Which statement best distinguishes pronator teres syndrome from anterior interosseous nerve entrapment?

• A. Pronator teres syndrome presents with sensory disturbances; anterior interosseous nerve entrapment is motor-only.
• B. Pronator teres syndrome is motor-only; anterior interosseous nerve entrapment presents with sensory disturbances.
• C. Both conditions have sensory disturbances.
• D. Both conditions are motor-only.

Answer: (A)

The key distinction is which nerve fibers are affected. Pronator teres syndrome compresses the median nerve at the elbow and can involve both motor and sensory fibers, so patients often have sensory disturbances in the median nerve distribution of the hand along with motor weakness of median-nerve–innervated forearm muscles. Anterior interosseous nerve entrapment is a lesion of the anterior interosseous nerve, a motor branch of the median nerve, leading to weakness of deep forearm flexors (such as FPL and parts of FDP) without any sensory loss. So sensory symptoms point to pronator teres syndrome, while pure motor weakness with preserved sensation points to anterior interosseous nerve entrapment. Clinically, anterior interosseous nerve entrapment can produce a specific pinch- or OK-sign deficit due to impaired FPL and FDP function, with normal sensation.