Clinical and electrophysiological pattern of startle epilepsy: a comprehensive literature review

Abstract

Startle epilepsy is a rare form of epilepsy characterized by recurrent seizures that are triggered by a surprising stimulus. It affects children between 10 months and 14 years of age, with a history of brain damage due to ante- or neonatal hypoxia, and hemiparesis. The most common triggers for these seizures are auditory stimulation, followed by somesthetic stimulation and visual stimulation. Typical startle seizures are rare, and they have a large variety of clinical manifestations. The most frequent type is short hemitonic flexion seizures, followed by myoclonic seizures, and bilateral tonic seizures. Few studies have focused on the electrophysiological features of this condition and the literature is controversial regarding the EEG pattern. Interictal EEG is often normal. The most frequent interictal abnormalities are a slowing of the background rhythm, associated with focal spikes in the frontal, central, and parietal regions. Several ictal EEG patterns have been reported: diffuse flattening of the background rhythm, focal fast activity, an isolated focal spike followed by a discharge of spikes. Intracerebral EEG recording shows primary and secondary motor cortex involvement as initial discharge areas. The most efficient antiepileptic drugs are Lamotrigine, Oxcarbazepine, and benzodiazepines. But most patients are often drug-resistant. Surgery is a possible albeit rare therapeutic option. We describe the case of a 13-year-old female patient with hemitonic seizures triggered by surprising auditory stimuli. The video EEG allowed us to record and define an EEG pattern of her seizures. Interictal EEG showed right fronto-central abundant spikes. The ictal EEG showed right fronto-central and medial spikes followed by a fronto-central fast rhythm discharge. The clinical and electrographic data permitted the diagnosis of startle epilepsy. Our patient was treated with Levetiracetam during 6 months followed by Oxcarbazepine and Clobazam with a partial improvement (reduction of the frequency of focal to bilateral tonic-clonic seizures). Considering the usual pharmaco-resistance of this type of epilepsy, we proposed our patient a presurgical evaluation. This case shows that the diagnosis should be considered in paroxysmal dystonic movements with a stereotyped triggering factor, and underlines the importance of repeating the EEG recordings in this type of epilepsy. In this article we will review the literature, discuss the underlying pathophysiology, and identify the common electrophysiological characteristics associated with startle epilepsy.