What are the typical signs of Anterior Interosseous Nerve (AIN) syndrome?

• A. Loss of sensation and weakness of FPL and FDP
• B. Severe pain in the thumb
• C. Swelling in the palm
• D. Inability to fully extend the wrist

Answer: (A)

The typical signs of Anterior Interosseous Nerve (AIN) syndrome primarily involve motor function, specifically affecting the muscles innervated by the AIN, which include the flexor pollicis longus (FPL) and the flexor digitorum profundus (FDP) for the index and middle fingers. The loss of sensation in this syndrome is not a prominent feature because the AIN does not carry sensory fibers; it mainly focuses on motor innervation.

In AIN syndrome, patients often present with weakness in the thumb and the index finger, leading to difficulty with specific tasks that require flexion of these digits, such as pinching or grasping. This aligns with the correct answer, highlighting the weakness in both the FPL and the FDP.

Other options, while they may suggest problems in hand or wrist function, do not accurately reflect the specific characteristics of AIN syndrome. Severe pain specifically localized in the thumb is not a typical sign of AIN syndrome, which is generally not characterized by pain as the primary symptom. Similarly, swelling in the palm would suggest other pathologies, and the inability to fully extend the wrist typically relates to issues affecting wrist extensors or conditions like radial nerve palsy, rather than the A