David F. Jimenez and Thomas Loftus

Case Presentation

A 46-year-old, right-handed female presented with a 5-year history of bilateral hand pain, greater on the right than on the left. The patient described numbness, weakness, cold sensitivity, and swelling in both hands. She described pain in the hands that often woke her at night and would be relieved by shaking her hands. Additionally, the patient stated that the pain in the right hand (8/10 in severity by a visual analog score) would radiate proximally into the forearm. Physical examination revealed atrophy of the thenar eminence on the right side and also demonstrated positive Phalen and Tinel tests bilaterally. Electromyographic studies confirmed slowing of motor conduction velocities across the carpal tunnel and sensory conduction velocities consistent with carpal tunnel syndrome. Operative options were discussed with the patient, who chose to undergo endoscopic carpal tunnel release. Biportal endoscopic release of the right median nerve was performed without complications and, in the first postoperative visit 1 week later, the patient stated that the numbness and tingling had completely resolved and the pain had decreased significantly to a level of 1 to 2/10. Furthermore, she stated that the pain and paresthesias in her right hand no longer woke her up, as they had prior to surgery.

Diagnosis

Carpal tunnel syndrome

Anatomy

The median nerve originates from nerve roots of C6, 7, and 8, and T1. These nerve roots comprise the lateral and medial cords of the brachial plexus before forming the median nerve. The median nerve does not branch until it passes below the elbow, where in the forearm it innervates numerous wrist and digital flexors. In the hand, it supplies the “LOAF” muscles, which include the first and second lumbricales, the opponens pollicis, the abductor pollicis brevis, and the flexor pollicis brevis. The recurrent motor branch of the median nerve most commonly arises 3 cm distally to the distal wrist crease and supplies motor innervation to the abductor pollicis brevis, opponens pollicis, and superficial head of the flexor pollicis brevis. The palmar cutaneous branch of the median nerve exits the median nerve prior to its entry to the carpal tunnel and then travels alongside the median nerve superficial to the flexor retinaculum into the palm, where it divides into a medial and lateral branch supplying the skin overlying the thenar eminence. This branch typically originates ˜2 cm proximal to the upper border of the flexor retinaculum but may have a variable origin and course. The sensory supply of the median nerve is to the radial 3½ digits of the hand via the common palmar digital branches of the median nerve.

The floor of the carpal tunnel is composed of the volar radiocarpal ligament and the ligamentous extensions between the carpal bones. The transverse carpal ligament, which extends over the concave surface of the carpal bones, forms the roof of the carpal tunnel. The transverse carpal ligament extends radially from the tuberosity of the scaphoid and the crest of the trapezium to its ulnar attachments, which include the hook of the hamate and the pisiform bone. Proximally, the transverse carpal ligament blends with the fibers of the antebrachial fascia at the distal wrist crease and extends ˜3 cm into the palm, near Kaplan’s cardinal line. The median nerve is located radial to the palmaris longus tendon and lies superficially beneath the transverse carpal ligament on the radial side of the tunnel. The superficialis and profundus flexor tendons lie deep within the carpal tunnel. The recurrent motor branch of the median nerve has a variety of branching patterns but the most common is the extraligamentous and recurrent type. In any branching pattern, the motor branch extends radially into the thenar muscles, which it innervates.

Characteristic Clinical Presentation

Differential Diagnosis

Although carpal tunnel syndrome describes a classical set of symptoms and physical examination findings, it may be confused with other neurological disorders. Sensory findings along the C6 and C7 distribution may resemble a compressive radiculopathy of the C6–7 nerve roots. Patients with bilateral hand numbness and weakness (or clumsiness) should have a careful neurological examination to rule out intrinsic cervical spinal cord pathology or extrinsic compression (cervical spondylitic myelopathy). Inflammatory conditions such as arthritis in the joints, tendonitis, and fasciitis also need to be considered. Proximal forearm nerve entrapment involving the median nerve can also mimic carpal tunnel syndrome. Physical findings of muscle atrophy in the palm can certainly be mimicked by multiple neuropathies or myopathies and necessitate thorough bilateral extremities evaluation. Clinical entities that have been associated with median nerve compressive entrapment neuropathy at the wrist include pregnancy, acromegaly, diabetes, rheumatoid arthritis, hyperthyroidism, amyloidosis, gout, and alcoholism. A variety of anatomical anomalies such as ectopic muscles, vascular tumors, and ganglion cysts have been reported. The clinician must rule out cervical root compression or thoracic outlet syndrome as possible etiologies for pain in the wrist and forearm. When performing the physical examination, the examiner should be looking for symmetrical versus asymmetrical findings, involvement of other muscles, and other associated findings not following the median nerve distribution. Given that carpal tunnel syndrome is often work related in etiology, secondary gain and psychogenic issues must also be considered in all patients.

Diagnostic Tests

A variety of studies have been performed in an attempt to predict the most useful and sensitive physical and diagnostic studies for diagnosing carpal tunnel syndrome. Although the use of nerve conduction abnormalities as a gold standard in the studies of carpal tunnel syndrome evaluation remains controversial, it is quite often used in an attempt to quantify the effectiveness of the physical examination. The Tinel sign is an examination that involves lightly tapping on the median nerve of the wrist from proximal to distal, in an attempt to reproduce tingling in the median nerve distribution. The Phalen test involves forced flexion of the wrist in an attempt to produce the paresthesias in response to this wrist position. The Durkan or carpal compression test involves the examiner pressing the carpal tunnel with his or her thumbs in an attempt to reproduce paresthesias in response to pressure within 30 seconds. Some studies have shown that the Durkan test was the most sensitive by producing positive findings in 89% of patients with electrodiagnostically proven carpal tunnel syndrome. The Phalen test and Tinel sign have sensitivity of 60% and 49%, respectively, and specificities of 80% and 55%, respectively. As stated earlier, sensory changes and weakness along the distribution of the median nerve–innervated areas are also an important part of the examination.

Although the sensitivity and specificity of electrodiagnostic studies are often used as a gold standard by which other parts of history and examination are compared, there is much disagreement about how reliable these examinations are. Many studies quote their sensitivity as high as 90% or greater, whereas others argue that the sensitivities range from 49 to 84%. In any case, motor latency across the carpal tunnel of greater than 4 msec is considered diagnostic of carpal tunnel syndrome. Distal motor latencies, motor conduction velocities, and compound muscle action potential amplitudes are all variables that can be measured. Furthermore, sensory conduction velocities can be assessed as well as sensory nerve action potentials. The American Academy of Electrodiagnostic Medicine considers any variation in the measurements of greater than 2 standard deviations above or below the mean of controls to be abnormal.

Management Options