Carpal tunnel syndrome is caused by elevated pressure in the carpal tunnel which is located at the base of the palm, just beyond the wrist crease extending into the hand. The tunnel is formed on three sides by the wrist bones, which create an arch, and on the palm side by a large ligament called the transverse carpal ligament. Nine flexor tendons (two extending to each finger and one to the thumb) traverse the carpal tunnel, along with the median nerve. This increased pressure produces a lack of blood supply to the median nerve, resulting in impaired nerve function (electrical conduction) and attendant numbness, tingling and pain. Early in the course, no morphologic changes are observable in the median nerve, neurologic findings are reversible, and symptoms are intermittent. Prolonged or frequent episodes of elevated pressure in the carpal tunnel may result in more constant and severe symptoms, occasionally with weakness. When there is prolonged ischemia or lack of blood supply, axonal injury ensues, and permanent nerve damage may occur.
A variety of conditions may be associated with carpal tunnel syndrome. These include pregnancy, inflammatory arthritis, Colles' fracture, amyloidosis, hypothyroidism, diabetes mellitus, acromegaly and use of corticosteroids and estrogens. Up to one third of cases of carpal tunnel syndrome occur in association with such medical conditions; about 6% of patients have diabetes. Carpal tunnel syndrome is also associated with repetitive activities of the hand and wrist, particularly with a combination of forceful and repetitive activities. Occupations associated with a high incidence of carpal tunnel syndrome include food processing, manufacturing, logging, construction work and repetitive tasks such as typing.
A combination of electrodiagnostic studies (nerve-conduction studies and electromyography) and knowledge of the location and type of symptoms permits the most accurate diagnosis of carpal tunnel syndrome. Symptoms consistent with carpal tunnel syndrome occur in up to 15% of the population. Both symptoms and electrodiagnostic studies must be interpreted carefully. Electrodiagnostic studies are most useful for confirming the diagnosis in suspected cases and ruling out neuropathy and other nerve entrapments.
Loss of two-point discrimination in the median-nerve distribution (inability to distinguish between one sharp point on the fingertip and two) as well as thenar atrophy (flattening of the palm muscle near the thumb) occur late in the course of carpal tunnel syndrome. Several provocative tests may assist in the diagnosis. In Phalen's maneuver, the patient reports whether flexion of the wrist for 60 seconds elicits pain or paresthesia in the median-nerve distribution. Tinel's sign is judged to be present if tapping lightly over the surface of the wrist causes radiating paresthesia in the digits innervated by the median nerve. The sensitivity of Tinel's sign ranges from 25% to 60%. In the pressure provocation test, the examiner's thumb is pressed over the carpal tunnel for 30 seconds. In the tourniquet test, a blood pressure cuff is inflated around the arm to above systolic pressure for 60 seconds. Both tests are deemed positive if they elicit radiating paresthesia in the median nerve distribution. Since findings on physical examination and the history have limited diagnostic value, they are most useful when there is a reasonable clinical suspicion of carpal tunnel syndrome (as when a patient presents with hand symptoms).
When carpal tunnel syndrome arises from rheumatoid arthritis or other types of inflammatory arthritis, treatment of the underlying condition generally relieves carpal tunnel symptoms. Treatment of other associated conditions (such as hypothyroidism or diabetes mellitus) is also appropriate, although data are lacking on whether such treatment alleviates carpal tunnel syndrome. Similarly, it is not known whether stopping medications associated with carpal tunnel syndrome (such as corticosteroids or estrogen) leads to improvement, although taking such a step is also reasonable in the absence of contraindications.
More than 80% of patients with carpal tunnel syndrome report that a wrist splint alleviates symptoms, generally within days. Splints are more effective if they maintain the wrist in neutral posture rather than in extension. Commercially available splints are acceptable, provided that they maintain such a neutral position.
Nonsteroidal antiinflammatory medications, diuretics and pyridoxine (vitamin B6) have each been studied in small, randomized trials but do not appear to be effective. Oral steroid medications such as prednisolone do show at least short-term improvement and may be tried if there are no medical contraindications. The use of corticosteroids have some risk including weight gain, hypertension and hyperglycemia even with short-term treatment.
Local Corticosteroid Injection
Patients who remain symptomatic after modification of their activities and splinting are candidates for injection of corticosteroids into the carpal tunnel. Injection of corticosteroids improves symptoms in more than 75% of patients. Local injection of corticosteroids is also associated with improvement in median nerve electrical conduction. Symptoms generally recur within one year. Risk factors for recurrence include severe abnormalities on electrodiagnostic testing, constant numbness, impaired sensibility and weakness or thenar muscular atrophy. The risks of infection and nerve damage resulting from corticosteroid injection are considered to be low. Many clinicians limit the number of injections into the carpal tunnel (as they would for other sites) to about three per year in order to minimize local complications (such as rupture of tendons and irritation of the nerves) and the possibility of systemic toxic effects (such as hyperglycemia or hypertension). In general, conservative treatment is more successful in patients with mild nerve impairment. In one study, 89% of patients with severe carpal tunnel syndrome (constant numbness with weakness, atrophy or sensory loss) had recurrence of the syndrome within one year after a conservative program that included splinting and injection of corticosteroids into the carpal tunnel. Among patients with mild carpal tunnel syndrome (intermittent numbness and normal sensory and motor findings on physical examination), 60% had recurrence of symptoms after such conservative treatment.
In general, the decision about whether to proceed with carpal tunnel–release surgery should be driven by the preference of the patient. However, if a patient has symptoms and signs that are suggestive of nerve damage — constant numbness, symptoms for more than one year, loss of sensibility and thenar muscular atrophy or weakness — surgery should be seriously considered.
We perform a mini-open release that uses an incision of 2.0 to 2.5 cm to release the transverse carpal ligament under direct visualization. This approach is used in an attempt to achieve earlier recovery while avoiding the complications that have been associated with endoscopic approaches including symptom recurrence. The laser does not have an application in carpal tunnel syndrome surgical treatment.
More than 70% of patients report being completely satisfied or very satisfied with the results of carpal-tunnel surgery. Similarly, 70% to 90% of subjects report being free of nocturnal pain after surgery. After surgery, pain relief occurs within days, but hand strength may not reach preoperative levels for several months. Tenderness of the surgical scar may also persist for some time. Patients with better general functional status and mental health have more favorable outcomes after carpal tunnel release.
Acupuncture for carpal tunnel syndrome has not been evaluated in controlled studies. In a randomized trial, an intervention involving yoga-based stretching, strengthening, and relaxation in patients with carpal tunnel syndrome resulted in greater improvement in grip strength and reduction of pain than did splinting.
Patients with discomfort of the hand and wrist should be evaluated with a detailed history of symptoms (which can be facilitated with a diagram of hand pain) and a physical examination that includes tests of sensory and motor nerve function and provocative maneuvers. If carpal tunnel syndrome seems likely, conservative management with splinting should be initiated. If splinting causes discomfort during the performance of some hand-intensive tasks, it is advisable either to avoid the activity or to perform it without the splint. We suggest that patients reduce activities at home and work that exacerbate symptoms. Although the effects of nonsteroidal antiinflammatory medications on carpal tunnel syndrome have not been well studied, we generally suggest a trial of these agents if there are no contraindications. We do not recommend use of vitamin B6 (because there is no evidence of efficacy). Oral corticosteroids may be used as long as the patient understands the possibility of short-term side effects. If the condition fails to improve, we recommend corticosteroid injection into the carpal tunnel region and/or surgical intervention to decompress the nerve in an open, minimally invasive approach.