SSPE is also known as Dawson Disease, Dawson encephalitis and measles encephalitis. It is a rare chronic, progressive encephalitis that affects primarily children and young adults, caused by a persistent infection of immune resistant measles virus (which can be a result of a mutation of the virus itself). No cure for SSPE exists, but the condition can be managed by medication if treatment is started at an early stage.

Characterized by a history of primary measles infection usually before the age of 2 years, followed by several asymptomatic years (6–15 on average), and then gradual, progressive psychoneurological deterioration, consisting of personality change, seizures, myoclonus, ataxia, photosensitivity, ocular abnormalities, spasticity, and coma. Death usually occurs within 3 years.