Carpal Tunnel Syndrome

Monique Burton, MD, Jonathan Drezner, MD

Carpal tunnel syndrome, a cluster of symptoms resulting from compression of the median nerve, is the most common peripheral entrapment neuropathy. This condition is a frequent source of hand pain, affecting about 3% of the population. Women are affected three times more often than men.¹ This article reviews the pathoanatomy, diagnosis, and management of carpal tunnel syndrome for the primary care provider.

Anatomy
To evaluate a patient for carpal tunnel syndrome, it is helpful for the clinician to understand the relevant anatomy. The carpal tunnel is formed by the transverse carpal ligament (flexor retinaculum) ventrally and the carpal bones dorsally. Contained within the carpal tunnel are the median nerve and tendons of the flexor digitorum superficialis, the flexor digitorum profundus, and the flexor pollicis longus.

The median nerve divides within the tunnel to provide sensory distribution to the palmar aspect of the thumb, the index and middle fingers, and the radial half of the ring finger; and motor innervation to the abductor pollicis brevis, opponens pollicis, flexor pollicis brevis, and first and second lumbrical muscles. The palmar sensory cutaneous branch of the median nerve arises proximal to the carpal tunnel and supplies sensory innervation over the thenar eminence, thereby typically sparing this area from the potential effects of carpal tunnel syndrome.

Etiology
Carpal tunnel syndrome is typically a chronic condition, developing over months to years. The most common etiology is nonspecific flexor tenosynovitis that leads to swelling within the carpal tunnel and compression of the median nerve.²

Carpal tunnel syndrome is also associated with a variety of clinical conditions, including rheumatoid arthritis, obesity, hypothyroidism, diabetes mellitus, and pregnancy.^2-4 Acute carpal tunnel syndrome may occur as a result of a sudden increase in interstitial pressure within the canal, as in the case of distal radius fractures, hemorrhage into the canal, burns, or infection. Factors that may predispose patients to slowing of nerve conduction velocity and carpal tunnel syndrome include advancing age, overweight, female gender, and square-shaped wrists.⁵

Work-related overuse is a controversial cause of carpal tunnel syndrome, as incidence of carpal tunnel syndrome among computer users has been found to be similar to that in the general population.⁶ However, continuous typing or keyboard use at work appears to account for the condition in a large number of patients. Occupations with particular risk for carpal tunnel syndrome include those involving high force, repetitive tasks, prolonged wrist flexion, and/or use of vibrating equipment.

Clinical Presentation
Patients with carpal tunnel syndrome complain of pain, numbness, burning and/or tingling in the median nerve distribution. Paresthesias often occur at night and may wake patients from sleep. Discomfort can radiate into the forearm, elbow, and shoulder.

Symptoms are exacerbated by excessive wrist motion, and patients may report shaking their wrist in an attempt to restore normal sensation; this is known as the "flick sign."² Patients may describe difficulty with fine manipulation, decreased grip and pinching strength, increased clumsiness, and more frequent dropping of objects, especially as symptoms progress.

Physical Examination
Typically, physical examination findings are normal early in the course of the disease and in patients with mild intermittent symptoms. In severe and prolonged cases, flattening of the thenar eminence and atrophy of the thenar muscles may occur, causing weakness in thumb abduction and opposition.

Function of the opponens pollicis muscle can be evaluated by having the patient form a circle with the thumb and fifth finger, then testing his or her ability to resist breakthrough. The classic pattern of symptoms seen on hand diagrams (hypoalgesia and weak thumb abduction) have been found to be highly predictive of a positive result on a nerve conduction study.⁷

Phalen's maneuver(sensitivity, 68%; specificity, 73%) and Tinel's test (sensitivity, 50%; specificity, 77%)⁸ are the most common provocative tests used to confirm the diagnosis of carpal tunnel syndrome. Phalen's maneuver is performed by having the patient hold the wrists in maximum flexion for 30 to 60 seconds (see Figure 1). A positive test is indicated by reproduction of pain or paresthesias within the median nerve distribution.

Tinel's test is performed by tapping over the median nerve just proximal to the distal wrist crease (see Figure 2). The test is considered positive when a sensation of tingling or electric shock is elicited within the median nerve distribution.

The median nerve compression test (direct compression over the median nerve for 30 to 60 seconds) may also reproduce the patient's symptoms and can be a helpful adjunctive test. Two-point discrimination may be decreased; this is typically a finding in late-stage disease.

Diagnostic Studies
The diagnosis of carpal tunnel is established primarily by clinical features. Nerve conduction studies (NCS) may be helpful when the diagnosis is uncertain and to identify other sources of symptoms, such as cervical radiculopathy, other peripheral neuropathies, and other median nerve entrapment syndromes of the forearm.⁷

NCS are also indicated for severe cases with muscle atrophy and for preoperative planning to confirm the location of entrapment and to assess slowing of median nerve conduction velocity. Although consensus practice parameters jointly issued by the American Association of Electrodiagnostic Medicine, the American Academy of Neurology, and the American Academy of Physical Medicine and Rehabilitation recommend NCS for a confirmed diagnosis of carpal tunnel syndrome,⁹ it is reasonable to initiate treatment based on the presence of typical symptoms and exam findings.

Radiographic studies are not indicated for the diagnosis of carpal tunnel syndrome unless other bony sources of wrist and hand pain must be ruled out. While MRI may identify a lesion within the carpal tunnel and ultrasonography may suggest the diagnosis of tenosynovitis, advanced imaging is rarely used in the diagnosis or management of carpal tunnel syndrome. Specific laboratory studies should be performed if the potential for associated systemic diseases is a concern.

