reflex myoclonic epilepsy in infancy: a new age-dependent idiopathic epileptic syndrome related to...

Epilepsia, 36(4):342-348, 1995 Raven Press, Ltd., New York 0 International League Against Epilepsy

Reflex Myoclonic Epilepsy in Infancy: A New Age-Dependent Idiopathic Epileptic Syndrome Related to

Startle Reaction

Stefan0 Ricci, Raffaella Cusmai, Lucia Fusco, and Federico Vigevano

Section of Neurophysiology, Bambino Gesu Children’s Hospital, I.R.C.C.S., Rome, Italy

Summary: Benign myoclonic epilepsy of infancy (BMEI) is an idiopathic disorder characterized by spontaneous myoclonic attacks with onset in the first 2 years of life. We observed 6 neurologically normal infants (aged 6-21 months) with attacks that resembled those of BMEI but that occurred as reflex responses to unexpected auditory and tactile stimuli. Four infants also had rare spontaneous attacks. These reflex attacks consisted of isolated muscle jerks or clusters of up to eight symmetric limb jerks af- fecting mainly the arms. Five of the children had a family history of epilepsy or febrile convulsions. Myoclonic attacks disappeared in 6 1 4 months. In 3 patients, the jerks

stopped spontaneously; the others responded to valproate (VPA). Myoclonus could be elicited in wakefulness and in sleep. Ictal EEGs showed brief generalized spike- or polyspike-and-wave discharges. Interictal EEGs were normal during wakefulness; during sleep, brief generalized discharges were evident. We propose that reflex myoclonic epilepsy of infancy (RMEI) is a new age- dependent idiopathic generalized epileptic (IGE) syndrome, with an apparently good prognosis. Key Words: Epilepsy-Myoclonus-Startle reaction-Infancy- Reflex epilepsy.

Benign myoclonic epilepsy in infancy (BMEI) (Commission, 1989) is an epileptic syndrome with onset between 6 months and 2 years, characterized by brief myoclonic attacks in otherwise normal infants. BMEI is considered an idiopathic generalized epilepsy (IGE) related to a genetic predisposition. The myoclonic jerks typical of BMEI have always been described as spontaneous; Dravet et al. (1985) reported that BMEI has “no known triggering fac- tor.” Considering it a rare syndrome, they origi- nally found only 17 reported cases, a number that they subsequently increased to 37 (Dravet et al., 1992).

Recent case reports have described children in whom brief myoclonic jerks resembling those of BMEI developed in response to unexpected tactile stimuli, such as sudden touching of the face or trunk (Deonna and Despland, 1989; Revol et al., 1989). The myoclonic jerks responded to valproate (VPA),

Received March 24, 1994; revision accepted August 1 , 1994. Address correspondence and reprint requests to Dr. S. Ricci at

Section of Neurophysiology, Bambino Gesh Children’s Hospi- tal, I.R.C.C.S., Piazza S. Onofrio 4, 00165 Rome, Italy.

Presented in part at the 1993 Annual Meeting of the American Epilepsy Society, Miami, Florida and abstracted in Epilepsia 1994;34(suppl 6):47.

and the researchers classified the disorder as “idiopathic myoclonic epilepsy of very early onset.”

We report a clinical and video-EEG-polygraphic study of 6 children, all of whom had generalized reflex myoclonic jerks starting in the first 2 years of life. This phenomenon merits greater interest because it appears to be the earliest form of idiopathic generalized-onset myoclonic epilepsy.

PATIENTS AND METHODS

The 6 children studied were observed at the Ep- ilepsy Center of the Bambino Gesu Children’s Hos- pital between 1990 and 1993. Clinical characteristics are summarized in Table 1.

