CARPAL TUNNEL SYNDROME

CARPAL TUNNEL SYNDROME

Carpal tunnel syndrome (CTS) is a collection of characteristic symptoms and signs that occurs following entrapment of the median nerve within the carpal tunnel.

Usual symptoms include numbness, paresthesias, and pain in the median nerve distribution. These symptoms may or may not be accompanied by objective changes in sensation and strength of median-innervated structures in the hand.

PATHOPHYSIOLOGY

Until the advent of electrophysiologic testing in the 1940s, carpal tunnel syndrome (CTS) commonly was thought to be the result of compression of the brachial plexus by cervical ribs and other structures in the anterior neck region.

It is now known that the median nerve is damaged within the rigid confines of the carpal tunnel, initially undergoing demyelination followed by axonal degeneration.

Sensory fibers often are affected first, followed by motor fibers. Autonomic nerve fibers carried in the median nerve also may be affected.

The cause of the damage is subject to some debate; however, it seems likely that abnormally high carpal tunnel pressures exist in patients with CTS. This pressure causes obstruction to venous outflow, back pressure, edema formation, and ultimately, ischemia in the nerve.

The risk of development of CTS appears to be associated, at least in part, with a number of different epidemiologic factors, including genetic, medical, social, vocational, avocational, and demographic.

A complex interaction probably exists between some or all these factors, eventually leading to the development of CTS. Definite causative factors, however, are far from clear.

FREQUENCY

The incidence of carpal tunnel syndrome is 1-3 cases per 1000 subjects per year; prevalence is approximately 50 cases per 1000 subjects in the general population.

SEX

The female-to-male ratio for carpal tunnel syndrome is 3-10:1.

AGE

The peak age range for development of carpal tunnel syndrome (CTS) is 45-60 years. Only 10% of patients with CTS are younger than 31 years.

CLINICAL

HISTORY

The patient's history often is more important than the physical examination in making the diagnosis of carpal tunnel syndrome (CTS).

• Numbness and tingling

  • Among the most common complaints, patients will reveal that their hands fall asleep or that things slip from their fingers without their noticing (loss of grip, dropping things); numbness and tingling also are commonly described.

  • Symptoms are usually intermittent and are associated with certain activities (eg, driving, reading the newspaper, crocheting, painting). Nighttime symptoms that wake the individual are more specific to CTS, especially if the patient relieves symptoms by shaking the hand/wrist. Bilateral CTS is common, although the dominant hand is usually affected first and more severely than the other hand.

  • Complaints should be localized to the palmar aspect of the first to the fourth fingers and the distal palm (ie, the sensory distribution of the median nerve at the wrist). Numbness existing predominantly in the fifth finger or extending to the thenar eminence or dorsum of the hand should suggest other diagnoses. A surprising number of CTS patients are unable to localize their symptoms further (eg, whole hand/arm feeling dead). This generalized numbness may indicate autonomic fiber involvement and does not exclude CTS from the diagnosis.

• Pain

  • The sensory symptoms above commonly are accompanied by an aching sensation over the ventral aspect of the wrist. This pain can radiate distally to the palm and fingers or, more commonly, extend proximally along the ventral forearm.

  • Pain in the epicondylar region of the elbow, upper arm, shoulder, or neck is more likely to be due to other musculoskeletal diagnoses (eg, epicondylitis) with which CTS commonly is associated. This more proximal pain also should prompt a careful search for other neurologic diagnoses (eg, cervical radiculopathy).

• Autonomic symptoms

  • Not infrequently, patients report symptoms in the whole hand. Many patients with CTS also complain of a tight or swollen feeling in the hands and/or temperature changes (eg, hands being cold/hot all the time).

  • Many patients also report sensitivity to changes in temperature (particularly cold) and a difference in skin color. In rare cases, there are complaints of changes in sweating. In all likelihood, these symptoms are due to autonomic nerve fiber involvement (the median nerve carries most autonomic fibers to the whole hand).

