Carpal tunnel syndrome
Carpal tunnel syndrome is the most common median nerve entrapment syndrome. It is caused by median nerve entrapment by the transverse carpal ligament at the wrist. Women are 4 times more likely to be affected as men. Most cases are occupation-related, caused by repetitive hand movements. Other causes include systemic illnesses such as rheumatoid arthritis, hypothyroidism, systemic lupus erythematosus, multiple myeloma, and diabetes mellitus, as well as obesity and pregnancy.
Patients present complaining of painful numbness and tingling in the first three digits (thumb, index finger, and middle finger), especially at night while asleep or with wrist flexion. Grip weakness may also be present.The Phalen’s maneuver and Tinel’s sign are physical exam maneuvers that evoke pain in the median nerve distribution, although not perfectly sensitive and thus not necessary for diagnosis. Diagnosis is made on the basis of a complete history and physical exam and can be confirmed by nerve conduction studies.
Treatment is initially managed conservatively, including rest, wearing a wrist splint at night, and with oral pain medications such as NSAIDs. Steroid injection may also be attempted. Most cases improve non-surgically. In those that do not, carpal tunnel release is a common surgical procedure that provides relief in over 70% of patients.
Pronator Teres Syndrome
Pronator Teres Syndrome is a rare cause of median nerve entrapment, in which the median nerve is compressed at the elbow by the two heads of the pronator teres muscle. Symptoms can be similar to carpal tunnel syndrome, including paresthesias in the thumb and index finger and grip weakness. However, distinguishing features include pain and numbness in the palm and easy fatiguing of forearm muscles. Repeated pronation exacerbates symptoms. On exam, palpation over the proximal median nerve elicits tenderness, while resisted pronation evokes symptoms. Rest, massage therapy, and corticosteroid injection can alleviate pain. The vast majority of cases resolve on their own. Surgical decompression may be considered in select cases that do not respond to conservative management.
Anterior interosseous nerve syndrome
This syndrome is another rare median nerve neuropathy. The anterior interosseous nerve is a motor branch of the median nerve. Trauma is the most common cause, including supracondylar fracture, open reduction of a forearm fracture, elbow dislocation, or penetrating injury such as a stab wound. Three muscles are affected: the flexor digitorumprofundus, flexor pollucislongus, and pronator quadratus. Patients complain of forearm pain and weakness making a pincer using the thumb and index finger. Importantly, there is no sensory deficit. Electromyography (EMG) may be used in addition to physical exam findings for diagnosis. Non-surgical management should first be attempted for 8-12 weeks. If unsuccessful, surgical decompression is highly effective as definitive treatment.
References
- Greenberg M. Handbook of Neurosurgery. 6th ed. New York: Thieme Medical Publishers, 2005.