Late onset hyperekplexia.

We report on the case of an 86-year-old woman who rapidly became unable to stand and walk because of jerky movements, suggesting a clinical diagnosis of myoclonus. It was observed that both unexpected and expected stimuli (audiogenic, tactile, or visual) triggered the myoclonic jerks. Electrophysiological exploration, including a coupled EEG-EMG study, showed the occurrence of a patterned motor response to each stimulation (whatever the modality), consisting of eye blinking, head flexion, abduction of the upper arms, movement of the trunk, and bending of the knees. Given the absence of any relevant past history and lack of biological or neurological abnormalities including on CT scan brain imaging, the diagnosis of late-onset hyperekplexia was suggested. Substantial abatement of the clinical symptomatology was obtained after introduction of low-dose clonazepam.