All children underwent repeated video-EEG and polygraphic recording during wakefulness and sleep. Electrodes were placed according to the In- ternational 10-20 system. Polygraphic studies included surface electromyographic (EMG) recording from at least two deltoid muscles, and channels for respiration and electrocardiogram. The children also underwent sensory stimulation with multiple unexpected acoustic stimuli (loud and soft noises), unexpected tactile and thermal stimuli (cool water over the face), visual stimuli [intermittent light stim-

342

REFLEX MYOCLONIC ATTACKS IN INFANCY 343

TABLE 1. Clinical characteristics of children with RMEl ~ ~ ~ _ _ _ _

Age at Age of onset of disappearance Duration

Family Psychomotor jerks of jerks of RMEI Spontaneous Other FOIIOW-UP Patientlsex history development (mo) (mo) (mo) jerks seizures Therapy (yr.mo)

1/M CAE (I") Normal 9 13 4 FC - 3.1 21M FC (I"

-

2.1 - - - and 11") Normal 8 12 4 3/F GTC (I") Normal 6 14 8 + - CNP, 1.5

JME (11") VPA 4/F FC (11") Normal 12 24 12 + - VPA 1.2 51M FC (I") Normal 9 16 7 + 6/M - Normal 21 24 3 + VPA 0.8

0.11 - - -

RMEI, reflex myoclonic epilepsy in childhood; CAE, childhood absence epilepsy; FC, febrile convulsions; GTCS, generalized tonic-clonic seizures; JME, juvenile myoclonic epilepsy, I" and II", first- and second-degree relatives; CNP, clonazepam; VPA, valproate.

ulation (ILS) and single, unexpected photo-flashes obtained with a high-powered commercial flash ap- paratus]. Video recordings of the attacks were re- viewed at both normal speed and in slow motion (frame-to-frame) to identify the single components of the events.

Clinical Findings All 6 children were born to healthy unrelated par-

ents after normal pregnancies and deliveries. Psy- chomotor and neurological development were normal. Five had a family history of epilepsy (childhood absence epilepsy, myoclonic epilepsy, tonic- clonic seizures) or of febrile convulsions in first- or second-degree relatives. Neuroradiological and metabolic investigations yielded normal findings in all children. Neurological examinations were normal at the end of follow-up.

Myoclonic jerks appeared between the ages of 6 and 21 months (mean 10.8 months). In all cases, the parents had contacted a neurologist because of an excessive startle response to external stimuli that caused "jumping" of the arms and legs. In 2 children, the myoclonic jerks appeared only in response to sensory stimuli. In the other 4, jerks occurred mostly in response to provocation but sometimes appeared to be spontaneous. Spontaneous attacks generally appeared months after the reflex attacks and were facilitated by sleep and somnolence.

The total number of attacks in each child varied from day to day, depending mostly on the environ- mental precipitants. At the time of the examination by a neurologist, the frequency of attacks usually ranged from 5 to 20 a day.

Because the myoclonic attacks were brief and occurred only as reflex responses, we recommended not treating the children, if their parents agreed. If the attacks persisted >6 months, or when the duration and frequency of the seizures increased, or when bouts of spontaneous jerking became more

frequent, we initiated treatment with VPA. Three children were treated and 3 were not. VPA was administered at low dosages (20-25 mg/kg/day) and stopped the attacks in all cases in s 2 months. One patient (patient 3) received clonazepam for 6 months without benefit.

The duration of the disorder ranged from 4 to 12 months. In 2 of the 3 untreated children the myoclonic jerks disappeared spontaneously 4 months after onset; in the other child, jerks subsided 7 months after onset. At the age of 18 months, patient 1 had a single brief febrile convulsion. Mean duration of follow-up was 18 months (range 8 months to 3 years).

EEG, Video, and polygraphic findings The manifestations consisted of single myoclonic

jerks (Fig. 1) or clusters of as many as eight massive symmetric myoclonic jerks of the arms or the whole body (Fig. 2), with flexion of the head and deviation of upward gaze. Longer series of jerks were characterized by repeated flexion-extension movements of the limbs, predominantly the arms. The brevity of most attacks and the young age of the patients made it hard to assess the level of consciousness which, during longer attacks appeared to be im- paired. Myoclonus was elicitable both in wakefulness and in sleep (Fig. 3). During sleep, the threshold for myoclonus was lower in stage I and increased gradually during the slower stages 11-IV. None of the recordings included rapid eye movement (REM) sleep.

