Figure 3. Characteristics distinguishing patients with undetermined progressive myoclonic epilepsies.

Cluster 1 included more patients in whom psychomotor (PM) delay preceded the appearance of cortical myoclonus, EEG paroxysms evoked by intermittent photic stimulation, and atrophic changes in the cerebral cortex or cerebellum, whereas cluster 2 included a larger number of patients with associated signs exceeding the typical progressive myoclonic epilepsies presentation (A). Recurrent and polymorphic seizures were more common in cluster 1 (B), whereas almost half of the patients in cluster 2 had no seizures (other than myoclonic) (C). Sz = seizures; TC = tonic-clonic.