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INTRODUCTION — Carpal tunnel syndrome (CTS) refers to the complex of symptoms and signs brought on by compression of the median nerve as it travels through the carpal tunnel. Patients commonly experience pain and paresthesia, and less commonly weakness, in the median nerve distribution. CTS is the most frequent compressive focal mononeuropathy seen in clinical practice.
This topic will review the clinical manifestations and diagnosis of CTS. Other aspects of CTS are discussed separately. (See "Etiology of carpal tunnel syndrome" and "Treatment of carpal tunnel syndrome".)
CLINICAL FEATURES — The hallmark of classic CTS is pain or paresthesia (numbness and tingling) in a distribution that includes the median nerve territory, with involvement of the first three digits and the radial half of the fourth digit (figure 1). The symptoms of CTS are typically worse at night and often awaken patients from sleep. Some patients react to these symptoms by shaking or wringing their hands or by placing them under warm running water .
Although the sensory symptoms of CTS are usually limited to the median-innervated fingers, there is a wide range of variability. The pain and paresthesia may be localized to the wrist or involve the entire hand. It is not uncommon for sensory symptoms to radiate proximally into the forearm, and less frequently to radiate above the elbow to the shoulder .
CTS symptoms are often provoked by activities that involve flexing or extending the wrist or raising the arms, such as driving, reading, typing, and holding a telephone [1,2].
Bilateral CTS is common at first presentation, affecting up to 65 percent of patients . In some cases, involvement is subclinical on one side and symptomatic on the other.
The clinical course of CTS may follow an alternating pattern with periods of remission and exacerbation . In some cases, there is progression from intermittent to persistent sensory complaints in the hand as CTS worsens, and later to the development of motor symptoms in the hand.
In more severe cases of CTS, motor involvement leads to complaints of weakness or clumsiness when using the hands, such as difficulty holding objects, turning keys or doorknobs, buttoning clothing, or opening jar lids . Clinical signs may include weakness of thumb abduction and opposition, and atrophy of the thenar eminence.
Fixed sensory loss is usually a late finding characterized by a distinctive clinical pattern that involves the median-innervated fingers and spares the thenar eminence. This pattern occurs because the palmar sensory cutaneous nerve arises proximal to the wrist and passes over, rather than through, the carpal tunnel. (See "Etiology of carpal tunnel syndrome", section on 'Anatomy'.)
DIAGNOSIS — CTS is a clinical diagnosis. The diagnosis is suspected when the characteristic symptoms and signs are present. The most important of these are nocturnal pain or paresthesia in the distribution of the median nerve . (See 'Clinical features' above.)
The likelihood of the diagnosis is thought to correlate with the number of standard symptoms and provocative factors listed as criteria for the diagnosis of CTS :
Electrodiagnostic testing can be helpful to confirm or exclude CTS when the clinical diagnosis is uncertain . It is also useful to gauge severity of nerve compression and to aid in decisions regarding surgical intervention. (See 'Electrodiagnostic testing' below.)
The combination of characteristic symptoms and signs and confirmatory electrodiagnostic testing appears to be most accurate for the diagnosis of CTS [6,7].
Examination — Objective sensory and motor deficits corresponding to the median nerve-innervated regions of the hand may be present, but their absence does not rule out the diagnosis of CTS.
Sensation should be tested in all regions of the hand, forearm, and upper arm (figure 2). As mentioned above, sensory deficits usually occur late in the course of CTS; they involve the median-innervated fingers but spare the thenar eminence . This is a critical finding, as sensory loss over the thenar eminence suggests a median nerve lesion proximal to the carpal tunnel.
Objective weakness can occur in advanced CTS and is limited to muscles of the thenar eminence . This manifests principally as weakness of thumb abduction and thumb opposition. Atrophy of the thenar eminence may be present.
Provocative maneuvers — Provocative maneuvers for CTS include the Phalen, Tinel, manual carpal compression, and hand elevation tests. These can be helpful when interpreted in the proper clinical context. However, the sensitivity and specificity of these provocative tests is moderate at best [8,9].
Electrodiagnostic testing — Nerve conduction studies (NCS) and electromyography (EMG) are a standard part of the evaluation for CTS. They are useful to support the diagnosis of CTS, to assess severity, and to rule out other abnormalities . The diagnosis is primarily dependent on results from the NCS. The main utility of EMG is to exclude other conditions such as polyneuropathy, plexopathy, and radiculopathy .
Electrodiagnostic studies are essential if surgical treatment for CTS is being considered.
Nerve conduction studies — The electrodiagnosis of CTS rests upon the demonstration of impaired median nerve conduction across the carpal tunnel in the context of normal conduction elsewhere [1,14]. Nerve compression results in damage to the myelin sheath and manifests as delayed distal latencies and slowed conduction velocities. With sustained or more severe compression, axon loss may also occur, resulting in a reduction of the median nerve compound motor or sensory action potential amplitude.
