subacute scle·ros·ing panencephalitis 
(sklə-rōsĭng)
(sklə-rōsĭng)n.
An often fatal degenerative disease of the central nervous system occurring chiefly in young people, caused by slow infection with a measles virus and characterized by progressive loss of mental and motor functions ending in dementia and paralysis.
[sclerosing, from sclerose, to harden, back-formation from SCLEROSED.]