Hypsarrhythmia in a child is due to –
Myoclonic epilepsy may be

Infantile spasm or Infantile myoclonus or West syndrome
Juvenile myoclonic epilepsy

Infantile spasm (Infantile myoclonus or West syndrome) 

The onset is usually between 3-8 months of life
It is characterized by a triad of -

i) Salaam spells (sudden dropping of the head & flexion of arms)
ii) Mental retardation
iii) The hypsarrhythmic pattern of EEG (diffuse high voltage slow spike and chaotic activity)

The spasm occurs in clusters usually on waking.
Prognosis for normal mental development is poor.

Treatment of infantile myoclonus

ACTH and corticosteroids are given for 2-12 weeks, depending upon response.
Vigabatrin is the DOC Now.
Grandmal epilepsy
Petitmal epilepsy
Myoclonic epilepsy
Reflex epilepsy