitate decerebrate posturing and should not be confused with it. Even if we admit some variability in clinical expression, and therefore the possibility that an atypical tonic seizure could look like decerebration, these are rare seizures. They are seen primarily in LennoxGastaut syndrome and are frequently associated with petit ma1 variant seizures. In an analysis of the prevalence of various forms of epilepsy performed by Lennox in 19605 (using an older classification of seizures), less than 3% of patients had a form of seizure other than grand mal, petit mal, or psychomotor. Therefore, a tonic seizure mimicking decerebrate posturing must be considered an extraordinary event. How often is decerebrate posturing caused by seizures? The differential diagnosis of decerebrate posturing given by Plum and Posner6 does not even mention seizures. Brown and coworkers’ studied 64 infants and children showing signs of decerebration, eliminating from the study patients with head injury, myelomeningocele, or brain tumors. Their classilication of etiology showed 30% of the children had decerebrate episodes related to intracranial hemorrhage, 30% to infection, 18% to hypoxia, 14% to metabolic causes, and 6% to miscellaneous causes that did not include seizures. In 87% of their patients, there was evidence of increased intracranial pressure; 64% of the patients also had seizures during the course of their illness, but these were said to be clearly distinguishable from episodes of decerebration. Ingvar and Lundberg,* in the course of an extensive study of intracranial pressure, simultaneously monitored electroencephalographs (EEG) and intracranial pressure in patients having episodes of decerebration.’ They found that these patients had marked elevations in intracranial pressure associated with spells of decerebration but did not have any evidence of epileptic or paroxysmal cortical discharge on their EEG. They did have one patient who experienced a very typical tonic-clonic seizure during an episode of increased intracranial pressure without evidence of electrical seizure activity. These data would lead one to conclude that if anything is to be suspected when episodic decerebrate posturing is seen, it should be increased intracranial pressure rather than seizure activity. The term cerebellar fit or cerebellar convulsion crept into the literature in the latter part of the 19th century. Jackson’ is generally credited with originating the concept, although his description was of “tetanus-like seizures in a patient with a tumor of the mid175
AMERICAN
JOURNAL
OF EMERGENCY
MEDICINE
n Volume 6, Number 2 n March 1988
dle lobe of the cerebellum.” The earliest use of the term cerebellar firs that I find is in a 1905 article by Charles Dana” describing the syndrome as typical of cerebellar tumors and freely referring to Jackson. The initial use of the termsfit, convulsion, and seizure was simply to describe a physical event. Subsequently, they have been restricted to mean sudden, excessive, disorderly discharge of cerebral neurons. The accurate physical description by Jackson and his contemporaries does not correspond to the physiologic explanation implied by the more recent and restricted meaning of the words. Throughout the literature, however, it has been clearly recognized that the mechanism producing transient decerebrate posturing is not that of epilepsy. Webster and Weinberger” point out the strong association of decerebrate posturing with increased intracranial pressure and suggest that the episodes are probably caused by transient interference with cortical influences on the brainstem. Neidermeyer” states, “ ‘Cerebellar fits’ denote a time honored term for tonic posturing occurring in decerebrate states with mesencephalic release mechanisms. There is no place for these attacks in modern epileptology.” There is argument in the literature as to whether or not transient episodes of decerebrate posturing should be considered equivalent to decerebrate rigidity. Because the classic concept of decerebrate rigidity evolved from animal experimentation, is precisely related to surgical transections of the brainstem at certain levels, and requires testing of various postural reflexes and the establishment of persisting changes in muscle tone, some argue that it is inappropriate to consider transient episodes of decerebrate posturing to be decerebrate rigidity. Close examination of the literature, however, indicates that a rigidly fixed extensor posture is unusual even in experimental animals and, when present, can usually be attributed to factors in addition to midbrain transection. Feldman13 has argued that upper brain stem dysfunction merely lowers the threshold of excitation of intrinsic synergistic extensor reflexes, making it easy to elicit this “reactive extensor postural synergy” with a variety of noxious, postural, and metabolic stimuli. Some animals and humans with midbrain damage subjected to nearly constant noxious stimulation or metabolic stimuli, such as hypoxia or subarachnoid hemorrhage, may have essentially continuous extensor posture or “decerebrate rigidity.“i4 These characteristics of reactive extensor postural synergy (tonic extension of the legs with extension or flexion of the arms, elicitable with appropriate stimuli) should allow the clinical distinction from seizures. Continuous or frequently repeated episodes of extensor posturing are unlikely to be seizures because tonic 176
status epilepticus is extremely rare. A single episode of extensor posturing may be more difficult, but it should be possible to elicit the transient posture with noxious or postural (forced head turning or extension) stimuli. Tonic seizures would rarely be elicitable in this way. CONCLUSIONS The sudden onset of abnormal motor activity associated with loss of consciousness does not always imply that a seizure. Careful but rapid evaluation of the type of motor abnormality allows consideration of other causes, such as increased intracranial pressure or posterior fossa mass lesions. Seizures imply one set of differential diagnoses and allow, except in the case of status epilepticus, a slightly less rapid pace of diagnostic workup. Decerebrate posturing suggests a very different set of differential diagnoses, is highly suggestive of increased intracranial pressure, and therefore contraindicates lumbar puncture and demands immediate evaluation. In this circumstance, evaluation and treatment must proceed simultaneously. In some situations, such as the postoperative patient or one with known hydrocephalus, immediate surgical intervention (such as was done in Case 1) or placement of a ventriculostomy may be indicated. In the patient without a known diagnosis, immediate measures to treat the presumed increased intracranial pressure, including intubation with hyperventilation and osmotic therapy with mannitol(1 g/kg), should be instituted while an immediate CT scan is obtained. Careful observation of the abnormal motor pattern and simple bedside testing should allow the distinction between seizures and decerebrate posturing, enabling the physician to recognize transient decerebration and to diagnose and treat its cause before irreversible neurologic damage occurs. REFERENCES 1. Walton JN: Brain’s Oxford, England, 1103
Diseases of the Nervous System, ed 8. Oxford University Press, 1977, pp 1102-
2. Davis RE, Davis L: Decerebrate surgery 1982;10:635-642
rigidity
in humans.
Neuro-
3. Driefuss FE, Bancaud J, Henriksen 0, et al: Proposal for revised clinical and electroencephalographic classification of epileptic seizures. Epilepsia 1981;22:48!+501 4. Gastaut H, Broughton R, Roger J, et al: Convulsive seizures. In Vinken PJ, Bruyn GW (eds): Handbook of Clinical Neurology, vol 15. Amsterdam, North Holland Publishing Company, 1974, pp 116-l 29 5. Lennox WG: Epilepsy and Related Brown & Co., 1960, p 347
Disorders.
6. Plum F, Posner JB: The Diagnosis of Stupor 3. Philadelphia, Davis, 1980, p 69
Boston,
Little,
and Coma, ed
HAINES n DECEREBRATE
7. Brown JK, Ingram TTS, Seshia SS: Patterns of decerebration in infants and children: defects in homeostasis and sequelae. J Neurol Neurosurg Psychiatry 1973;36:431444 8. lngvar DH, Lundberg N: Paroxysmal symptoms in intracranial hypertension, studied with ventricular fluid pressure recording and electroencephalography. Brain 1961;84: 446-459 9. Jackson JH: Case of tumor of the middle lobe of the cerebellum-cerebellar paralysis with rigidity (cerebellar attitude)-occasional tetanus-like seizures. Brain 1906;29: 425-445
POSTURING
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