• Clinical science

Carpal tunnel syndrome

Abstract

Carpal tunnel syndrome (CTS) is a peripheral neuropathy caused by chronic or acute compression of the median nerve by the transverse carpal ligament. It is characterized by both sensory disturbances (pain, tingling, and numbness) and motor symptoms (weakness and clumsiness of the thumb) in the area innervated by the median nerve distal to the carpal tunnel. Several occupational and non-occupational risk factors (e.g., manual labor, age, sex, diabetes) have been associated with the syndrome. The presence of clinical symptoms and signs of CTS (e.g., the hand elevation test, carpal compression test, and Phalen's test) should raise suspicion, but diagnosis must be confirmed with specific neurological tests (e.g., EMG, ENG). Conservative management (i.e., immobilization with a splint, local steroid injections, and ultrasound therapy) may be effective in patients who only experience mild to moderate symptoms. Surgical release of the transverse carpal ligament with decompression of the median nerve is indicated in acute cases or patients with moderate to severe symptoms (atrophy of the thenar eminence).

Epidemiology

  • Most common entrapment neuropathy in the upper extremity (90% of all cases)
  • The prevalence and yearly incidence of CTS may change according to several occupational and non-occupational factors.

References:[1]

Epidemiological data refers to the US, unless otherwise specified.

Etiology

The following risk factors are associated with CTS:

References:[2][3][4][5]

Pathophysiology

The carpal tunnel is a narrow fibro-osseous structure at the level of the palmar aspect of the wrist, delimited by carpal bones on the bottom and on the sides, and by the transverse carpal ligament on the top. It contains flexor tendons and the median nerve. Any event or condition that increases the pressure within the carpal tunnel causes a compression of the structures within it:

  • Compression → impaired blood flow and altered microvascular structure of the median nerve → inflammatory reaction → edema and hypoxiaaxonal degeneration

References:[6][7]

Clinical features

Mild to moderate

  • Sensory symptoms on the palmar surface of the thumb, index, and middle finger; and radial half of the ring finger
    • Burning sensation/paresthesia
    • Loss of sensation/numbness
  • Symptoms worsen at night

The palmar surface of the thenar eminence is spared! The sensory innervation of this area is supplied by the superficial branch of the median nerve, which arises 5–7 cm proximal to the carpal tunnel and is therefore not compressed.

Moderate to severe

  • Motor symptoms
    • Weakened pinch and grip; : Patients often complain of dropping objects.
    • Rare: thenar atrophy with muscle flattening and impaired thumb opposition.

The "pope's blessing" (inability to flex the first three digits when making a fist) is not a symptom of CTS! It is only seen in proximal lesions of the median nerve!

References:[6][8]

Subtypes and variants

Diagnostics

  • Provocative tests: There is no agreement as to which provocative test should be used to support the diagnosis of CTS. Several authors suggest combining two or more provocative tests to improve the specificity of the diagnosis.
    • Hand elevation test; : The hand is held above the head of the patient for approx. two minutes. The test is considered positive if the symptoms of CTS (paresthesia and numbness) are reproduced. This test is easy to perform in a clinical setting and has higher sensitivity and specificity than all other tests.
    • Carpal compression test: or Durkan's test: By applying moderate compression with the finger directly over the proximal edge of the carpal tunnel, the examiner may elicit paresthesia in the median nerve distribution.
    • Phalen's test: The wrist is actively or passively held in full flexion. If occurrence or aggravation of paresthesia in the fingers innervated by the median nerve is perceived within one minute, the test is positive. This finding is considered highly specific (approx. 85%) for the diagnosis of CTS.
    • Tinel's sign: Percussion or tapping with the fingertips over the carpal tunnel leads to shooting pain and/or paresthesias in the fingers that are innervated by the median nerve.
  • Electrophysiological tests
    • Nerve conduction studies (NCS; confirmatory test): prolongation of the distal motor and sensory latency
    • Electromyogram
      • Pattern of neurogenic disorder: abnormal spontaneous activity
      • Decreased activity, potentials with large amplitude

There is strong evidence against the use of clinical signs alone to diagnose CTS because of their questionable sensitivity and specificity. Thus, electrodiagnostic studies (particularly NCS) are essential for diagnosis!References:[8][9][10][11]

Treatment

Mild to moderate symptoms

  • Conservative treatment
    • Immobilization of the wrist with a padded, volar splint worn during the night
    • Steroid injection (e.g., triamcinolone)
    • Short-term treatment with NSAIDs
    • Ultrasound therapy may be considered.

Moderate to severe symptoms (or no response to conservative treatment)

References:[12]

Complications

Recurrence of CTS is rare (0.5–3%).

References:[13]

We list the most important complications. The selection is not exhaustive.