Fifteen patients with
hyperekplexia were identified in 3 families; diagnostic clinical characteristics were defined which allowed for early recognition and treatment. During the first 24 hours of life, spontaneous
apnea and sluggish feeding effort were observed. After the first 24 hours, surviving infants exhibited the hyperekplexic startle response to nose tapping. This startle response is characterized by sudden
muscular rigidity, feeding-induced oropharyngeal
incoordination, and poor air exchange often with
apnea, persisting with repetitive nose tapping. Untreated infants experienced recurring
apnea until 1 year of age. Three of 15 patients died unexpectedly during the neonatal period. Patients treated with
clonazepam (0.1-0.2 mg/kg/day) had no serious apneic episodes and startle reflexes were diminished. The pathophysiologic mechanism for
hyperekplexia remains obscure. Electroencephalographic studies were consistently normal. The response to and tolerance of
benzodiazepines are striking in newborns and infants and suggest an aberrant central nervous system reflex as the etiology; therefore,
hyperekplexia should be considered in the evaluation of neonates and infants with
apnea,
aspiration pneumonia, episodic
muscular rigidity, hyperexcitability, and near-miss
sudden infant death syndrome. The need for immediate monitoring of at-risk infants, observation for signs of
hyperekplexia, and initiation of
clonazepam in these patients are emphasized. Hyperekplexic startle response to nose tapping should be included in the routine examination of all newborns.