36: Median Neuropathy (Carpal Tunnel Syndrome)

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CHAPTER 36

Median Neuropathy (Carpal Tunnel Syndrome)

Meijuan Zhao, MD

David T. Burke, MD, MA

Synonyms

Median nerve entrapment at the wrist or carpal tunnel syndrome

Median nerve compression

ICD-9 Code

354.0  Carpal tunnel syndrome

ICD-10 Codes

G56.00  Carpal tunnel syndrome, unspecified upper limb

G56.01  Carpal tunnel syndrome, right upper limb

G56.02  Carpal tunnel syndrome, left upper limb

Definition

Carpal tunnel syndrome (CTS), an entrapment neuropathy of the median nerve at the wrist, is the most common compression neuropathy of the upper extremity. This syndrome produces paresthesias, numbness, pain, subjective swelling, and, in advanced cases, muscle atrophy and weakness of the areas innervated by the median nerve. The condition is often bilateral, although the dominant hand tends to be more severely affected.

CTS is thought to result from a compression of the median nerve as it passes through the carpal tunnel. The clinical presentation is variable. Whereas there is some variation as to what should be included in this definition, CTS is most often thought to involve sensory changes in the radial 31⁄2 digits of the hand with burning, tingling, numbness, and a subjective sense of swelling. Those affected often first note symptoms at night. In the later stages, complaints include motor weakness in the thenar eminence.

It is helpful to think of the carpal tunnel as a structure with four sides, three of which are defined by the carpal bones and the fourth, the “top” of the tunnel, by the transverse carpal ligament (Figs. 36.1 and 36.2). Passing through the tunnel are the median nerve and nine tendons with their synovial sheaths; these include the flexor pollicis longus, the four flexor digitorum superficialis, and the four flexor digitorum profundus tendons. None of the sides of the tunnel yields well to expansion of the fluid or structures within. Because of this, swelling will increase pressure within the tunnel and may result in compression of the median nerve. CTS occurs more commonly in women than in men, with a prevalence in the general adult population ranging from 2.7% to 5.8% [1,2]. It is most common in middle-aged persons between the ages of 30 and 60 years. The older adults may have objective clinical and electrophysiologic evidence of a more severe median nerve entrapment [3]. Most cases of CTS are idiopathic with congenital predisposition. Some focal or systemic conditions, such as wrist injury, arthritis, diabetes, thyroid disease, rheumatoid arthritis, and pregnancy, can increase pressure on the median nerve in the carpal tunnel and contribute to the development of CTS. Prolonged postures in extremes of wrist flexion or extension, repetitive use of the flexor muscles, and exposure to vibration are the primary exposures that have been reported [47]. The pathophysiologic mechanism of CTS involves a combination of mechanical trauma, increased pressure, and ischemic injury to the median nerve within the carpal tunnel [8].

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FIGURE 36.1 Radiographic demonstration of the carpal tunnel (for orientation, the hand is in the same position in the radiograph). The carpal tunnel is formed radially, ulnarly, and dorsally by the carpal bones. (From Concannon M. Common Hand Problems in Primary Care. Philadelphia, Hanley & Belfus, 1999.)
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FIGURE 36.2 The volar carpal ligament (line) forms the roof of the carpal tunnel. This thick, fibrous structure does not yield to expansion, and increased pressure within the carpal tunnel can cause impingement of the median nerve. (From Concannon M. Common Hand Problems in Primary Care. Philadelphia, Hanley & Belfus, 1999.)

Symptoms

The classic symptoms of CTS include numbness and paresthesias in the radial 31⁄2 fingers (Fig. 36.3). A typical early complaint is awakening in the night with numbness or pain in the fingers. Symptoms during the day are often brought out by activities placing the wrist in substantial flexion or extension or requiring repetitive motion of the structures that traverse the carpal tunnel. Many patients report symptoms outside the distribution of the median nerve as well [9]. Numbness and pain in the hand may also be accompanied by volar wrist pain and aching at the forearm. The patient may describe the symptoms as being positional, with symptoms relieved by the shaking of a hand, often referred to as the flick sign [10].

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FIGURE 36.3 Patients with carpal tunnel syndrome complain of numbness or paresthesia within the median nerve distribution (orange area, arrows). (From Concannon M. Common Hand Problems in Primary Care. Philadelphia, Hanley & Belfus, 1999.)

Patients may complain of a sense of swelling in the hands, often noting that they have difficulty wearing jewelry or watches, with this sensation fluctuating throughout the day or week. Some patients also report dry skin and cold hands. In the later stages of CTS, the numbness may become constant and motor disturbances more apparent, with complaints of weakness manifested by a functional decrease of strength. Patients may then report dropping objects.

Physical Examination

A two-point sensory discrimination test is thought to be the most sensitive of the bedside examination techniques. This involves a comparison of the two-point discriminating sensory ability of the median with that of the ulnar nerve distribution of the hand. Careful observation of the hands, comparing the affected side with the unaffected side and comparing the thenar and hypothenar eminences of the same hand, may reveal an increasing asymmetry. Weakness of the thenar intrinsic muscles of the hand can be tested with a dynamometer or clinically by testing abduction of the thumb against resistance. The more common special tests include the Phalen, the Tinel, and the nerve compression tests. The Phalen test involves a forced flexion at the wrist to 90 degrees for a period of 1 minute; a positive test result reproduces the symptoms of CTS (Fig. 36.4). The reverse Phalen maneuver is the same test completed with forced extension. The Tinel test involves tapping sharply over the volar aspect of the wrist just distal to the distal wrist crease. The test result is positive when a sensory disturbance radiates down the region of the distribution of the median nerve. The nerve compression test involves the placement of two thumbs over the roof of the carpal tunnel, with pressure maintained for 1 minute. The test result is positive if symptoms are reproduced in the area of the distribution of the median nerve. A review showed an overall estimate of 68% sensitivity and 73% specificity for the Phalen test, 50% sensitivity and 77% specificity for the Tinel test, and 64% sensitivity and 83% specificity for the carpal compression test [11]. Two-point discrimination and testing of atrophy or strength of the abductor pollicis brevis proved to be specific but not very sensitive. [11].

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FIGURE 36.4 Phalen test. Patients maximally flex both wrists and hold the position for 1 to 2 minutes. If symptoms of numbness or paresthesia within the median nerve distribution are reproduced, the test result is positive. (From Concannon M. Common Hand Problems in Primary Care. Philadelphia, Hanley & Belfus, 1999.)

Functional Limitations

Functional limitations of CTS often include difficulty with sleep due to frequent awakenings by the symptoms. Because certain sustained or repetitive motions are difficult, tasks that often become more difficult include driving a car and sustained computer keyboard or mouse use at work. The later symptom of weakness in the thenar eminence may result in difficulty maintaining grip. Profound CTS may result in functional limitations, such as the inability to tie one’s shoes, to button shirts, and to put a key in a lock.

Diagnostic Studies

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