Startle disorders of man: hyperekplexia, jumping and startle epilepsy.

Startle is a basic alerting reaction common to all mammals. A rapid reflex not amenable to voluntary control, it was studied extensively by Strauss in 1929 [1], and is the subject of a monograph by Landis and Hunt [2] and a more recent study by Gogan [3]. In the human adult, except for minor interpersonal variations, a stereotyped motor pattern is seen consisting of eye blinking facial grimacing, flexion of the head, elevation of the shoulders, and flexion of the elbows, trunk and knees. With repeated stimulation, the intensity of the surprise reaction decreases, but never completely disappears. Tension, fatigue and heightened expectation of the stimulus enhance it. The intensity is greater in infancy where it appears at the same time as the Moro reflex (an extensor response to sudden stimuli). However, startle becomes more noticeable in time, while the Moro reflex disappears [4] . This reflex, so basic to man, can be present in a pathologically exaggerated form which is always embarrassing, sometimes interferes with normal activities, and occasionally may be dangerous. The pathophysiology of startle was recently reviewed by Wilkins et al [5] . Abnormal, excessive startle is a feature of three distinct conditions: startle disease or hyperekplexia,jumping (the jumping Frenchmen of Maine) and startle epilepsy (Table 1).