Photosensitivity in Lafora and Unverricht-Lundborg progressive myoclonic epilepsies

Lafora disease (LD) and Unverricht-Lundborg disease (EPM1A) are the most common forms of progressive myoclonic epilepsy and are frequently associated with photosensitivity and photic reflex myoclonus (PRM). This study aimed to characterize the photoparoxysmal response (PPR), evaluate the effect of blue lenses, and explore the neural networks underlying PPR and PRM in both conditions.

Twenty-six patients with LD and 51 with EPM1A were included. PPR was assessed on the first available electroencephalogram (EEG), including background activity and the presence and distribution of interictal epileptiform discharges, which were compared between groups. A subset of patients underwent back-averaging analysis using 1-Hz flash stimuli as triggers, allowing identification of the principal components of flash-evoked responses.

PPR was detected in 85% of LD patients and 33% of EPM1A patients (p < .001). Compared with EPM1A, LD patients more often showed focal seizures with visual symptoms, slower EEG background activity, and a higher presence of focal epileptiform abnormalities over the posterior regions. In both groups, PPR was mainly Waltz type 4 at 14-15 Hz and was associated with PRM in approximately half of the cases. However, in LD, the PPR latency from stimulus onset was shorter, and sensitivity to blue lenses was significantly lower. Compared with healthy controls, both patient groups exhibited increased amplitude and prolonged latency of the flash-evoked responses.

Photosensitivity is more frequent and severe in LD than in EPM1A and is associated with electrophysiological markers of occipital cortex hyperexcitability. The shorter PPR latency in LD suggests an intrinsic predisposition to generate PPR immediately after visual input, possibly related to a lack of inhibitory mechanisms. The frequent occurrence of PRM in both conditions reflects aberrant large-scale network dynamics involving cortical and subcortical structures rather than pure occipital cortex dysfunction.