November 29th, 2020
Pain and paresthesia
The pain of carpal tunnel syndrome is most commonly felt in the palmar surface of the thumb, index, and middle fingers. However, the whole hand can be affected. The pain can also radiate to the elbow or shoulder. This can often start off worse in the evenings and progress to affect the patient during the daytime as well.
The underlying cause is compression of the median nerve as it passes through the narrowed carpal tunnel.
Pain and paresthesia may improve when shaking the affected hand. This is thought to be due to transient relief of median nerve compression.
Loss of motor function
Adduction and opposition of the thumb can be affected. This leads to difficulty in grasping objects firmly and tasks requiring fine motor control (e.g., picking up a needle or buttoning a shirt). This is because injury to the median nerve leads to weakness and clumsiness of the hand.
Workplace exposure to activities requiring prolonged wrist flexion or extension, overuse of flexor muscles, or exposure to vibration is a risk factor for CTS. This type of exposure can be seen in manual workers employed in construction, logging, manufacturing, or certain service industries; and in artisans.
Extrinsic and intrinsic risk factors
Extrinsic risk factors include obesity, hypothyroidism, pregnancy, menopause, renal failure, oral contraceptive use, and congestive heart failure. These conditions affect the body's fluid regulation, and can increase the fluid volume within the carpal tunnel.
Intrinsic risk factors refer to tumors and similar pathologies that increase the pressure on the median nerve by taking up space within the carpal tunnel.
Tinel's percussion test
Tapping the median nerve over the flexor retinaculum will worsen symptoms. This is because percussion of an irritated nerve can elicit paresthesia along its distribution.
Note that the literature reports a wide range of values for the sensitivity and specificity (i.e., 48% to 73% and 30% to 94% respectively) for this test.
This is performed by having the patient flex their wrists by joining the dorsal aspects of their hands together for one minute, thus stretching the median nerve. Increased pain or paresthesia of the hand constitutes a positive result.
Carpal compression test
This is performed by applying firm pressure over the carpal tunnel for 30 seconds. The appearance of sensory symptoms indicates a positive compression test; and has a sensitivity and specificity of 64% and 83% respectively.
Signs of predisposing risk factors
There may be stigmata of medical conditions that predispose to CTS, e.g., obesity, acanthosis nigricans, myxedema, acromegaly, signs of pregnancy, etc.
Patients with severe CTS may demonstrate neurological deficits such as hypalgesia (decreased pain sensation), lack of two-point discrimination, thenar atrophy, and weakness of thumb adduction and opposition.
Hypalgesia can be appreciated by comparing pain sensation of palmar surface of the index finger with that of the little finger of the same hand. Lack of two-point discrimination manifests as inability to distinguish between two objects touching the skin <6 mm apart.
A wrist with an increased depth-to-width ratio has an odds ratio (OR) of 4.56 for CTS.
The reason for this association is unclear; it is postulated that a square-shaped carpal tunnel configuration predisposes to median nerve compression.
Pain and neurological deficits of the hand can occur in patients with cervical radiculopathy. Age-related degeneration of the cervical spine, a condition known as cervical spondylosis, is the most common cause. However, these patients often demonstrate symptoms proximal to the carpal tunnel, such as neck pain.
Diagnostic maneuvers include the Spurling test, shoulder abduction test, neck distraction test, and the Valsava maneuver. The Spurling test is considered positive if symptoms are reproduced by exerting the neck to extension, ipsilateral rotation, and downward pressure on top of the head.
Radiographs of the neck, MRI, and computerized tomography (CT) scan play an important role in the work up of suspected cervical radiculopathy.
Proximal median neuropathy
Examples are pronator teres syndrome (PTS) and anterior interosseous nerve (AIN) syndrome; these can present with signs and symptoms similar to carpal tunnel syndrome (CTS), such as pain and paresthesia of the hand, loss of grip, and positive Phalen's and Tinel's tests.
However, involvement of musculature proximal to the carpal tunnel is more suggestive of PTS. EMG and NCS can pinpoint where the median nerve entrapment occurs, thus distinguishing between PTS and CTS.
De Quervain tendinopathy
Sometimes referred to as "gamer's" or "mother's" thumb, de Quervain tendinopathy is a common condition that leads to hand pain and poor grip.
Unlike CTS, which is due to nerve entrapment, de Quervain's tendinopathy is caused by irritation of the abductor pollicis longus and the extensor pollicis muscles from thickening of the synovial sheath that encases them.
Patients present pain with Finkelstein's test but not the paresthesia seen in CTS.
