Primary lateral sclerosis; a debated entity.

Two patients suffering from slowly progressing spastic paraparesis are presented. Both of them underwent a several years' follow-up, and extensive laboratory, radiological and neurophysiological investigations in order to rule out known specific causes for pyramidal tract involvement. After these exclusion studies, the diagnosis of primary lateral sclerosis (PLS) was derived. The present cases provide further evidence of the long-debated PLS as a disease entity.