Abstracts

Rationale: Scotosensitivity is characterized by emergence of occipital spike and slow waves upon eye closure, or darkness and abates in response to eye opening in light room as well as fixation in dark. It has been classically described in early and late onset occipital lobe epilepsies. The scotosenstive occipital spikes are also reported to precede scotosensitve myoclonus occurring in the context of mitochondrial disease. The myoclonus is thought to represent the spread of this epileptiform activity from the occipital cortex to areas involving generation of motor movements. Here we present a case of scotosensitive ictal myoclonus with no occipital spikes in the EEG. Methods: 22-year old right-handed male with no known cognitive deficits had his first generalized tonic clonic seizure at 17 years of age. His epilepsy became refractory to medication in the following 3-5 year and during periods of seizure exacerbation he had apparent cognitive decline. Family history was negative for epilepsy, myoclonus or neurodegeneration. Brain MRI showed no structural abnormalities and normal anatomy. Somatosensory evoked potentials were not enhanced. Genetic testing was deferred due to economical reasons. Video EEG monitoring was done with XLTEK video-electroencephalograph system and application of standard 10-20 electrodes. Results: Clinically during the video EEG he had spontaneous myoclonus involving different cranial, axial and appendicular muscle at different times during wakefulness. Upon discontinuation of antiepileptic medication he was noted to develop eyelid, neck and appendicular myoclonia (including gluteal muscles). There was an increase in frequency of his myoclonic jerks as well as further alteration of consciousness prior to generalization. After resumption of antiepileptic medication he started to have axial myoclonus affecting abdominal and diaphragmatic muscles, causing hiccups for several days. Scotosensitivity was clinically demonstrated: upon eye closure or switching off the lights he had eye globe myoclonus, followed by neck and axial myoclonus affecting upper torso and shoulders. His EEG only showed high amplitude 2-4 Hz semirhythmic delta slowing during scotosensitive and spontaneous myoclonia. At no times he had spike bursts or sharp waves during or preceding his myoclonic events. There were no occipital spikes in response to darkness or photic stimulation. Conclusions: There is no neurophysiological evidence of local cortical epileptic hyperexcitability preceding our patient s spontaneous or reflex myoclonus (i.e. there are no occipital spikes, pre-myoclonic spike bursts, interictal epileptiform discharges or enhanced evoked potentials). The myoclonus is precipitated by darkness pointing to involvement of widespread cortico-cortical (possibly occipito-frontal) connections as well as an imbalance of inhibitory and excitatory mechanisms. The subsequent development of a generalized seizure points to eventual epileptic network perturbations. Therefore we conclude that a disinhibitory network phenomenon may be the basis of our patient s motor myoclonus well prior to epileptic affection of cortical reflex loop.