Carpal tunnel syndrome

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76 Carpal tunnel syndrome

Instruction

Examine this patient’s hands.

Salient features

History

• Ask the patient about nocturnal pain (commonest cause of hand pain at night). Often the pain wakes up and shakes the hand to ameliorate symptoms: ‘wake and shake’.

• Pain, tingling, burning, numbness or some combination of these symptoms on the palmar aspect of the thumb, index finger, middle finger and radial half of the ring finger (no such symptoms affect the fifth finger even on detailed questioning).

• History of oral contraceptives, rheumatoid arthritis, myxoedema, acrogmegaly, chronic renal failure or sarcoidosis.

• Take a family history (abnormally small size of carpal tunnel runs in families).

Examination

• Wasting of the thenar eminence (Fig. 76.1A)

• Weakness of flexion, abduction and opposition of thumb

• Diminished sensation over lateral three and half fingers

• Ask the patient, ‘What do you actually do with your hand(s) when symptoms are at their worst?’ If the patient makes flicking movement of the wrist and hand, similar to that employed in shaking down a clinical thermometer (the ‘flick sign’), this had both a sensitivity and a specificity >90% in one study (J Neurol Neurosurg Psychiatry 1984;47:870–2).

Fig. 76.1 Carpal tunnel syndrome. (A) Distribution of pain and/or paraesthesias (shaded area) when the median nerve is compressed by swelling in the wrist (carpal tunnel). (B) Phalen’s test.

Proceed as follows:

• Look carefully for scar of previous surgery (hidden by the crease of the wrist).

• Percuss over the course of the median nerve in the forearm: patient may experience tingling (Tinel’s sign (Fig. 76.1A). The sensitivity of Tinel’s sign ranges from 25 to 60%, although its specificity is higher (67 to 87%).

• Ask the patient to hyperextend the wrist maximally for 1 min; this may bring on symptoms (dysaesthesia over the thumb and lateral two and half fingers): Phalen’s test (Fig. 76.1B).

• Tell the examiner that you would like to:

• examine for underlying causes such as myxoedema, acromegaly and rheumatoid arthritis

• look for cervical spondylosis, frozen shoulder and tennis elbow (these may be associated)

• look for a Cimino–Brescia fistula for haemodialysis (J Neurol Neurosurg Psychiatry 1997;40:511).

Diagnosis

This patient has median nerve involvement of the hand with Tinel’s sign (lesion) caused by carpal tunnel syndrome as a complication of chronic haemodialysis (aetiology). The patient has disabling tingling and pain at night (functional status).

Questions

How would you treat this condition?

• Diuretics, NSAIDs, steroids have been studied in small trials but were not efficacious

• Wrist splint in neutral posture rather than in extension (80% report that a wrist splint alleviates symptoms, usually within days). Splinting also reduces sensory latency, suggesting that it may alter the underlying course of carpal tunnel syndrome. Ultrasound treatment (BMJ 1998;316:731–5)

• Local steroid injection should be given proximal to the carpal tunnel (not into the tunnel because it may damage the nerve) (BMJ 1999;319:884–6)

• Surgical decompression

• Alternative therapies. Data are limited: acupuncture, yoga-based stretching, strengthening and relaxation (greater improvement in grip strength and reduction of pain than with splinting), chiropractic therapy (was as effective for pain as splints and medication).

Advanced-level questions

How would you confirm the diagnosis?

Nerve conduction studies: increased latency at the wrist on stimulation of the median nerve; the muscle action potential from abductor pollicis brevis is a valuable diagnostic sign. Rarely, the proximal latency may be normal with a prolonged distal latency caused by an anastomosis between the ulnar and median nerves in the forearm. Therefore, a negative test does not rule the syndrome out absolutely but calls it into question (J Neurol Neurosurg Psychiatry 1976;39:449).

Mention a few clinical diagnostic tests

• Wrist extension test: the patient is asked to extend the wrists for 1 min; this should produce numbness or tingling in the distribution of the median nerve.

• Phalen’s test: the patient is asked to keep both hands with the wrist in complete palmar flexion for 1 min; this produces numbness or tingling in the distribution of the median nerve (Fig. 76.1B). Sensitivity and specificity ranges widely from 40 to 80%.

• Tourniquet test: the symptoms are produced when the BP cuff is inflated above the systolic pressure.

• Pressure test: pressure placed where the median nerve leaves the carpal tunnel causes pain.

• Luthy’s sign: is regarded as positive if the skinfold between the thumb and index finger does not close tightly around a bottle or cup because of thumb abduction paresis.

• Durkan’s test: direct pressure over the carpal tunnel (the carpal compression test); this is more sensitive and specific than Tinel’s and Phalen’s signs.

(See Lancet 1990;335:393.)

Mention other entrapment neuropathies

• Meralgia paraesthetica: lateral cutaneous nerve of the thigh trapped under the inguinal ligament

• Elbow tunnel syndrome: ulnar nerve trapped in the cubital tunnel (p. 290)

• Common peroneal nerve trapped at the head of the fibula (p. 294)

• Morton’s metatarsalgia: trapped medial and lateral plantar nerves causing pain between third and fourth toes

• Tarsal tunnel syndrome: trapped posterior tibial nerve

• Suprascapular nerve trapped in the spinoglenoid notch

• Radial nerve trapped in the humeral groove

• Anterior interosseous nerve trapped between the heads of the pronator muscle.

Jules Tinel (1879–1952), a French neurologist, described it as the ‘sign of formication’ in his book on nerve wounds. He took an active part in the French resistance.

TG Morton (1835–1903), a US surgeon, described this syndrome in 1876.

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