Which combination of features is most characteristic of limb-onset ALS in the affected limb?

• A. Dysarthria and dysphagia
• B. Sialorrhea
• C. Weakness in ankle, finger, proximal arm/leg weakness; atrophy esp. thumb; fasciculations/cramps in weak limb
• D. Tongue fasciculations/atrophy

Answer: (C)

Limb-onset ALS most strongly presents with lower motor neuron signs confined to the affected limb: focal weakness that can involve distal and proximal regions, prominent muscle wasting—often of intrinsic hand muscles such as the thumb—and fasciculations or cramps in the weak limb. This pattern reflects degeneration of LMN pathways in the limb itself, which is the hallmark of limb-dominant presentation.

Bulbar signs like dysarthria, dysphagia, sialorrhea, or tongue fasciculations indicate involvement of the bulbar region rather than the limb itself, and thus are not the characteristic early features of limb-onset ALS in the affected limb.