Carpal tunnel syndrome (CTS) is the most common upper-extremity entrapment neuropathy.1 Entrapment neuropathies are caused by compression of a short segment of a single nerve at a specific site, usually as the nerve passes through a fibro-osseous tunnel.2 In CTS, the increased pressure and compression on the median nerve in the carpal tunnel and impaired nerve perfusion cause discomfort and paresthesia in the affected hand3 (Figure 1).
ETIOLOGY AND PATHOPHYSIOLOGY
Carpal tunnel syndrome is an isolated mononeuropathy affecting the upper distal extremities. The pathophysiology has been described as increased intracarpal pressure.3 Some common factors associated with development of CTS can be congenital or occupational; they also include female gender, pregnancy, diabetes, and benign tumors. As many as 50% of CTS cases are idiopathic.4Table 1 lists more comprehensive causes of CTS.
Congenital predisposition is the most common cause of CTS. Formed anteriorly by the flexor retinaculum and posteriorly by the carpal bones,5 the carpal tunnel houses the median nerve and flexor tendons of the fingers and is thought to be smaller in some people than in others.6 When the median nerve is compressed because of less space in the carpal tunnel, patients may develop neuropathic symptoms.
Occupational factors have been increasingly associated with the development of CTS, which is becoming one of the fastest growing occupational disorders in the United States.7 Working-age people whose occupations involve forceful movements of the hand and wrist or who use handheld, powered, vibratory tools are at higher risk for developing CTS.7 Additionally, people whose work involves repetitive motion—such as those who work on an assembly line, receptionists, seamstresses, musicians, and painters— are more likely to develop CTS.6 Although these occupations do not require forceful movement, they do involve constant extension and flexion of the tendons in the wrist, actions that cause fibrosis of the extensor retinaculum and entrapment of the median nerve.8
Females are 3 times more likely than males to develop CTS.6 Although scientific evidence is scant, two hypotheses have been proposed.6 First, similar to a congenital predisposition, the carpal tunnel in women may be smaller than in men.6 Second, researchers are studying whether genetics makes development of musculoskeletal diseases more likely in women than men.9 There is evidence that CTS affects approximately 62% of pregnant women, most often in the third trimester, although the disorder can occur in the first trimester.10
Diabetes mellitus has been associated with CTS. Whether they are the result of insufficient insulin production or improper response to the insulin that is produced, persistently elevated blood glucose levels can damage the nerves by injuring the walls of the capillaries that nourish them.11 For this reason, people with diabetes tend to develop nerve compressions, with carpal tunnel being one of the most common of these entrapment neuropathies. Research suggests that insulin resistance is also a risk factor, with blood glucose levels being significantly higher in patients with CTS.4
Benign tumors, though rare, have been associated with development of CTS.12 In one case report, a 32-year-old male manual laborer with a 2-year history of numbness, tingling, and burning pain in the palmar surface of the left hand and fingers was treated for CTS with surgery. Three months following surgery, his symptoms returned, and an MRI revealed a mass with well-defined margins and an ovoid shape located deep in the palm. The mass was identified as a leiomyoma, a very rare benign smooth muscle tumor.12,13 Leiomyomas may arise from deep soft tissue and affect men and women equally.13 In one study, spaceoccupying lesions in patients with unilateral carpal tunnel syndrome were detected in just 5.5% of patients because routine imaging is not necessarily done.12
SIGNS AND SYMPTOMS
Carpal tunnel syndrome is a progressive condition in which symptoms often start gradually. Patients may complain initially of frequent burning, tingling, or itching numbness in the palm of the hand, thumb, index and middle fingers, and on the thumb side of the ring finger.6 Nighttime pain in these areas may be especially predictive of CTS.14 Patients often report waking up in middle of night and having to “shake out” their hand(s).6 As the condition worsens, symptoms progress and may occur during the day and at night. Other symptoms include a sensation of digital swelling (although none may be evident), general weakness of the hand, numbness in the fingertips, and weakness of hand grip.15 Prolonged compression of the median nerve can cause permanent nerve damage, resulting in inability to distinguish between hot and cold temperatures and thenar eminence atrophy, which is atrophy of the muscle under the thumb.16 If atrophy is severe enough, the thumb cannot be pronated.16
A patient suspected of having CTS should have a physical examination and electrodiagnostic studies. The earliest possible diagnosis and treatment are important to avoid permanent damage to the median nerve. History-taking for possible CTS should include the basic questions about onset and severity of symptoms, palliative/ provocative factors, and quality and radiation of pain. Additional queries should focus on recent trauma, neck pain, distinguishing between wrist/hand pain or stiffness and paresthesia or numbness and tingling in the first 3.5 digits.16
After obtaining a thorough history, the practitioner should perform a complete physical examination, with particular attention to the area between the neck and the hand. Examination of the neck/cervical spine includes inspection for swelling, ecchymosis, and surgical scars; palpation for tenderness of spinous process or paraspinal muscles; testing of range of motion (ROM); strength testing; assessment of sensory and motor nerves; and special tests, including Tinel sign, Phalen maneuver, and the wrist-flexion provocative test.
