Abstract
Carpal tunnel syndrome is the most common entrapment neuropathy in the upper extremity.
Keywords
Carpal tunnel syndrome, diagnosis, splint, steroid injection, surgery
| Synonyms | |
| |
| 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 3½ 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%. 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. 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. Increasing BMI is a strong risk factor for CTS : being overweight increases the risk by 1.5 times, and being obese increases the risk by 2 times. High hand or wrist repetition rate is another risk factor for CTS. However, the role of computer keyboard or mouse use in contributing to CTS remains controversial. One recent meta-analysis showed no association between keyboard use and CTS, while another showed excessive computer use (particularly mouse use) to be a minor risk factor for CTS.
Prolonged postures in extremes of wrist flexion or extension, repetitive use of the flexor muscles, and exposure to vibration are the primary exposures reported. The pathophysiologic mechanism of CTS involves a combination of mechanical trauma, increased pressure, and ischemic injury to the median nerve within the carpal tunnel.
Symptoms
The classic symptoms of CTS include numbness and paresthesias in the radial 3½ 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. 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.
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 presence of thenar atrophy is strongly associated with CTS, but absence of thenar atrophy cannot exclude the diagnosis of CTS.
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. It is not recommended, however, to use the Phalen or Tinel test in isolation to diagnose CTS, as each test alone is poorly associated with ruling-in or ruling-out CTS. 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. Two-point discrimination and testing of atrophy or strength of the abductor pollicis brevis proved to be specific but not very sensitive.
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
Whereas CTS is a syndrome rather than a singular finding, it is often suggested that the “gold standard” test of CTS is electrodiagnostic testing. Electromyography and nerve conduction studies can confirm the diagnosis, determine the severity (if any) of nerve damage, guide and measure the effect of treatment, and rule out other conditions such as radiculopathy, polyneuropathy, and brachial plexopathy. Ultrasound studies, which reveal an enlarged median nerve, may assist with the diagnosis. Typically, the ultrasound examination may show flattening of the nerve within the tunnel and enlargement of the nerve proximal and distal to the tunnel. Pooling of recent articles seems to confirm that sonography using cross-sectional area of the median nerve could not be an alternative to electrodiagnostic testing for diagnosis of CTS, but could give complementary results. Limitations to ultrasound use include examiner experience, dependent intra-rater reliability in measurement of the median nerve, and a lack of consensus in diagnostic thresholds and ideal locations for ultrasound measurement. Though ultrasound should not be used routinely in diagnosis of CTS, ultrasound examination should be considered in doubtful cases or secondary cases of CTS.
Others have advocated the diagnostic injection of corticosteroids or bupivacaine into the carpal tunnel. If the injection is accompanied by a relief of symptoms, it provides diagnostic evidence of CTS.
A wrist radiograph may be helpful if a fracture or degenerative joint disease is suspected.
Blood tests should be ordered if underlying rheumatologic disease or endocrine disturbance is suspected. These include fasting blood glucose concentration, erythrocyte sedimentation rate, thyroid function, and rheumatoid factor. MRI is not sensitive for a diagnosis of CTS and is not routinely recommended.
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