Résumé
The aim of this work is to study the cognition, progressive gait impairment, and neuroimaging findings in two patients over 65 years old of the previously described type 3 familial cortical myoclonic tremor with epilepsy (FCMTE3). We report investigations in two of these five FCMTE3 subjects over 65 and showing progressive gait disorders. They both had a pseudo-Parkinson's way of walking and visual intolerance to bright light and brightness contrast without EEG abnormalities exacerbating cortical myoclonus or triggering seizure. Case 1 had moderate gait impairment and a severe frontal syndrome. Case 2 had severe gait impairment and diffuse cognitive disorders. Both cases had cortical hypoperfusion (predominantly in the left frontal lobe) and no cerebellar abnormality on cerebral perfusion SPECT. DAT-SPECT showed dopaminergic depletion. These data indicate fronto-striatal dysfunction associated with gait impairment and cognitive disorders appearing after several decades of disease progression. This gives clues to understanding the pathogenesis and evolution of FCMTE3. Permanent myoclonic discharges or long-term valproate treatment may cause significant toxic effects on neurons (dopaminergic and frontal neurons). Further functional and molecular analyses are required in order to better understand this pathology and the consequences of chronic cortical myoclonus.