In ALS, which statement best describes the pattern of UMN and LMN involvement over the course of the disease?

• A. UMN involvement in large muscles declines; LMN in a single muscle group becomes dominant in late stage
• B. UMN signs dominate throughout with no LMN signs
• C. LMN signs precede UMN signs in all cases
• D. UMN and LMN signs appear only in early stages

Answer: (A)

ALS affects both upper and lower motor neurons, so you see a mix of UMN signs (like spasticity and brisk reflexes) and LMN signs (such as weakness with atrophy and fasciculations) from the disease’s course. As it progresses, the LMN component often becomes more clinically prominent, especially in the larger proximal muscles, and weakness with muscle wasting spreads to more muscle groups. This reflects a shift toward LMN-predominant weakness in the later stages, which is why the description that UMN involvement in large muscles wanes while LMN involvement in a muscle group becomes dominant late in the disease best fits the overall pattern. The other statements don’t match the typical course because UMN and LMN signs coexist throughout, LMN signs don’t reliably precede UMN signs in all cases, and signs aren’t confined to early stages.