The Benign Course of PLS

Primary lateral sclerosis (PLS) is a rare, slowly progressive, neurodegenerative disorder in adults characterized by an isolated degeneration of the upper motor neurons (UMN) in the absence of lower motor neuron (LMN) signs.1,2 PLS constitutes about 2%–5% of patients seen in adult neuromuscular clinics. This condition is characterized by slower progression, prolonged retention of functionality, sparing of ventilation muscles, and longer survival compared to classical amyotrophic lateral sclerosis (ALS). Therefore, the distinction between PLS and ALS, especially soon after symptom onset, requires care and scrupulous evaluation.