Atlas of pathophysiology, 2 Edition

Part II - Disorders

Musculoskeletal disorders

Carpal tunnel syndrome

Carpal tunnel syndrome, a form of repetitive stress injury, is the most common of the nerve entrapment syndromes.

Age Alert

Carpal tunnel injury usually occurs in women between ages 30 and 60 and poses a serious occupational health problem.

Assembly-line workers and packers and people who repeatedly use poorly designed tools are also likely to develop this disorder. Computer keyboard and mouse users are also frequently affected. Any strenuous use of the hands—sustained grasping, twisting, or flexing—aggravates this condition.

Causes

Mostly idiopathic, or may result from:

·   repetitive stress injury

·   rheumatoid arthritis

·   flexor tenosynovitis (often associated with rheumatic disease)

·   nerve compression

·   pregnancy

·   multiple myeloma

·   diabetes mellitus

·   acromegaly

·   hypothyroidism

·   amyloidosis

·   obesity

·   benign tumor

·   other conditions that increase fluid pressure in the wrist, including alterations in the endocrine or immune systems

·   wrist dislocation or sprain, including Colles' fracture followed by edema.

Pathophysiology

The carpal bones and the transverse carpal ligament form the carpal tunnel. Inflammation or fibrosis of the tendon sheaths that pass through the carpal tunnel often cause edema and compression of the median nerve. This compression neuropathy causes sensory and motor changes in the median distribution of the hand, initially impairing sensory transmission to the thumb, index finger, second finger, and inner aspect of the third finger.

Signs and symptoms

·   Weakness, pain, burning, numbness, or tingling in one or both hands

·   Paresthesia in thumb, forefinger, middle finger, and half of the fourth finger

·   Inability to clench fist

·   Pain extending to forearm and, in severe cases, to shoulder

·   Pain usually relieved by shaking or rubbing hands vigorously or dangling arms

·   Symptoms typically worse at night and in the morning (Vasodilation, stasis, and prolonged wrist flexion during sleep may contribute to compression of the carpal tunnel.)

·   Possibly, atrophic nails

·   Dry, shiny skin

Diagnostic test results

·   Electromyography shows a median-nerve motor conduction delay of more than 5 milliseconds.

·   Digital electrical stimulation shows median nerve compression by measuring the length and intensity of stimulation from the fingers to the median nerve in the wrist.

Clinical Tip

These tests provide rapid diagnosis of carpal tunnel syndrome:

·   Tinel's sign—tingling over the median nerve on light percussion

·   Phalen's wrist-flexion test—holding the forearms vertically and allowing both hands to drop into complete flexion at the wrists for 1 minute reproduces symptoms of carpal tunnel syndrome

·   Compression test—blood pressure cuff inflated above systolic pressure on the forearm for 1 to 2 minutes provokes pain and paresthesia along the distribution of the median nerve.

Treatment

·   Conservative treatment—resting the hands by splinting the wrists in neutral extension for 1 to 2 weeks, along with gentle daily range-of-motion exercises

·   Nonsteroidal anti-inflammatory drugs for symptomatic relief

·   Injection of the carpal tunnel with hydrocortisone and lidocaine

·   Treatment of any underlying disorder

·   Surgical decompression of the nerve by resecting the entire transverse carpal tunnel ligament or by using endoscopic surgical techniques

·   Possibly, neurolysis (freeing of the nerve fibers)

·   Modification of the work area

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NERVE COMPRESSION IN CARPAL TUNNEL SYNDROME

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How carpal tunnel syndrome occurs

Flexion

Compression of nerve between tendons and transverse carpal ligament.

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Extension

Stretching of nerve over tendons and bones.

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