Tinel sign is performed by percussing over the median nerve at the wrist to elicit a pins-and-needles sensation in the distribution of the median nerve from the wrist to the hand.16 This test is the least sensitive but most specific.16 The Phalen maneuver is performed by resting both elbows on a table and placing the wrists into volar flexion for at least 1 minute. Production of wrist paresthesia indicates a positive result. The Phalen maneuver is the most sensitive of the three tests.16 The wrist-flexion provocative test is performed by flexing the wrist and compressing the median nerve simultaneously.16 A positive result is reproduction of the patient's symptoms within 20 seconds. This test is 82% sensitive and 99% specific for CTS.17 Last, the practitioner may inspect for thenar muscle atrophy, by checking thumb opposition, which in a healthy patient would tighten the thenar muscle. In severe CTS, the abductor pollicis brevis muscle is atrophied.16 The abductor pollicis brevis is assessed with the arm in supination (palm facing the ceiling), making sure the hand is stabilized except for the thumb. The patient is asked to abduct the thumb (move the thumb toward the inside of the palm) against resistance from the examiner.18
CTS may be confirmed with electrodiagnostic studies, such as electromyography (EMG)/nerve conduction studies (NCS); plain film radiography; MRI; and ultrasonography. In most cases, plain film radiographs of the wrist/hand are done initially to rule out other diagnoses, such as osteoarthritis or fractures.6 Although no gold standard diagnostic test exists, EMG and NCS, which are often performed at same time, are most reliable.
EMG is performed by inserting a fine needle into a muscle and viewing the electrical activity of the muscle on a screen to determine the severity of damage to the median nerve.6 Prolonged sensory and motor latency confirm CTS.19 Prolonged sensory latency is the most sensitive and earliest indicator of CTS.19
Nerve conduction studies use electrodes on the extremity to deliver electric shocks to a nerve to determine the speed with which the nerve transmits impulses.6 CTS is present when median nerve conductional velocity is less than 50m/s.19 EMG and NCS are useful to distinguish among various diagnoses, including CTS, cervical radiculopathy, and ulnar neuropathy.
For recurrent CTS that does not resolve even after carpal tunnel release, MRI may be used to assess the size of the carpal tunnel and the adequacy of the release and to determine the position of the median nerve and leading flexor tendon within the carpal tunnel.20 In a small percentage of recurrent CTS cases, MRI may identify a rare underlying cause, such as a space-occupying lesion.20
Ultrasonography can be used to measure an increase in size of the median nerve in patients with suspected CTS. However, ultrasonography cannot solely be used as an alternative to electrodiagnostic studies since it is operatordependent.