• Weakness / clumsiness - Loss of power in the hand (particularly for precision grips involving the thumb) does occur; in practice, however, loss of sensory feedback and pain is often a more important cause of weakness and clumsiness than is loss of motor power per se.

PHYSICAL

Clinical examination is important to rule out other neurologic and musculoskeletal diagnoses; however, the examination often contributes little to the confirmation of the diagnosis of carpal tunnel syndrome (CTS).

v  Sensory examination

o    Abnormalities in sensory modalities may be present on the palmar aspect of the first 3 digits and radial one half of the fourth digit. Semmes-Weinstein monofilament testing or 2-point discrimination may be more sensitive in picking this up; however, in the author's experience, pinprick sensation is as good as any test.

o    Sensory examination is most useful in confirming that areas outside the distal median nerve territory are normal (eg, thenar eminence, hypothenar eminence, dorsum of first web space).

v  Motor examination - Wasting and weakness of the median-innervated hand muscles (LOAF muscles) may be detectable.

o    L - First and second lumbricals

o    O - Opponens pollicis

o    A - Abductor pollicis brevis

o    F - Flexor pollicis brevis

v  Special tests - No good clinical test exists to support the diagnosis of CTS.

o    Hoffmann-Tinel sign

§  Gentle tapping over the median nerve in the carpal tunnel region elicits tingling in the nerve's distribution.

§  This sign still is commonly looked for, despite the low sensitivity and specificity.

o    Phalen sign

§  Tingling in the median nerve distribution is induced by full flexion (or full extension for reverse Phalen) of the wrists for up to 60 seconds

§  This test has 80% specificity but lower sensitivity.

o    The carpal compression test

§  This test involves applying firm pressure directly over the carpal tunnel, usually with the thumbs, for up to 30 seconds to reproduce symptoms.

§  Reports indicate that this test has a sensitivity of up to 89% and a specificity of 96%.

o    Palpatory diagnosis

§  This test involves examining the soft tissues directly overlying the median nerve at the wrist for mechanical restriction.

§  This palpatory test has been noted to have a sensitivity of over 90% and a specificity of 75% or greater.

o    The square wrist sign

§  The ratio of the wrist thickness to the wrist width is greater than 0.7.

§  This test has a modest sensitivity/specificity of 70%.

v  Several other tests have been advocated, but they rarely provide additional information beyond that which the Phalen and square wrist signs provide.

CAUSES

Note that carpal tunnel syndrome (CTS) is associated with many different factors.

In particular, the more the hand and wrist are used, the greater the symptoms.

This observation does not necessarily mean that using the hand and wrist causes the syndrome or that more median nerve damage ensues. Association should not be assumed to signify causation.

• Demographics

  • Increasing age

  • Female sex

  • Increased body mass index (BMI), especially a recent increase

  • Square-shaped wrist

  • Short stature

  • Dominant hand

  • Race (white)

• Genetics

  • A strong family susceptibility exists and is probably related to multiple inherited characteristics (eg, square wrist, thickened transverse ligament, stature).

  • A number of inherited medical conditions also are associated with CTS (eg, diabetes, thyroid disease, hereditary neuropathy with liability to pressure palsies).

• Medical conditions

  • Wrist fracture (Colles)

  • Acute, severe flexion/extension injury of wrist

  • Space-occupying lesions within the carpal tunnel (eg, flexor tenosynovitis, ganglions, hemorrhage, aneurysms, anomalous muscles, various tumors, edema)

  • Diabetes

  • Thyroid disorders (usually myxedema)

  • Rheumatoid arthritis and other inflammatory arthritides of the wrist

  • Recent menopause (including post-oophorectomy)1

  • Renal dialysis

  • Acromegaly

  • Amyloidosis

• Vocational / avocational - Activities that may be associated with CTS (particularly in combination) involve the following:

  • Prolonged, severe force through the wrist

  • Prolonged, extreme posture of the wrist

  • High amounts of repetitive movements

  • Exposure to vibration and/or cold

• Other factors

  • Lack of aerobic exercise

  • Pregnancy and breastfeeding

  • Use of wheelchairs and/or walking aids 

DIAGNOSIS

LABORATORY STUDIES

• No blood tests exist for the diagnosis of carpal tunnel syndrome; however, laboratory testing for associated conditions (eg, diabetes) may be performed when clinically indicated.