The ictal EEG consisted of generalized high- amplitude spike- or polyspike-and-wave discharges occurring at a frequency of 3 Hz and lasting 0.5-3 s . The discharges were symmetric, with frontocentral predominance. Some discharges, particularly those during sleep, had an irregular pattern (Fig. 3). The EEG polyspikes coincided with brief rhythmic bursts of EMG activity. The limbs were involved symmetrically and proximally, the arms .more than

Epilepsia, Vol. 36, No. 4, 1995

S. RICCI ET AL. 344

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Waking EEGs were normal in all 6 children between attacks. Sleep EEGs were characterized by rare, generalized irregular polyspike-and-wave discharges, usually accompanied by brief and irregular jerks (Fig. 4). The discharges were evident in all the

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FIG. 1. Patient 6. Three similar myoclonic jerks provoked by different stimuli. Left (1): Acoustic stimuli (a noise provoked by a heavy metal l ic object fal l ing to the ground). Center (2): Sensory stimuli (unexpected shock provoked by tapping the right knee with a neurologist's hammer). Right (3): Com- bined tactile and thermic stimuli (briefly spraying water over the face with a small syringe). Arrows: Stimuli.

stages of non-REM sleep, mostly during stages I and 11.

Video films showed that the initial manifestation of the reflex myoclonic attacks occurring during wakefulness generally consisted of a blink, followed 40-80 ms later (one or two video frames) by the first myoclonic arm jerk. Some attacks started without an evident eyeblink, the initial movement being the myoclonus itself. The video films did not show

t t FIG. 2. Patient 6. Three reflex attacks recorded during somnolence. Left: A typical symmetric and rhythmic ictal discharge lasting 2 s. Center: A predominantly left-sided asymmetrical discharge accompanied by an asymmetric electromyographic (EMG) pattern (myoclonic jerks predominantly involve the right arm). Right: A symmetric discharge with pronounced frontal prevalence accompanied by an irregular EMG pattern. Arrows: stimuli (sudden noises).



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FIG. 3. Patient 5. EEG patterns. Left: A myoclonic attack lasting 2.5 s, provoked by a sudden noise during wakefulness, with coincidence of myoclonic jerks with EEG spikes. Right: A myoclonic attack of similar duration during sleep. Arrows: stimuli. In both discharges, the discharge had onset with a negative spike on the vertex (phase reversal in Cz), and the electromyographic pattern progression was craniocaudal. Eyeblink also was evident at the onset of the discharge in wakefulness; no ocular movement was detectable at the onset of the discharge during sleep.

whether the blink was completely absent or was present but incomplete. A brief, weak orbicularis oculi contraction, too small to identify on the video, might have occurred even though the eyes remained open. In reflex attacks recorded during sleep, the eyeblink appeared to be absent (Fig. 3).

After a myoclonic attack, there was a refractory period, lasting 2&30 s to 1-2 min, during which sudden auditory stimuli would not provoke attacks, even when the startle reaction was easily elicitable. Sudden auditory stimuli evoked a vertex negative sharp wave in the EEG with phase reversal at the Cz position. The waveform correlated with the si- multaneous EMG activity. A more indented wave, similar to a low-amplitude polyspike, coincided with a myoclonic EMG burst (Fig. 5). Although 4 children in our series also had spontaneous attacks while awake, we did not record them.

Trigger stimuli Regardless of the type of stimulus used, surprise

appeared fundamental in triggering attacks. If the children expected the stimulus, they did not have an attack.

Acoustic stimuli triggered myoclonic attacks in all 6 children. Four children reacted only in response to loud noises (e.g., heavy metal objects falling to the ground, a door slamming, clapping the hands), whereas 2 children reacted more often to brief soft noises (e.g., those obtained by tearing a paper tissue or causing a small spring to vibrate). Soft noises provoked attacks only in a silent envi- ronment.

During a recording, the threshold for attacks varied according to the ambient noise level, the child's attention level (which increased the threshold), and somnolence (which decreased it). Frequent repeti- tion of stimuli decreased the ictal response.

Even though they provoked attacks in all the children, tactile stimuli were less effective than acoustic stimuli. Sudden touching of the face and the limbs provoked attacks only when the children did not expect the stimulus. The most effective com- bined tactile-thermal stimulus consisted of spraying cool water on the face with a small syringe.

Visual stimuli, including traditional ILS with a high-powered strobe and sudden, unexpected, high- intensity single flashes, did not trigger seizures.


