Ataxia, apraxia, agnosia and Balints Syndrome may be seen. The myoclonic jerks initially, involve the head and subsequently spread to the trunk and limbs. There is a sudden flexion movement followed by a one to two second relaxation period. Initially they are infrequent, but as the disease advances, the myoclonus occurs every 5 to 15 seconds with further progression, extra pyramidal disorders occur. There is an expressionless face, paucity of spontaneous movement and appearance of dystonic movements.
Decelerate rigidity becomes manifest in the final phase of the illness.
Chorioretinitis, cortical blindness and abnormal eye movements may occur in some patients. Terminally death results from aspiration pneumonia or irreversible autonomic abnormalities. Pathogenesis Natural infection with measles can take several courses, however the pathogenesis of SSPE remains unclear. It has been hypothesized that lack of M protein results in intracellular accumulation of incomplete measles virions in brain cells. The host immune response is unable to clear the intracellular infection and the persisting accumulation leads to neuronal dysfunction.