Management
The treatment of carpal tunnel syndrome involves interventions that attempt to alleviate pressure on the median nerve. Treatment measures vary according to severity of the disease, with both conservative and surgical options. Mild to moderate cases are initially treated with conservative measures, including workplace and ergonomic modifications, wrist splinting, NSAIDs, and local corticosteroid injections. Surgical release of the carpal tunnel should be considered for patients with severe cases (ie, those involving muscle weakness and atrophy) and in cases in which conservative measures are ineffective.

Workplace/Ergonomic Modifications
Although controversy persists over the association of workplace activities with the development of carpal tunnel syndrome, modifications to ensure proper body alignment, keyboard mechanics, and seat and desk height should be made. Instructions to limit excessive wrist flexion and to take frequent short breaks from repetitive wrist activities are also appropriate initial interventions. Workstation setup should be evaluated and adjusted to help avoid improper positioning that may provoke symptoms, especially for patients whose jobs require excessive computer or keyboard use. Use of vibrating tools also should be limited. Whenever possible, work tasks should be rotated and varied to help limit repetitive activities and exacerbation of symptoms.

Wrist Splinting
Wrist splinting helps maintain the wrist in a neutral position, preventing repetitive wrist flexion and rotation that may cause compression of the median nerve. Wrist splints may be purchased over the counter or custom-made by occupational therapists. These devices can be very helpful if worn at night, especially in patients with nighttime or morning symptoms. Daytime splinting for use during activities that involve repetitive wrist flexion is also appropriate.¹⁰ Significant improvement of symptoms may be seen after two to four weeks of splinting.¹¹

Oral Medications
NSAIDs and oral corticosteroids can be beneficial for patients with carpal tunnel syndrome. NSAIDs are often helpful for patients with an acute overuse etiology, soft tissue swelling, or tenosynovitis. Short-term use of oral corticosteroids has demonstrated improvement of symptoms within two to four weeks of treatment.^11,12 However, appropriate doses and efficacy for long-term use have not been established, and the potential for adverse effects makes oral corticosteroids a less desirable treatment option for long-standing cases.

Medications typically used in the setting of chronic nerve pain, such as gabapentin and amitriptyline, should be considered for recalcitrant and chronic cases. Diuretics have not been found effective.

Injections
Local corticosteroid injections may reduce inflammation within the carpal tunnel and can provide substantial clinical improvement. In comparisons with systemic injections or placebo at one month and with oral corticosteroids at three months, local injections were found to provide superior prolonged clinical relief of symptoms.^13,14

Several different techniques have been described to inject the carpal tunnel. The authors prefer a proximal approach to carpal tunnel injections (see Figure 3). In this approach, after sterile preparation, the needle is inserted 0.5 in to 0.75 in at a 45 to 60 angle, about 0.75 in proximal to the distal wrist crease and between the tendons of the flexor carpi radialis and palmaris longus muscles or ulnar to the palmaris longus tendon. A mixture of 0.5 mL corticosteroid (eg, triamcinolone 40 mg/mL) and 1.5 mL of 1% lidocaine, administered with a 30-gauge needle, is recommended. Care should be taken to avoid penetrating visible superficial veins. Any resistance or active paresthesias should prompt the withdrawal and redirection of the needle.

An alternative technique involves direct injection at the distal wrist crease, just ulnar to the palmaris longus tendon (or just ulnar to midline in patients without a palmaris longus tendon). The needle is inserted at a 45 angle, aiming toward the middle finger.

Risks include possible injection into the median nerve, intratendinous injection, tendon rupture, hypopigmentation, and skin atrophy.^2,14,15

Other Nonsurgical Options
Additional nonsurgical treatment options exist for patients whose symptoms do not respond to conservative measures. Physical or occupational therapy exercises and modalities that may be helpful for appropriate patients include carpal bone mobilization, nerve and tendon gliding techniques, and soft tissue mobilization.^16,17

Yoga postures designed for strengthening, stretching, and balance of the upper extremities may provide additional relief of symptoms.¹⁸ These can be considered for motivated patients.

Surgery
Surgical decompression is an effective treatment for carpal tunnel syndrome. Surgery can be performed as an open or an endoscopic procedure; the two have been demonstrated to provide comparable outcomes. The choice between these procedures is often dictated by the experience and preference of the surgeon.¹⁹ Carpal tunnel release should be considered in patients whose symptoms are severe or persist despite conservative treatment, and in those who have muscle weakness or atrophy.²

Conclusion
Carpal tunnel syndrome results from entrapment of the median nerve. This is a common cause of pain and paresthesias to the palmar aspect of the thumb and the index and middle fingers; and to the radial half of the ring fingers. The diagnosis of carpal tunnel syndrome is generally made by specific clinical features: the presence of paresthesias or sensory changes within the median nerve distribution, weakness of thumb abduction and opposition, and the presence of thenar muscle atrophy.

Initial conservative treatment with workplace, ergonomic, and activity modifications, and short-term use of NSAIDs and a neutral wrist brace are often effective. Local corticosteroid injection and formal physical or occupational therapy can also be helpful. Surgical referral is indicated in severe or recalcitrant cases or for patients who experience muscle weakness or atrophy.

References
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17. Akalin E, El O, Peker O, et al. Treatment of carpal tunnel syndrome with nerve and tendon gliding exercises. Am J Phys Med Rehabil. 2002;81:108-113.

18. Garfinkel MS, Singhal A, Katz WA, et al. Yoga-based intervention for carpal tunnel syndrome: a randomized trial. JAMA. 1998;280:1601-1603.

19. MacDermid JC, Richards RS, Roth JH, et al. Endoscopic versus open carpal tunnel release: a randomized trial. J Hand Surg [Am]. 2003;28:475-480.