Trigeminally induced startle in children with hyperekplexia.

To determine the physiological features of startle reactions in children with hereditary hyperekplexia, motor responses to auditory and trigeminal stimulation were investigated in 2 patients and 3 control subjects by means of multiple surface electromyographic recordings. The pattern of motor activation in auditory startle was similar in the two groups, although the responses in the patients were increased in terms of the extent of the responses. In the patients, nose taps elicited two separate responses in various muscles. The initial, short-latency response was often elicited in all the muscles examined. This reflex was similar to the R1 component of the electrical blink reflex. In addition, the early reflex was immediately followed by the second response, which also appeared widely and was similar to R2 of the blink reflex. Taps on the supraorbital nerve elicited multiple startle patterns consisting of these two responses, although generalization was infrequent. In the control subjects, these responses were elicited in a few muscles. In the hyperekplectic children, both the early and second responses to trigeminal stimulation were increased, in addition to the audiogenic reflex. It was suggested that enhancement of these responses occurred due to hyperexcitability in the brainstem reticular formation in our patients. Copyright 2004 Movement Disorder Society.