346 S. RICCI ET AL.

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FIG. 4. Patient 5. Three unprovoked brief myoclonic jerks during different stages of sleep. Jerks and discharges during sleep were irregular.

DISCUSSION

In a recent book on reflex seizures and reflex epilepsies, Deonna and Despland (1989) described 2 children who had myoclonic jerks in response to sudden stimuli. In another chapter in the same book, Revol et al. (1989) described 2 other children with reflex myoclonic jerks; the first child had the same manifestations as our subjects. In these three cases, myoclonic jerks occurred in response to touch, but in one they were provoked by tactile and auditory stimuli and later appeared spontaneously.

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t t FIG. 5. Patient 6. EEG/electromyographic effects of two unexpected noises during the postmyoclonic refractory periods (enlargement of eight polygraphic channels). Left: The noise (arrow) evoked a negative sharp wave in Cz position. Right: The prominent myoclonic component coincided with a sharply contoured vertex wave (a low-amplitude polyspike) in Cz position. Arrows: Stimuli.

We found no other published cases with the same features. These three cases and our series of 6 patients allow us to identify a remarkably homoge- neous clinical syndrome, for which we propose the term “reflex myoclonic epilepsy in infancy” (RMEI).

RMEI was probably underdescribed and under- evaluated in the past simply because the attacks are reflex and brief and because they appear in otherwise normal children, thus being misinterpreted as a normal or “slightly excessive” startle reaction. The brevity of the disorder observed by us in some cases also suggests that in some children RMEI may be so brief that it is never diagnosed.

We found only a few sporadic reports of patients with idiopathic generalized nonphotosensitive reflex seizures. De Marco (1990) described a girl with clonic attacks starting at 5 months who subsequently had brief spells triggered by tapping the face. Reflex myoclonic jerks appearing in the first year of life have been reported in children with Down syndrome and reflex epilepsy (Guerrini et al., 1990).

Our patients with RMEI had a benign clinical course: the jerks disappeared rapidly, in 3 children spontaneously and in 3 after VPA therapy. The disorder was strictly age related, reaching a peak at



-10 months. The high incidence of febrile seizures or a family history of epilepsy in our patients (5 of 6) suggests that the syndrome has an idiopathic origin.

Our patients had remarkably similar EEG findings. The typical ictal pattern consisted of brief generalized spike-and-wave or polyspike-and-wave discharges. Interictal EEGs were normal during wakefulness; rare generalized discharges occurred spontaneously or reflexly during sleep. The EEG discharges disappeared when the disorder ceased. These EEG findings clearly indicate a generalized epileptic form.

Because of the typical electroclinical findings of RMEI, the differential diagnosis is straightforward. RMEI must be differentiated from other epileptic and nonepileptic manifestations, however.

Exclusion of the other myoclonic forms of epilepsy is essential in diagnosis. Normal psychomotor development before and after the onset of the attacks , easy multisensorial provocation of seizures, absence of EEG focal or diffuse slowing, absence of interictal focal spikes, absence of atonic or tonic attacks, absence of photosensitivity and, finally, absence of EEG interictal discharges during wakefulness clearly differentiate RMEI from other epileptic syndromes with myoclonic manifestations, such as West syndrome, Lennox-Gastaut syndrome, myoclonic-astatic epilepsy, and severe myoclonic epilepsy.

Despite having in common an excessive startle reaction, RMEI and startle epilepsy are two distinct entities. Startle epilepsy (Gastaut and Tassinari, 1966; Bancaud et al., 1967; Aguglia et al., 1984; Saentz-Lope et al., 1984~; Tassinari et al., 1991; Lancman et al., 1993) is a variable entity characterized by seizures and a startle response to sudden stimuli that occurs across a wide age range (from birth to adult age). It also has diverse clinical and EEG patterns (partial, tonic, atonic, myoclonic, unilateral tonic or atonic, or myoclonic seizures, or combinations of these). Startle epilepsy generally arises from brain damage. The etiology of startle epilepsy includes various conditions, the most frequent being hypoxic-ischemic pre- and perinatal le- sions. The seizures of startle epilepsy are often un- treatable. Rather than being a syndrome, startle epilepsy thus appears to encompass widely differing entities, linked only by the reflex modality of seizure provocation.

