Startle response: epileptic or non-epileptic? The case for "flash" SMA reflex seizures

A 19-year-old woman complained of long-standing, frequent, debilitating brusque movements triggered by unexpected stimuli. She was neurologically normal and neuroimaging was also normal. Conspicuous startle reactions were easily reproduced under EEG and video monitoring: the interictal EEG was normal, the ictal recordings doubtful; clinically, the startle reaction was asymmetric, with elevation of the left limbs. The diagnosis of hyperekplexia and startle epilepsy were discussed. We learned that she had been evaluated at age 3-4 months for spontaneous, generalised tonic-clonic seizures and "infantile spasms", in fact for early-onset startle reactions triggered by noise or contact, in association with prominent EEG changes. A full remission had been achieved under ACTH therapy, but the startle reactions had reappeared at around age six. The patient was successfully treated with carbamazepine. The history, clinical and neurophysiological data led us to discuss the diagnosis of hyperekplexia and startle epilepsy. We concluded that the patient had an unusual form of cryptogenic focal epilepsy originating from the supplementary motor area, presenting as strictly stimulus-triggered "flash" seizures.