Does primary lateral sclerosis exist? A study of 20 patients and a review of the literature

The question of whether primary lateral sclerosis (PLS) is a nosological entity distinct from amyotrophic lateral sclerosis (ALS) has been the subject of controversy since it was first described in the nineteenth century. PLS has been defined as a rare, non-hereditary disease characterized by progressive spinobulbar spasticity, related to the selective loss of precentral pyramidal neurones, with secondary pyramidal tract degeneration and preservation of anterior horn motor neurones. In the recent clinical literature, the frontier between ALS and neurodegenerative disease remains poorly defined. We studied 20 patients with a diagnosis of PLS. We carried out a variety of tests in order to determine the presence of a more diffuse neurodegenerative process. We also performed a longitudinal electrophysiological evaluation. Our clinical, electrophysiological. and pathological investigations provide evidence that the disease has a heterogeneous clinical presentation and that degeneration is not restricted to the central motor system.