Distinctive EEG and EMG findings also differentiate RMEI from nonepileptic manifestations characterized by an excessive startle response. Primary hyperekplexia, also called startle disease (Suhren et al., 1966; Gastaut and Villeneuve 1967; Markand et al., 1984; Saentz-Lope et al., 19846; Andermann

and Andermann, 1986,1988; Vigevano et al., 1989; Brown et al., 1991; Howard and Ford, 1992) is characterized by hypertonia appearing in the first months of life and by falling or tonic attacks in response to sudden stimuli. The EEG does not show epileptic discharges during attacks, although sudden noises may evoke a negative vertex wave followed by a background desynchronization (Suhren et al., 1966; Gastaut and Villeneuve, 1967; Ander- mann and Andermann, 1986,1988) and by tonic EMG activity originating in the frontal muscles and descending to the legs. Despite the differences between the two conditions, startle disease and RMEI have some common features. First, the presence of an eyeblink as the first response to stimuli repre- sents the initial component of the startle reflex (the “early response,” Gogan, 1970). Second, some myoclonic seizures show craniocaudal progression similar to that occurring in the startle reflex (Wilkins et al., 1986). Finally, our patient’s EEG responses to sudden stimuli also showed a negative vertex wave, suggesting hyperactivity of the cortex in response to efferent outputs from the neuronal nuclei responsible for the startle reflex, believed to be in the medial bulbopontine reticular formation of the brainstem (Brown et al., 1991), an area that re- ceives afferent inputs from multiple sensory path- ways.

BMEI and RMEI are rare conditions. Reviewing the literature, Dravet et al. (1992) found only 37 cases published since 1981. RMEI apparently is an even rarer condition, since the present series and the previous published cases comprise only 9 patients. Despite being apparently similar conditions, BMEI and RMEI differ in many ways. Most impor- tant is the complete absence of provoking factors in BMEI, whereas in RMEI such factors are the rule. Moreover, children with RMEI are never referred for atonic seizures (i.e., head drops) or falling attacks, both common in BMEI. RMEI has a shorter duration than BMEI ( s 4 years 9 months for BMEI in the series of Dravet et al., 1992), whereas the mean duration of RMEI in our series was 6 months. In our experience, BMEI also has a longer duration: in 11 patients who had BMEI observed between 1987 and 1993 (unpublished observations), we observed the spontaneous cessation of myoclonic jerks in only 1 patient; all the remaining patients required therapy, and jerks disappeared during a period of 2 years to 3 years 9 months. RMEI appears to have earlier onset than BMEI (onset at 10 months in RMEI, whereas the mean age of onset in our BMEI series was 20 months). Pharmacological treatment (VPA) appears to be more effective in RMEI than in BMEI, and treatment duration may


348 S . RICCI ET AL.

be shorter: patients with BMEI often require long- term treatment. Discontinuing therapy in BMEI may cause seizures to relapse (Todt and Muller, 1992). The genetic predisposition appears to be greater in RMEI than in BMEI (80% in our RMEI series vs. 31% in the BMEI series of Dravet et al., 1992). A male preponderance was evident in both groups (M/F ratio of 4:2 in our subjects).

In our children, RMEI had a benign course, and in all cases the myoclonic attacks disappeared completely. Our maximum 3-year follow-up does not allow us to assess long-term prognosis, however.

The close age-dependency , high genetic predisposition, EEG findings, and normal neurologic development suggest that RMEI constitutes the earliest reflex generalized idiopathic epileptic syndrome, which should be classified as a distinct entity.

Acknowledgment: We thank our technicians Laura Maurizi, Giuseppe Perfetti, Angela Pinna, Paola Mancini, Concetta Brachino, Santina Pinna, Gemma Mazzetti, Lorenza Lucchina, and Mennato Forgione (now at Co- lumbia University in New York) for their invaluable con- tribution and for their patience, inventiveness, and gentle behavior with the children. We are grateful to Dr. Dianela Claps for referring patient 3 and Dr. Maria Roberta Cilio for reyiewing the video of patient 6 . We are also grateful to Roberto Tombari for his technical support with the video films and photographs and to Alice Crossman for her patient and criticism in reviewing the manuscript.

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