What are the radiological and clinical features of subacute sclerosing panencephalitis (SSPE), and how is it related to measles infection?

Subacute sclerosing panencephalitis (SSPE) is a progressive, fatal neurodegenerative disorder caused by a persistent infection with a mutated measles virus. It typically occurs in children and young adults who had measles before age 2, manifesting after a 6- to 10-year asymptomatic period. Clinically, it presents with progressive dementia, myoclonus, seizures, and paralysis. Radiologically, early findings include focal lesions in the gray matter and subcortical white matter, with later stages showing periventricular white matter lesions that may enhance and profound cortical atrophy. Key diagnostic features include elevated measles antibody titers in the cerebrospinal fluid. A common pitfall is mistaking SSPE for other causes of progressive neurological decline, such as multiple sclerosis or other viral encephalitides.