Before CTS can be diagnosed, it must be distinguished from other causes of sensory and motor abnormalities that can affect the upper extremities. Various neuropathies and radiculopathies have the same or similar symptoms, including cervical spine pain with radiculopathy; wrist tendinitis; thoracic outlet syndrome (TOS); polyneuropathy; thumb carpometacarpal arthritis; and DeQuervain disease, an inflammatory tenosynovitis.
Neck pain with radiculopathy due to cervical root impingement or herniated nucleus pulposus can mimic signs of CTS. Cervical radiculopathy manifests with pain, numbness, and tingling or weakness that travels from the neck down the arm, forearm, and into the hand.21 In the cervical spine, the C5-C6 disk and the C6-C7 disk are most likely to herniate.22 Nerve root impingement at the C5-C6 disk may cause weakness of the biceps muscle and numbness to the thumb side of the hand,23 while impingement at the C6-C7 disk may cause weakness of the triceps muscle and numbness and tingling into the middle finger.24
Wrist tendinitis is inflammation or overuse of wrist tendons, most commonly as a result of repetitive strain. Wrist tendinitis may cause forearm and wrist pain, decreased ROM, sharp/ shooting pain, and numbness in the hand and fingers.25
Thoracic outlet syndrome is a comprehensive term encompassing three syndromes that can cause pain in the neck, shoulder, and arm. Neurogenic TOS involves compression of the brachial plexus, vascular TOS involves compression of the subclavian artery or vein, and nonspecific TOS is characterized by pain in the upper extremity from unidentified sources.26 Thoracic outlet syndrome typically causes shoulder pain or supraclavicular pain but also has symptoms that can resemble carpal tunnel syndrome, including “pins-and-needles” sensation throughout the hand and thenar atrophy.26,27
Polyneuropathy occurs when multiple widespread nerves throughout the body are damaged. Patients can experience sensory and motor neuropathy that affects their ability to feel and move, respectively.28 Polyneuropathy typically affects more than one part of the body, predominantly the lower extremities. Polyneuropathy is differentiated from CTS by EMG that demonstrates widespread, symmetrical, length-dependent neuropathies without isolated focal abnormalities in the median nerve. Polyneuropathies tend to be more common in patients with diabetes mellitus and those who abuse alcohol.11
Thumb carpometacarpal arthritis, also referred to as basal joint arthritis, is a progressive disease or wearing away of the articular cartilage. Patients may experience pain and stiffness of the thumb, difficulty pinching or grasping, and night pain.29 The base of the thumb is the most commonly involved arthritic joint in the hand.30 Women, especially those older than 45 years, are affected more often than men.29 In contrast with CTS, carpometacarpal arthritis is evident on radiography and produces normal results on EMG.
DeQuervain disease is an inflammation of the tendons (extensor pollicis brevis and abductor pollicis brevis) of the first extensor compartment that control movement of the thumb.31 The inflammation causes thickening and stenosis of the compartment's synovial sheath, resulting in pain in the tendons that pass through it. Patients may experience pain, especially over the radial styloid; swelling on the thumb side of the wrist; difficulty grasping objects; numbness in thumb and index finger; and positive results on the Finkelstein test.31 DeQuervain disease is caused by extra stress on the tendons and is most often seen in new mothers and patients who have suffered a wrist fracture.31 Unless the patient also has CTS, patients with DeQuervain disease will have normal results on EMG.32,33
- Patients may complain initially of frequent burning, tingling, or itching numbness in the palm of the hand, thumb, index and middle finger, and on the thumb side of the ring finger. Nighttime pain in these areas may be especially predictive of CTS.
- Prolonged compression of the median nerve can cause permanent nerve damage, resulting in inability to distinguish between hot and cold temperatures and thenar eminence atrophy.
- Prolonged sensory and motor latency on electromyography confirm CTS. prolonged sensory latency is the most sensitive and earliest indicator. On nerve conduction studies, median nerve conductional velocity less than 50 m/s is indicative of CTS.
- Treatment options include splinting, physical therapy, NSAIDs, and corticosteroid injection. refractory cases of CTS may be treated with open or endoscopic surgical techniques.
