Juvenile Huntington's disease masquerading as progressive myoclonus epilepsy

Juvenile Huntington's disease (JHD) has an onset before 20 years of age, and is characterized by behavioural issues, epilepsy, rigidity, bradykinesia and dystonia. It contributes to 0.5-5% of all Huntington disease (HD) cases. JHD demonstrates a more rapid progression and is characterised by dystonia, as opposed to the slow progression with predominant chorea seen in adult-onset HD. Seizures are described in 38% of JHD as compared to 2% in the adult onset HD. The different types of seizures reported in JHD are generalized seizures, myoclonus, absence seizures and less commonly tonic and focal seizures with impaired awareness. JHD patients have good seizure control initially and develop drug-resistant epilepsy in the later stages of the disease which is rarely reported. Here, we report the case of a 13 -year-old boy, who initially presented with generalized tonic-clonic seizures followed by myoclonic jerks, with subsequent cognitive decline, ataxia, involuntary movements and drug resistant epilepsy mimicking a progressive myoclonus sepilepsy. His EEG changed from normal background with generalized interictal epileptiform discharges to diffuse slowing with fast activity devoid of epileptiform activity to reflect electroclinical evolution of the disease process.