What is primary lateral sclerosis?

Primary lateral sclerosis (PLS) is a rare degenerative disorder of the uppe r motor neuron. Its nosological status and relationship to other motor neur on syndromes, especially amyotrophic lateral sclerosis (ALS), is uncertain. Diagnostic criteria have been proposed. We discuss the history of this rar e clinical disorder, its relationship to the motor neuron disease syndrome, and reports of overlapping clinicopathological conditions. Two patients wi th the clinical syndrome of PLS are described to illustrate current underst anding of the clinical, laboratory, and neurophysiological features. (C) 19 99 Elsevier Science B.V. All rights reserved.