Progressive muscular atrophy is marked by slow but progressive degeneration of only the lower motor neurons.
It largely affects men, with onset earlier than in other motoneurone diseases. Weakness is typically seen first in the hands and then spreads into the lower body, where it can be severe. Other symptoms may include muscle wasting, clumsy hand movements, fasciculations, and muscle cramps. The trunk muscles and respiration may become affected. Exposure to cold can worsen symptoms.
When the disease remains confined to the lower motor neuron, survival may be prolonged compared with classic amyotrophic lateral sclerosis (ALS). Most, however, develop upper motor neuron (UMN) signs later in their clinical course, at which point the disease is called “LMN-onset ALS”.