The
progressive myoclonus epilepsies (PMEs) are a devastating group of rare disorders(1) that manifest with increasing
action myoclonus, which is also present at rest but activates with stimuli such as noise, light, or touch. Ultimately, patients become wheelchair-bound and experience early death.
Neurologic signs that frequently but not reliably coexist include other seizure types (particularly generalized tonic-clonic), progressive
ataxia, and
dementia. Typically, presentation is in late childhood or adolescence; however, all ages may be affected. Although distinction from more common forms of genetic
generalized epilepsy, particularly
juvenile myoclonic epilepsy, may be challenging early on, the presence or evolution of 1) progressive neurologic disability, 2) failure to respond to
antiepileptic drug therapy, and 3) background slowing on EEG should suggest PME. Importantly, inappropriate
therapy in the genetic
generalized epilepsies may result in
ataxia, impaired cognition, and uncontrolled
seizures, which may mimic PME. PMEs should be distinguished from progressive
encephalopathies with
seizures (due to degenerative conditions such as
GM2 gangliosidosis,
nonketotic hyperglycinemia, Niemann-Pick type C, juvenile Huntington and
Alzheimer disease) and progressive myoclonic
ataxias, which affect predominantly adults with progressive
ataxia,
myoclonus, few if any
tonic-clonic seizures, and without evidence of
dementia.(2,3.)