Thoracic outlet syndrome
Thoracic outlet syndrome (TOS) can present with pain and paresthesia of the hand and arm, due to compression of nerves of the brachial plexus, and/or the subclavian blood vessels that traverse the opening between the first rib and the axilla. The vascular subset of this condition can produce painful swelling, chest pain, cyanosis, thromboembolic events, and potentially fatal ischemia.
Radiography, MRI, and CT can be used to distinguish between the different causes, which can be categorized as either soft-tissue or osseous abnormalities.
Peripheral neuropathy can manifest as paresthesia and sensory deficits of the hands. This can be secondary to a range of conditions such as diabetes mellitus, human immunodeficiency virus (HIV) infection, chemotherapy, vitamin deficiencies, and dysproteinemias.
A detailed history and physical exam will reveal clues as to the underlying cause. Depending on the suspected etiology, investigations that may be needed include complete blood counts, renal function tests, fasting blood glucose, hemoglobin A1c (HbA1c), thyroid stimulating hormone, vitamin b12 levels, and screening for HIV and Lyme disease.
Nerve conduction studies
Nerve conduction studies (NCS) are the gold standard for the diagnosis of carpal tunnel syndrome (CTS). An action potential is induced along the nerve to be studied. Then, electrodes located distally or proximally detect depolarizations and thus the rate and amplitude of nervous impulse conduction can be quantified.
Findings suggestive of CTS include decreased velocity of sensory and motor conduction and increased latency. Usually reserved for atypical cases when other diagnoses are considered.
Used to measure the cross-sectional area of the median nerve. A value greater than 9 mm^2 is highly suggestive of CTS. Other ultrasonographic findings include flattening of the median nerve as it passes the carpal tunnel and palmar bowing of the flexor retinaculum (PBFR).
Benefits include low-cost, patient comfort, and the ability to detect mass lesions, tenosynovitis, and other causes of wrist pain. Highly user dependent.
Magnetic resonance imaging (MRI)
Usually not indicated but is the best imaging modality for diagnosing rarer causes of CTS such as bone deformities, ganglions, or vascular tumors that may have significant impact on treatment strategy.
Findings suggestive of CTS include nerve swelling, increased signal intensity, and palmar bowing of the flexor retinaculum (PBFR). Usually preferred by patients over NCS, but very expensive.
Nerve conduction studies
Should be performed before surgery not only to confirm the diagnosis but to predict the outcomes. Patients with severe carpal tunnel syndrome (CTS) may have less benefit with surgery, but serial NCS showing improvement following non-surgical measures may provide reassurance and encouragement.
Magnetic resonance imaging (MRI)
Useful to predict surgical outcomes by measuring the length of the portion of the median nerve displaying an abnormal signal. Can be used following failed carpal tunnel surgery or to guide treatment when space-occupying lesions are suspected.
This includes avoiding or minimizing the use of vibrating tools, or objects requiring a prolonged, tight grip, for at least one month. Strategies include alternating task assignment, an increased number of breaks or taking sick leave.
May be offered to patients with mild or moderate carpal tunnel syndrome (CTS). Options include splinting, corticosteroid therapy, non-steroidal anti-inflammatory drugs (NSAIDs) physical therapy, yoga, vitamins B6 and B12 administration and therapeutic ultrasonography.
Short-term benefits are usually seen after two to six weeks. Lack of improvement after six weeks warrants consideration of an alternate approach. Other purported therapies involving the use of magnets or chiropractic treatment have failed to show a significant benefit.
Immobilizes the wrist joint to prevent extreme flexion and/or extension and reduce carpal tunnel pressure. Initial treatment for mild to moderate CTS. Simple, low cost, well tolerated and easily removable. Particularly useful in cases of CTS due to temporary or medically treatable causes such as pregnancy or hypothyroidism.
Improves symptoms on a short-term basis by inhibiting inflammation and edema. However, reduced collagen and proteoglycan synthesis may lead to diminished tenocyte function resulting in decreased tendon strength and degeneration. Furthermore, studies have failed to show long-term improvement with this therapy.
Carpal tunnel release (CTR)
Surgical referral should be made when symptoms are severe, progressive neurological deficit is present, or no improvement is seen after three months of conservative management. More effective than splinting, CTR consists of dividing the transverse carpal ligament (TCL) to relieve pressure on the median nerve. More than 70% of patients have long-term improvement.
Approaches include open CTR (OCTR) and endoscopic CTR (ECTR). OCTR is the most reliable approach and is indicated for the treatment of CTS due to any pathology, including refractory cases. Advantages of ECTR over OCTR include less scarring, less postoperative pillar pain and faster recovery. However, there is increased risk of iatrogenic nerve injury.