IMAGING STUDIES

• No imaging studies are considered routine in the diagnosis of carpal tunnel syndrome (CTS).

  • Magnetic resonance imaging (MRI) of the carpal tunnel is particularly useful preoperatively if a space-occupying lesion in the carpal tunnel is suggested. Signal abnormality can be detected in the median nerve in some cases of CTS, but how these abnormalities correlate to diagnosis and physiologic severity is not clear. MRI does not rule out the multitude of other differential diagnoses and is time consuming and resource intensive.

  • Ultrasonography potentially can pick up some space-occupying lesions in the carpal tunnel. Problems differentiating the median nerve from surrounding soft tissue (particularly distally) severely limit its role in diagnosis at present.

OTHER TESTS

• Electrodiagnosis

  • Electrophysiologic studies, including electromyography (EMG) and nerve conductions studies (NCS), are the first-line investigations in suggested carpal tunnel syndrome (CTS). Abnormalities on electrophysiologic testing, in association with specific symptoms and signs, are considered the criterion standard for CTS diagnosis. In addition, other neurologic diagnoses can be excluded with these test results.

  • Electrophysiologic testing also can provide an accurate assessment of how severe the damage to the nerve is, thereby directing management and providing objective criteria for the determination of prognosis. CTS is usually divided into mild, moderate, and severe; however, criteria for this assessment usually vary from lab to lab. In general, patients with mild CTS have sensory abnormalities alone on electrophysiologic testing, and patients with sensory plus motor abnormalities have moderate CTS. However, any evidence of axonal loss (eg, decreased or absent sensory or motor responses distal to the carpal tunnel or neuropathic abnormalities on needle EMG) is classified as severe CTS.

  • Changes in electrophysiologic results over time can be used to assess the success of various treatment modalities.

• The American Association of Electrodiagnostic Medicine has published standards and guidelines that govern the minimum number of studies that should be performed to diagnose CTS.

• Other quantitative tests, such as thermography and vibrometry, have been shown to be inferior to electrophysiologic examination and, because they have not been supported by controlled studies, are not recommended.

TREATMENT

PHYSICAL THERAPY

Given that carpal tunnel syndrome (CTS) is associated with low aerobic fitness (and increased BMI), it makes inherent sense to provide the patient with an aerobic fitness program.

Stationary biking, cycling, or any other exercise that puts strain on the wrists probably should be avoided.

The use of modalities (eg, ultrasonography, phonophoresis, iontophoresis) may provide relief in some patients.

Interestingly, it may be possible to enlarge the carpal tunnel by specific stretching techniques. Such an exercise program may provide a new noninvasive treatment for CTS in the future.

OCCUPATIONAL THERAPY

Work-site ergonomic assessment may help to reduce potentially exacerbating factors (eg, poor posture, excessive force).

Manufacture of a wrist-hand orthosis with the wrist joint in neutral (to be worn at nighttime for a minimum of 3-4 weeks) is one of the best evidence-based conservative treatments for carpal tunnel syndrome (CTS).

A specific stretching/strengthening program for the hand and wrist may be useful in improving strength and dexterity (particularly following surgical treatment), although it can exacerbate symptoms.

COMPLICATIONS

Most individuals with mild-to-moderate carpal tunnel syndrome (CTS; according to electrophysiologic data) respond to conservative management, usually consisting of splinting the wrist at nighttime for a minimum of 3 weeks.

Many off-the-shelf wrist splints seem to work well, although theoretically, a custom-made splint in neutral is probably the best choice. Nonsteroidal anti-inflammatory drugs (NSAIDs) and/or diuretics may be of benefit.

Steroid injection into the carpal tunnel is of benefit, as is oral prednisone (although injection rarely is used in practice).

Lack of aerobic exercise (along with increased BMI) is a risk factor for the development of CTS and should be addressed.