Both conservative and surgical treatment options exist for CTS. The least invasive treatment should be initiated first. Patients are advised to rest the affected extremity and to avoid any activities that worsen symptoms. If there is no relief or reduction of symptoms, surgical release provides more definitive treatment.6
Conservative treatment includes splinting, anti-inflammatory medications, corticosteroid injections, and physical therapy.6 Along with educating patients on activity modification and advising them to avoid repetitive wrist motions, wrist splinting is the least invasive and usual first step in treating CTS. Immobilizing the wrist in a neutral position with a removable cock-up wrist splint or volar splint reduces carpal tunnel pressure on the median nerve. Normal blood supply to the nerve may resume, and the patient may experience regression of CTS symptoms.3 Patients are typically instructed on nighttime use of splints because most people tend to sleep in a fetal position, which results in more pressure on the median nerve.34 Studies suggest that nighttime splinting is effective but only in early CTS.35
Oral medications are also used as first-line treatment of CTS, with oral NSAIDs the agents of choice.6 Anti-inflammatory medications, such as naproxen or celecoxib, are used to decrease the swelling in the carpal tunnel, thereby reducing the pressure on the median nerve.6
If patients do not experience relief from their symptoms through splinting and oral medications, 1 cc of a corticosteroid (dexamethasone) and 1 cc of a local anesthetic (mepivacaine) administered directly into the carpal tunnel may reduce swelling and pain. Randomized controlled trials have shown that local corticosteroid injections are effective only for short-term treatment of CTS.36
Other conservative treatments include exercise and therapy. Patients have experienced relief with physical therapy and occupational exercises to stretch and strengthen their upper extremities.6 Acupuncture and yoga also can reduce pain and improve grip strength.6
Surgical treatment is typically reserved for refractory cases of CTS when conservative measures have failed. The goal of surgery is to reduce pressure on the median nerve and allow the nerve and tendons to glide smoothly. Carpal tunnel release is an ambulatory procedure that is routinely performed under local anesthesia and is warranted in severe cases of CTS with muscle atrophy.37 The two types of carpal tunnel release are open repair and endoscopic repair.6 Open surgical repair utilizes a longitudinal skin incision approximately 4 to 5 cm long at the base of the hand to cut the transverse carpal ligament and palmar fascia.37 As with any surgery, risks of open carpal tunnel release include bleeding, infection, scar tenderness, loss of grip strength, and pillar pain; however, these complications occur in fewer than 3% of patients.37
Endoscopic carpal tunnel release involves the use of an endoscope and either a single or dual portal incision through which instruments are inserted to cut the transverse carpal ligament. This technique requires one or two smaller transverse incision(s) approximately 1.0 cm in length, which may shorten recovery time.6 The risks of endoscopic carpal tunnel release include paresthesia of the ulnar and median nerves, injury to the superficial palmar arch, reflex sympathetic dystrophy, and laceration of the flexor tendons. Complications occur in fewer than 2.67% of patients.38 A randomized prospective study that compared outcomes of patients who underwent endoscopic versus open carpal tunnel release reported no significant difference between the groups with regard to symptom amelioration, EMG results, and complications at the conclusion of the 6-month postoperative period.38
Researchers are studying the effects of progesterone in treating CTS by comparing outcomes in patients who receive local corticosteroid injection with those who receive a progesterone injection into the carpal tunnel. In addition to its role in the female reproductive cycle, progesterone is known for its neuroprotective properties, helping to promote the viability of neurons in the brain, spinal cord, and peripheral nervous system.39 Progesterone may promote myelination and neuroregeneration by reducing inflammation, swelling, and apoptosis, thereby increasing the survival of neurons.39 In addition to its anti-inflammatory effects, progesterone has been shown to reduce edema formation after traumatic brain injury, leading to the hypothesis that the hormone may act locally by reducing swelling and pain in the carpal tunnel.39 Research is still in progress, and no definitive suggestions have been made on the use of progesterone therapy.
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