The NCS evaluation for CTS involves measurement of conduction velocity across the carpal tunnel, as well as determination of the amplitude of sensory and motor responses. Mild CTS may not produce any nerve conduction abnormalities. With increased compression of the median nerve, focal demyelination can occur. This may result in local conduction block and/or slowing of motor and sensory conduction across the wrist. With even greater compression, the axons of the median nerve themselves can be damaged, resulting in reduced amplitudes. Sensory fibers seem to be more sensitive to compression than motor fibers. As a result, sensory fibers typically demonstrate changes on nerve conduction studies earlier than do motor fibers.
Sensory conduction studies may involve branches that innervate any of the first four digits, depending on clinical symptoms. Motor conduction studies most often record from the abductor pollicis brevis muscle, although other muscles can provide added information. Results obtained are compared to age-dependent normal values, as well as to other nerves of the same hand or the contralateral hand. In particular, the ulnar nerve and sometimes the radial nerve are also evaluated to ensure that any abnormalities seen in the median nerve are specific to that nerve and not part of a more widespread disorder, such as a peripheral neuropathy.
Routine NCS for the diagnosis of CTS typically include the following studies :
Additional comparison studies should be used for patients who have normal routine NCS in the setting of clinical findings suggestive of CTS . These include the following:
These methods compare the conductions of median fibers directly with ulnar fibers traveling in the same region. In a 2002 systematic review of prospective studies, the sensitivity of various NCS for CTS ranged from 56 to 85 percent, and the specificity ranged from 94 to 99 percent . In a later study of 99 patients meeting clinical criteria for CTS without confounding neurologic disorders, NCS (including median and ulnar palmar mixed-nerve studies) were normal in 25 percent .
Anomalous innervations are not uncommonly seen during electrodiagnostic testing. The one most frequently encountered in the arm is the Martin-Gruber anastomosis, which has a prevalence of 15 to 32 percent [16-18]. With this median-to-ulnar anastomosis, a subgroup of motor fibers split from the median nerve in the forearm and anastomose with the ulnar nerve as it travels through the forearm into the hand. The median-to-ulnar motor fibers that make up this anastomosis innervate the intrinsic muscles of the hand.
The Martin-Gruber anastomosis is most often identified during ulnar nerve testing. During median nerve motor studies, one may see a pattern where the amplitude of the compound muscle action potential is higher with stimulation at the proximal elbow site than with stimulation at the wrist . In the setting of median nerve entrapment at the wrist (CTS), a surprisingly fast median nerve conduction velocity in the forearm can be seen [18,19]. These electrodiagnostic findings are intuitive if one keeps in mind that not all median motor fibers are taking their normal route through the carpal tunnel. Instead, they are bypassing the site of entrapment by taking this circuitous route with the ulnar nerve.
Electromyography — As noted above, the electrodiagnosis of CTS depends mainly upon the demonstration of impaired median nerve conduction across the carpal tunnel. EMG is most useful to exclude other conditions, such as polyneuropathy, plexopathy, and radiculopathy .
The EMG portion of the electrophysiologic examination looks for evidence of pathologic changes in the muscles innervated by the median nerve, typically assessing the abductor pollicis brevis muscle. When secondary axonal loss is present, EMG may reveal either active denervation (eg, spontaneous activity such as fibrillation potentials, positive sharp waves, and fasciculation potentials) or chronic changes that indicate denervation with subsequent reinnervation (eg, changes in motor unit action potential amplitudes, durations, and recruitment)
Such findings are supportive of the diagnosis of CTS in the context of normal findings in both nonmedian-innervated muscles and proximal median nerve-innervated muscles.
One suggested protocol for EMG evaluation of CTS involves needle examination of the following muscles :
Additional muscles are investigated if the abductor pollicis brevis is abnormal :
Imaging — Imaging studies are not routinely employed in the evaluation for possible CTS. Several studies using ultrasonography have shown that patients with CTS have significantly increased cross-sectional area of the median nerve compared with controls [20-25]. However, the optimal cross-sectional area cutoff for the diagnosis, as well as the sensitivity and specificity of this technique, has varied in these reports [26,27]. In a systematic review of the literature published through May 2011, the four highest-quality studies used cutoffs of 8.5 to 10 mm2 for the diagnosis . The sensitivities ranged from 65 to 97 percent and the specificities ranged from 73 to 98 percent.
MRI can detect abnormalities of the median nerve, flexor tendons, vascular structures, and transverse carpal ligament in the region of the carpal tunnel [28,29]. However, the diagnostic utility of MRI for CTS remains uncertain. Thus, MRI is rarely ordered and is reserved for unusual cases to rule out a mass lesion.
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ACKNOWLEDGMENT — The author and editors would like to acknowledge Dr. Kevin Scott, who contributed to earlier versions of this topic review.
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