Which finding is most characteristic of limb-onset ALS?

• A. Fasciculations in the weak limb
• B. Proprioceptive deficits in limbs
• C. Visual disturbances
• D. Hearing loss

Answer: (A)

Limb-onset ALS shows motor neuron loss that leads to focal weakness in a limb along with signs of lower motor neuron dysfunction. The most characteristic finding in the affected limb is fasciculations—involuntary muscle twitches—reflecting irritable, degenerating lower motor neurons and ongoing denervation-reinnervation in that region. Sensation is typically preserved early in ALS, so proprioceptive deficits are not expected in the limb, which helps distinguish ALS from conditions with sensory involvement. Visual disturbances and hearing loss are not features of motor neuron disease and don’t fit the pattern of ALS.