Pronator syndrome and anterior interosseous nerve syndrome.

Dysfunction of the median nerve at the elbow or proximal forearm can characterize two distinct clinical entities: pronator syndrome (PS) or anterior interosseous nerve (AIN) syndrome. PS is characterized by vague volar forearm pain, with median nerve paresthesias and minimal motor findings. AIN syndrome is a pure motor palsy of any or all of the muscles innervated by that nerve: the flexor pollicis longus, the flexor digitorum profundus of the index and middle fingers, and the pronator quadratus. The sites of anatomic compression are essentially the same for both disorders. Typically, the findings of electrodiagnostic studies are normal in patients with PS and abnormal in those with AIN syndrome. PS is a controversial diagnosis and is typically treated nonsurgically. AIN syndrome is increasingly thought to be neuritis and it often resolves spontaneously following prolonged observation. Surgical indications for nerve decompression include persistent symptoms for >6 months in patients with PS or for a minimum of 12 months with no signs of motor improvement in those with AIN syndrome.