Juvenile familial amyotrophic lateral sclerosis: four cases with long survival.

Four cases are reported of juvenile familial amyotrophic lateral sclerosis (JFALS) with exceptionally long survival (mean=27 years), and consequent development of dementia. Subjects' mean age at onset was 15.7 years. Their clinical features and electrophysiological findings support the diagnosis. One subject's MRI scan showed severe atrophy to the cortex and brain stem; wallerian degeneration in the pyramidal pathway, as reported in other studies, could not be found. JFALS is characterized by the involvement of other neuronal systems not present in the adult form and by long survival after disease onset.