Carpal tunnel syndrome is the most common compression neuropathy that occurs in the upper extremity with an estimated incidence of 1 to 3 cases per 1000 and a prevalence of 50 cases per 1000.⁷,⁸,⁹ The syndrome presents with paresthesia and numbness along the median nerve distribution to the radial three and a half digits. These symptoms typically begin at night, which may be the most sensitive predictor.¹⁰ The symptoms can occur during the day as the syndrome progresses and becomes more severe. Shaking of the hand, often referred to as the “flick sign,” may relieve symptoms. This sign is reported to have a sensitivity of 37% and specificity of 74%.⁸ Weakness of thumb palmar abduction and thenar eminence atrophy may appear later in the clinical course as the syndrome progresses.⁸

The median nerve takes origin from the C5 to T1 nerve roots and arises from the medial and lateral cords of the brachial plexus.¹¹ After traversing the upper extremity, the nerve ultimately passes into the wrist through the carpal tunnel, which begins at the volar wrist crease. The scaphoid tubercle and trapezium create the radial border, whereas the triquetrum, pisiform, and hook of hamate form the ulnar border. The dorsal floor is formed by the scaphoid, capitate, hamate, and triquetrum. Soft tissue structures create the volar border, consisting of the flexor retinaculum or transverse carpal ligament.⁹,¹¹ The median nerve is accompanied by the four tendons of the flexor digitorum superficialis, the four tendons of the flexor digitorum profundus, and the tendon of the flexor pollicis longus through the carpal tunnel.⁹,¹¹

Carpal tunnel syndrome occurs as a result of decreased space and increased pressure within the confined space of the cubital tunnel, which may result from tendon inflammation, edema, hormonal changes, or manual activity.¹² As a result, several risk factors have been associated with carpal tunnel syndrome, which include hypothyroidism, menopause, diabetes mellitus, obesity, arthritis, and pregnancy.¹² The increase in compartment pressure leads to decreased perfusion to the median nerve’s epineurium, leading to local tissue edema, decreased myelination, and ultimately reduced signal transmission due to axonal transport dysfunction.⁹,¹³ Venous return may also be compromised, leading to venous stasis and extraneural edema, whereas intraneural edema may occur chronically owing to the development of nerve fibrosis and scarring.¹³ Symptoms may occur during positions that reduce the size
of the carpal tunnel, such as wrist flexion or extension, which is why a wrist brace often helps. Carpal tunnel syndrome may also occur acutely, typically described following a distal radius fracture, carpal fracture/dislocation, and metacarpal fractures.⁹ Acute fractures resulting in carpal tunnel syndrome are especially important to consider in patients with MS, as these patients have a 25% overall lower prevalence of bone mineral density and their risk of fracture may be increased because of corticosteroid therapy.⁴

The clinical history and examination are critical in the diagnosis of carpal tunnel syndrome. History focuses on acuity, aggravating factors, associated activities, and relevant past medical history, as patients with MS may adjust their activities to compensate for their upper extremity disabilies.² Several physical examination maneuvers are used to aid in the diagnosis of carpal tunnel syndrome. The first is Phalen sign, which is performed by holding the wrist in prolonged flexion. This position causes compression of the carpal tunnel, and the sign is positive after several minutes if the patient’s symptoms are replicated. Phalen sign has a reported sensitivity between 42% and 85% and specificity of 54% to 98%.¹² Tinel sign, with a sensitivity of 38% to 100% and specificity of 55% to 100%, involves the replication of symptoms when the examiner repeatedly taps the patient’s carpal tunnel.⁸ Conducting a thorough sensory examination of the entire median nerve distribution with a comparison with the contralateral side is vital in patients with MS. Bertoni et al¹ reported decreased unilateral thumb sensation in 22% of patients with MS examined, and 68% of patients had decreased sensation bilaterally as measured by the Semmes-Weinstein monofilament test. Therefore, a patient with a unilateral sensory deficit affecting the index, long, and radial half of the ring finger may be due to carpal tunnel syndrome.¹⁴ In addition, other etiologies such as cervical radiculopathy or cervical myelopathy should be considered. Cervical radiculopathy results from compression of a spinal nerve root that typically results in unilateral pain and paresthesias that follow a dermatomal distribution as illustrated in Figure 24.1.¹⁵,¹⁶ In contrast, cervical myelopathy results from central spinal cord compression and the presentation may mimic that of MS with upper motor neuron symptoms, such as nondermatomal sensory disturbances, loss of balance, loss of coordination and difficulty with performing fine motor tasks, hyperreflexia, and weakness.¹⁶ A patient with cervical radiculopathy may reveal decreased neck range of motion, and symptoms may be replicated or relieved with a variety of examination maneuvers. The Spurling test is performed by axially loading the neck and then rotating and extending it toward the affected side. This maneuver was found to be the most sensitive and specific physical examination test for cervical radiculopathy with a sensitivity between 30% and 100% and a specificity of 75% to 100%.¹⁵,¹⁶ The shoulder abduction test, with a reported sensitivity between 17% and
78% and specificity of 75% to 92%, is another examination maneuver used, in which the patient’s symptoms are relieved when the shoulder is abducted and externally rotated.¹⁵ Lastly, the Valsalva maneuver may also elicit symptoms of cervical radiculopathy with a reported sensitivity of 22% and specificity of 94%.¹⁵,¹⁶ If cervical radiculopathy or myelopathy is suspected, computed tomography (CT) and magnetic resonance imaging are used to evaluate for cervical spondylosis or spinal cord compression with appropriate referral to a spine surgeon.

In addition to the above-mentioned physical examination findings or in cases of an uncertain diagnosis or equivocal examination findings, further testing may be required, such as nerve conduction studies, electromyography, or ultrasonography. Nerve conduction studies are advantageous because they can measure the severity of nerve degeneration, such as the amount of demyelination and axonal loss, which is important for future outcome.¹² Changes in conduction velocity are often detected first in sensory fibers before motor fibers.¹² Recently, ultrasound has been used and compared with electrophysiological assessments for the diagnosis of carpal tunnel syndrome to identify compression of the median nerve by assessing the cross-sectional area of the nerve before and after it is compressed. Ultrasonography has been reported to have a sensitivity of 77.6% and specificity of 86.8% compared with clinical diagnosis.¹²

Management of carpal tunnel syndrome includes both nonoperative and operative approaches. The goal of management is to reduce compression within the carpal tunnel. A trial of nonoperative management is warranted before opting for surgery. The patient should be counseled on avoiding provocative wrist motions and reducing heavy lifting.¹² Options include nonsteroidal anti-inflammatory drugs (NSAIDs), corticosteroid injections, and nighttime bracing. When bracing the patient with MS, careful follow-up is needed for repeat skin examinations, as these patients are prone to developing pressure sores.⁴ If symptoms do not resolve following initial nonsurgical treatment, a second nonsurgical modality can be trialed.¹⁷ If nonoperative management fails to address symptoms, surgical management is indicated and involves transection of the entire flexor retinaculum above the carpal tunnel, which may be performed using open, minimally invasive, or endoscopic techniques, all with high degrees of success. There is no difference in long-term outcome between each technique.¹² Potential complications that may result from carpal tunnel release include the injury to surrounding neurovascular structures and tendons, development of complex regional pain syndrome, scar tenderness, neuropraxia, and revision surgery. Patients with MS-attributed weakness, spasms, and sensory loss not associated with carpal tunnel may have worsening of their symptoms following surgery.⁴