How can you differentiate anterior interosseous nerve (AIN) syndrome from carpal tunnel syndrome?

The differentiation between anterior interosseous nerve (AIN) syndrome and carpal tunnel syndrome can be made by understanding the symptoms and functions affected by each condition.

In AIN syndrome, the anterior interosseous nerve, a branch of the median nerve, primarily affects motor function and does not typically present with sensory symptoms. Patients may experience weakness in the flexor pollicis longus, the flexor digitorum profundus to the index finger, and the pronator quadratus muscles, leading to difficulty with specific hand and finger movements, such as making a fist or pinching. However, because the sensory fibers of the median nerve remain intact, sensory symptoms are not present in AIN syndrome.

This contrasts with carpal tunnel syndrome, which arises from compression of the median nerve at the wrist. Carpal tunnel syndrome typically causes both sensory symptoms, such as numbness or tingling in the thumb, index, and middle fingers, as well as motor weakness, particularly in the thenar muscles and, in advanced cases, the lumbricals.

Therefore, identifying the absence of sensory symptoms in AIN syndrome as compared to the clear sensory involvement in carpal tunnel syndrome is crucial for making an accurate diagnosis.