Neonatal Hyperekplexia: a case report

Startle disease or hyperekplexia, a rare hereditary neurologic disorder, was first described by Kirstein and Silfverskiold (l958), with subsequent reports of affected families and sporadic cases (Suhren et al., 1966; Andermann et al., 1980; Lingam et al., 1981; Kurczynski, 1983; Markand et al., 1984; Saenz-Lope et al., 1984; Dooley and Andermann, 1989; Brown et al., 1991). The disorder, manifested by an exaggerated startle response, generalized muscular rigidity in infancy and prominent nocturnal myoclonus, is characterized by two abnormal forms of response to unexpected auditory visual, and somaesthetic stimuli: the sustained tonic spasm and the briefer pathologic startle reflex. Both arc presumed to bc the result of activity in a common reflex center in the lower brainstem (Brown et al., 1991). Giant cortical somatosensory evoked potentials (SEPs) have been noted in probands and relatives. Hyperekplexia is easily mistaken for commoner problems such as epilepsy, spastic quadriparesis, ataxia, and myoclonic syndromes. A major and a minor form have been distinguished (Andermann et al., 1980). Symptomatology is dependent on age of onset. The major form, with neonatal onset, can be very severe, with newborns having repeated myoclonic jerks and increased muscle tone with life-threatening apnea due to contraction of respiratory muscles. Two sudden infant deaths have been reported (Suhren et al., 1966; Kurczynski, 1983; Vigevano et al., 1989). We report a 30-day-oId baby with startle disease and a family history of hyperekplexia.

CASE REPORT

A male infant was born at term after a normal pregnancy with a birthweight of 3,150g and an Apgar score of 9-10-10. Focal and generalized jerks were noticed soon after birth when loud noises occurred or when the infant was touched (particularly on the face or forehead). The jerks were asociateded with stiffness, slightly more pronounced in the lower limbs. During sleep, muscle tone was normal. In the first months, massive jerks occurred only during quiet sleep in response to sudden tactile or sound stimulations. Familial history disclosed massive jerks after unexpected stimuli, e.g., touching the tip of the nose or tapping the shoulder, in both the father and paternal grandfather.

At age 1 month, complete blood cell count, urinalysis, blood electrolytes, glucose, calcium, phosphorus, creatinine, uric acid, SGOT, SGPT, lactic dehydrogenase, alkaline, phosphatase, bilirubin. total protein, albumin, cholesterol, and triglyceride levels were normal. Metabolic screening for urinary amino acids was negative. Echoencephalogram, nuclear magnetic resonance imaging, and sleep and waking EEGs were normal. Polygraph recordings of paroxysmal episodes showed generalized rhythmic myoclonias (10-12/s) after stimulation, and the EEG showed diffuse low-voltage myogenic fast activity with slowing of background biorhythms at the end of seizures, probably caused by alterations in cardiorespiratory rate (Fig. 1). Seizures occurred while the patient was asleep and lasted from 20 s to several minutes. Seizures were partially reduced by treatment with oral clonazepam. The parents had discovered that longer seizures could be stopped promptly by flexing the infants head and legs toward the trunk. This method was always effective. Seizures continued to occur daily until the baby was aged 4 months. Stiffness gradually decreased, although some paratonus was still evident at 18 months. The infant began kinesitherapy dt 4 months. Growth and development were normal and at 1 year he was walking without support and saying a few words. At age 3 years, the child was completely normal: mild hypertonia of the (lower limbs was, noticeable when he became upset or irritated.

DISCUSSION

Our case is a major form of startle syndrome with neonatal onset (Andermann et al., 1980). In our patient, both longer seizures and simple startle reaction, were accompanied by a sharp electropositive EEG wave, bisynchronous over the parietooccipital regions. In stronger startle reactions, these tended to diffuse anteriorly with a latency of a few milliseconds. Spike-wave complexes, whose voltage depended on stimulus intensity. were probably arti[...] rather than cortical potentials, interpretable as evoked responses to the sensory stimulus (Gastaut and Villeneuve, 1967). This surface electropositive shart wave evidently is not ocular in origin (Markand et al., 1984) because it is either absent in prefrontal areas or appears first in the parietooccipital areas(Fig. 2).

Our case supports the familial occurence of startle disease (Suhren et al., I966; Andermann et al., l980). Startle seizures may be misdiagnosed if one is not aware of this syndrome. Medication effects arc variable (Kurczynski, 1983; Vigevano et al. 1989). The best treatmcnt for longer seizures, a potential cause of sudden infant death, is forcible flexion of the baby's. head and legs toward the trunk (Vigevano et al. 1989)

lt is of interest that in our case this method was devised spontaneously by the baby's parents. Long-term prognosis appears good for psychomvtvr development.

REFERENCES

Andermann F, Keene DL. Andermann E. Quesney LF. Startle disease or hyperekplexia: further delineation of the syndrome.Brain 1980:103:985-7.

Brown P, Rothwell JC, Thompson PD, Britton TC. Day BL, Marsden D. The hyperekplexias and their relationship to the normal startle reflex. Brain 1991;114:1903-28.

Dooley MJ. Andermann F. Startle disease or hyperekplexia....