Which ALS variant is characterized by upper motor neuron involvement only and slower progression?

• A. Progressive muscular atrophy
• B. Bulbar onset ALS
• C. Pseudobulbar palsy
• D. Primary lateral sclerosis

Answer: (D)

Primary lateral sclerosis presents with upper motor neuron signs without significant lower motor neuron involvement, and it tends to progress more slowly than classic ALS. In this condition, you see spasticity, hyperreflexia, and positive Babinski signs as the corticospinal tracts degenerate, but muscle atrophy and fasciculations from LMN loss are minimal or appear much later. That combination—UMN-dominant presentation with a slower course—fits the description well. Progressive muscular atrophy, by contrast, is driven mainly by lower motor neuron loss and shows early muscle wasting and fasciculations. Bulbar onset ALS involves both UMN and LMN pathways, affecting bulbar muscles early, and pseudobulbar palsy refers to UMN-mediated bulbar signs without implying a slow, pure UMN disease course.