Subacute sclerosing panencephalitis

SSPE develops in roughly one in ten thousand to one in a hundred thousand measles cases, with much higher risk when infection occurs before two years of age, and typically appears seven to ten years later. The virus persists in neurons and glia in a defective form, most often lacking a functional M (matrix) protein, so infectious particles are not assembled and the virus spreads cell to cell, evading antibody. Clinically it evolves through stages: insidious behavioural and school-performance decline, then characteristic periodic myoclonic jerks with a burst-suppression pattern on EEG, then spasticity, rigidity, and akinetic mutism, and finally autonomic failure and death over one to three years. Diagnosis rests on markedly elevated anti-measles antibody titres in CSF with oligoclonal bands. There is no effective treatment; the only prevention is measles vaccination, and rising SSPE incidence tracks falling vaccination coverage.