Which statement best describes amyotrophic lateral sclerosis?

• A. Involvement of both upper and lower motor neurons
• B. Sensory deficits predominate
• C. Only upper motor neuron signs
• D. Only lower motor neuron signs

Answer: (D)

Amyotrophic lateral sclerosis Characteristically shows degeneration of both upper motor neurons (in the brain) and lower motor neurons (in the spinal cord and brainstem). This combination creates a mix of signs: upper motor neuron features such as spasticity, hyperreflexia, and a positive Babinski sign, along with lower motor neuron features like weakness, muscle atrophy, and fasciculations. Sensation is typically preserved, at least early on, so sensory deficits do not predominate. If a disorder showed only upper motor neuron signs, or only lower motor neuron signs, or prominent sensory loss, that would point to a different condition. The hallmark of ALS is the concurrent involvement of both UMN and LMN pathways.