Write a short note on carpal tunnel syndrome.

Definition & Anatomy

Carpal tunnel syndrome is a compressive (entrapment) neuropathy of the median nerve as it passes through the carpal tunnel at the wrist. It is the commonest entrapment neuropathy, affecting women three times more often than men, typically between 40 and 60 years.

The carpal tunnel is bounded by the carpal bones posteriorly and laterally and by the flexor retinaculum (transverse carpal ligament) anteriorly. It transmits ten structures: the median nerve, four tendons of flexor digitorum superficialis, four of flexor digitorum profundus, and the tendon of flexor pollicis longus. Because the tunnel is rigid, any increase in its contents or reduction in its dimensions compresses the most vulnerable structure — the median nerve.

Causes

Clinical Features

• Pain, tingling and numbness in the median nerve distribution — the thumb, index, middle and radial half of the ring finger.
• Characteristically worse at night, waking the patient, who obtains relief by shaking or hanging the hand over the edge of the bed (the "flick sign").
• Pain may radiate proximally to the forearm and even the shoulder, which misleads the unwary into diagnosing cervical radiculopathy.
• Clumsiness and weakness of grip, with difficulty buttoning clothes or holding small objects.
• Late signs: wasting of the thenar eminence (abductor pollicis brevis, opponens pollicis, flexor pollicis brevis) and weakness of thumb abduction and opposition.

Clinical Tests

Investigations

• Nerve conduction studies and electromyography — the confirmatory investigation, showing prolonged distal motor and sensory latency across the wrist with slowed conduction velocity; EMG shows denervation of abductor pollicis brevis in severe cases.
• Ultrasound or MRI of the wrist demonstrates nerve swelling proximal to the tunnel and identifies space-occupying lesions.
• Investigate the underlying cause: thyroid function tests, fasting glucose and HbA1c, rheumatoid factor, and growth hormone/IGF-1 if acromegaly is suspected.

Management

Conservative (mild to moderate disease):

• Neutral wrist splint worn at night — first-line and often sufficient.
• Activity modification and ergonomic correction of wrist posture.
• Treat the underlying cause — thyroxine in hypothyroidism, glycaemic control in diabetes. Pregnancy-related cases usually resolve spontaneously after delivery.
• NSAIDs for symptom relief; local corticosteroid injection into the carpal tunnel gives useful short- to medium-term relief.

Surgical (severe, persistent or with thenar wasting):

• Surgical decompression by division of the flexor retinaculum, performed open or endoscopically. Indicated for failure of conservative treatment, thenar wasting, or severe abnormality on nerve conduction studies. Results are good, though recovery of wasted muscle may be incomplete if surgery is delayed.