Which of the following is least likely to present as asymmetric weakness?

Which of the following is least likely to present as asymmetric weakness?

• A. The right shoulder
• B. One the right side of the face
• C. The right hand
• D. Both arms

Answer: (D)

Asymmetric weakness points to a focal problem in the motor system that impacts one side of the body. When a lesion affects the corticospinal tract or a single peripheral nerve or facial nerve on one side, you see weakness limited to that side—such as one arm, one face, or one leg. Weakness confined to the right shoulder, or the right side of the face, or the right hand all reflect this kind of unilateral, asymmetric deficit. Weakness involving both arms, however, suggests a nonfocal or bilateral process rather than a single focal lesion. It implies either a diffuse or central issue affecting both sides (or a lesion high enough to influence both hemispheres) rather than a localized one-side problem. Therefore, weakness in both arms is least likely to present as asymmetric weakness.

Asymmetric weakness points to a focal problem in the motor system that impacts one side of the body. When a lesion affects the corticospinal tract or a single peripheral nerve or facial nerve on one side, you see weakness limited to that side—such as one arm, one face, or one leg. Weakness confined to the right shoulder, or the right side of the face, or the right hand all reflect this kind of unilateral, asymmetric deficit.

Weakness involving both arms, however, suggests a nonfocal or bilateral process rather than a single focal lesion. It implies either a diffuse or central issue affecting both sides (or a lesion high enough to influence both hemispheres) rather than a localized one-side problem. Therefore, weakness in both arms is least likely to present as asymmetric weakness.