Overuse of legal drugs (eg, caffeine, nicotine, alcohol) can contribute to CTS and should therefore be reduced.

SURGICAL INTERVENTION

Patients whose condition does not improve following conservative treatment and patients who initially are in the severe carpal tunnel syndrome (CTS) category (as defined by electrophysiologic testing) should be considered for surgery.

Surgical release of the transverse ligament provides high initial success rates (greater than 90%), with low rates of complication; however, it has been suggested that the long-term success rate may be much lower than previously thought (approximately 60% at 5 y).

OTHER TREATMENT

Steroid injection into the carpal tunnel has been shown to be of long-term benefit and may be worthwhile prior to surgical management or in cases in which surgery is relatively contraindicated (eg, because of pregnancy).

Techniques and devices to stretch or manipulate the carpal tunnel have shown some promise but still are not accepted widely.

Laser therapy also has shown some early promise.

MEDICATION

Short (1-2 wk) courses of regular NSAIDs can be of benefit, particularly if there is any suggestion of inflammation in the wrist region (eg, flexor tenosynovitis, rheumatoid arthritis). Likewise, if edema is thought to be prominent, then a short course of a mild diuretic may be of benefit.

NONSTEROIDAL ANTI-INFLAMMATORY DRUGS

NSAIDs provide pain relief and reduction of inflammation. Reducing inflammation in the structures passing through the carpal tunnel decreases pressure and provides some relief to the compressed nerve. 

IBUPROFEN (Ibuprin, Motrin)

DOC for patients with mild to moderate pain. Inhibits inflammatory reactions and pain by decreasing prostaglandin synthesis.

Adult: 200-400 mg PO q4h; not to exceed 1200 mg in 24 h

Pediatric:

<2 years: 5 mg/kg PO q6h; not to exceed 3 doses in 24 h

2-12 years: 10 mg/kg PO q6h; not to exceed 3 doses in 24 h

>12 years: Administer as in adults

Pregnancy

C - Fetal risk revealed in studies in animals but not established or not studied in humans; may use if benefits outweigh risk to fetus

D - Fetal risk shown in humans; use only if benefits outweigh risk to fetus

Precautions

Caution in congestive heart failure, hypertension, and decreased renal and hepatic function; caution in anticoagulation abnormalities or during anticoagulant therapy

CYCLOOXYGENASE-2 INHIBITORS

Although increased cost can be a negative factor, the incidence of costly and potentially fatal GI bleeds is clearly less with COX-2 inhibitors than with traditional NSAIDs. Ongoing analysis of cost avoidance of GI bleeds will further define the populations that will find COX-2 inhibitors the most beneficial. 

CELECOXIB (Celebrex)

Inhibits primarily COX-2. Considered an inducible isoenzyme, COX-2 is induced during pain and inflammatory stimuli. Inhibition of COX-1 may contribute to NSAID GI toxicity. At therapeutic concentrations, COX-1 isoenzyme is not inhibited; thus, GI toxicity may be decreased. Seek lowest dose of celecoxib for each patient.

Adult: 200 mg PO qd (or 100 mg bid)

Pregnancy

C - Fetal risk revealed in studies in animals but not established or not studied in humans; may use if benefits outweigh risk to fetus

Precautions

Long-term administration may cause renal dysfunction; acute renal failure may be precipitated particularly in dehydration; may cause persistent urinary symptoms, cystitis, and hematuria; hepatic failure; congestive heart failure; hyperkalemia; anemia; rare blood dyscrasias; blurred or diminished vision; drowsiness, dizziness, vertigo, or insomnia may occur

DIURETIC AGENTS

Conditions that cause edema may increase pressure in the carpal tunnel. Diuretics may be beneficial in reducing edema. 

HYDROCHLOROTHIAZIDE (Esidrix, HydroDIURIL, Microzide)

Inhibits reabsorption of sodium in distal tubules, causing increased excretion of sodium and water, as well as potassium and hydrogen ions.

Adult: 25-200 mg PO qd or divided bid/tid

Pediatric: 2 mg/kg/d PO divided bid.