Carpal Tunnel Syndrome
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Direct answer
Night-time numbness in the thumb, index, middle and radial half of the ring finger, relieved by shaking the hand — the classic flick sign — identifies carpal tunnel syndrome, compression of the median nerve under the flexor retinaculum at the wrist. It is commonest in middle-aged and pregnant women, associates with hypothyroidism, diabetes, rheumatoid arthritis, acromegaly and occupations of repetitive vibration or forceful grip, and progresses from intermittent sensory symptoms to persistent numbness, thenar wasting, and weakness of thumb abduction. The LOAF muscles (lateral two lumbricals, opponens pollicis, abductor pollicis brevis, superficial flexor pollicis brevis) are the median-supplied victims, with abductor pollicis brevis wasting the visible endpoint; Phalen's wrist-flexion test and Tinel's percussion provoke the paraesthesia, and nerve conduction confirms with prolonged distal motor latency. Treatment climbs from neutral wrist night splints and corticosteroid injection to surgical division of the flexor retinaculum, which cures the overwhelming majority.
What you must remember
- Contents and boundaries: the tunnel carries the median nerve plus nine tendons (four FDS, four FDP, flexor pollicis longus); the nerve lies radially and superficially, and the palmar cutaneous branch leaves proximal to the tunnel — hence thenar skin is spared.
- LOAF motor deficit: lateral two lumbricals, opponens pollicis, abductor pollicis brevis, flexor pollicis brevis — test APB by resisted palmar abduction perpendicular to the palm; thenar gutter wasting is late.
- Provocation tests: Phalen — maximal wrist flexion for 60 seconds reproduces symptoms; Tinel — percussion over the tunnel; Durkan compression — direct pressure 30 seconds; none replaces nerve conduction.
- Electrophysiology: distal motor latency above about 4.2 ms to APB and slowed sensory conduction grade severity from mild (sensory only) to severe (absent responses, denervation).
- Associations: pregnancy (usually resolves post-partum), hypothyroidism, diabetes, rheumatoid tenosynovitis, acromegaly, dialysis amyloid — bilateral disease warrants thyroid and glucose screening.
- Treatment ladder: neutral night splint and activity modification; corticosteroid injection ulnar to the nerve (short-term benefit and a useful prognostic test); open or endoscopic release of the retinaculum under local anaesthesia — both with prompt relief.
Working through a typical presentation
A 48-year-old woman with type 2 diabetes wakes repeatedly at night with the right hand "asleep" — thumb, index and middle fingers burning — relieved only by hanging the arm and shaking it. Phalen is positive at 40 seconds, Tinel positive over the tunnel, two-point discrimination diminished over the radial three and a half digits but normal over the thenar eminence (the palmar cutaneous branch bypasses the tunnel — anatomical proof of compression within it), and early thenar flattening with weak palmar abduction is present. Neck and elbow examination are normal, excluding a proximal double crush.
Because both hands are symptomatic on direct questioning, thyroid function is checked alongside glycosylated haemoglobin. Nerve conduction confirms moderate CTS — sensory slowing with distal motor latency 5.1 ms — and excludes a dominant diabetic polyneuropathy, an essential distinction since diabetes produces both. She starts a neutral night splint; night symptoms improve but daytime numbness and weakness do not, so open release under local anaesthesia follows, dividing the retinaculum under vision while protecting the recurrent motor and palmar cutaneous branches. Night pain relief is typically immediate; sensory recovery precedes motor, and established thenar wasting recovers least — the reason surgery precedes wasting.
Where students slip
The first slip is including thenar skin in the sensory deficit — the palmar cutaneous branch arises proximal to the retinaculum, so its sparing is diagnostic gold. The second is motor anatomy: the recurrent motor branch arises just distal to the retinaculum and may be subligamentous or transligamentous, which is why release is done under vision. The third is treating every numb diabetic hand as neuropathy: bilateral symmetry, stocking distribution and absent ankle jerks point to polyneuropathy, while Phalen positivity, nocturnal predominance and LOAF weakness point to the tunnel — and the two coexist often enough that conduction studies are the tiebreaker. The pregnancy angle is a favourite: splints first, injection second, surgery deferred until after delivery.
Frequently asked questions
Why is thenar skin sensation spared in carpal tunnel syndrome?
The palmar cutaneous branch leaves the median nerve proximal to the flexor retinaculum and passes superficial to it, escaping compression within the tunnel.
Which muscles are affected and how is abductor pollicis brevis tested?
The LOAF group — lateral two lumbricals, opponens pollicis, abductor pollicis brevis, flexor pollicis brevis; APB by resisted palmar abduction of the extended thumb perpendicular to the palm.
What does Phalen's test involve?
Holding the wrists in complete flexion for up to 60 seconds; reproduction of paraesthesia in the median distribution is positive, the most sensitive bedside provocation.
When is surgery preferred over conservative treatment?
Persistent symptoms despite splinting and injection, moderate-to-severe conduction abnormality, thenar wasting or abductor weakness — release before wasting becomes permanent.
How does pregnancy-related carpal tunnel behave?
Fluid retention compresses the nerve, usually in the third trimester; night splints and postural measures first, steroid injection if disabling, with symptoms typically resolving after delivery.