Carpal tunnel syndrome
Description
- Compression of the median nerve within the carpal tunnel, beneath the flexor retinaculum
- The commonest entrapment neuropathy - and the commonest cause of hand paraesthesia
- Contents of the tunnel: median nerve + 9 flexor tendons (4 FDS, 4 FDP, FPL) in a rigid osseofibrous space
- *The palmar cutaneous branch leaves the median nerve PROXIMAL to the tunnel -> the thenar eminence skin is spared*
- Sensory loss over the palm at the base of the thumb points to a lesion proximal to the wrist, not carpal tunnel syndrome
- Recurrent motor branch -> abductor pollicis brevis, opponens pollicis, flexor pollicis brevis (superficial head) and the first two lumbricals ("LOAF")
Epidemiology
- Prevalence ~3-5% of adults; incidence ~1-3 per 1,000/yr
- F>M ~3:1
- Peak 40-60 yrs (and a second peak in pregnancy)
- Bilateral in >50% - usually worse in the dominant hand
- Symptoms in ~20-60% of pregnancies, typically third trimester
Aetiopathogenesis
Causes and predispositions
- Idiopathic - the majority
- Repetitive occupational wrist flexion/extension, vibration exposure, forceful gripping
- Rheumatoid arthritis - tenosynovitis
- Hypothyroidism
- Acromegaly
- Pregnancy - fluid retention; usually resolves postpartum
- Gout and other crystal deposition
- Obesity
- Amyloidosis - dialysis-related beta-2 microglobulin, and ATTR (transthyretin)
- Diabetes mellitus - both a cause and a confounder (coexisting polyneuropathy)
- Carpal bone osteomyelitis, other space-occupying lesions (ganglion, lipoma, anomalous muscle), distal radius fracture/malunion
- Also: oral contraceptive, menopause, haemodialysis, sarcoidosis, mucopolysaccharidoses
- *Bilateral carpal tunnel syndrome in an older man, especially preceding cardiac symptoms by 5-10 years, should prompt consideration of ATTR amyloidosis* - it is treatable
Mechanism
- inc pressure within a non-compliant tunnel -> venous congestion -> epineural oedema -> ischaemia
- -> focal demyelination first (reversible; paraesthesia, slowed conduction), then axonal loss (irreversible; wasting, fixed sensory loss)
- Wrist flexion and extension both raise tunnel pressure -> nocturnal symptoms, because the wrist flexes in sleep
Diagnosis
Symptoms - the history does most of the work
- Numbness, tingling and burning in the median distribution - thumb, index, middle and radial half of the ring finger
- Nocturnal symptoms waking the patient, relieved by shaking or hanging the hand out of bed ("flick sign") - the most characteristic feature
- Aggravated by driving, holding a phone or a book, typing
- Pain may radiate proximally into the forearm and even the shoulder - this does not exclude the diagnosis
- Later: clumsiness, dropping objects, difficulty with buttons and keys
- Patients frequently describe the whole hand as numb - do not discard the diagnosis on that basis
Examination
- Thenar eminence wasting and surgical scars (previous release)
- Sensory loss over the lateral three-and-a-half fingers, with the thenar skin spared
- Weakness of thumb abduction, flexion and opposition - test abductor pollicis brevis (thumb pointing to the ceiling against resistance)
- Tinel sign - percussion over the volar wrist reproduces paraesthesia
- Phalen sign - sustained wrist flexion for >45-60 seconds reproduces symptoms
- Both are specific-ish but insensitive; a negative test does not exclude the diagnosis
- Durkan carpal compression test - direct pressure for 30 s; better sensitivity than Tinel or Phalen
- Examine for the underlying cause: acromegalic features, rheumatoid hands, thyroid status, diabetic complications, and take a pregnancy history
Clinical prediction
- CTS-6 clinical scoring tool - numbness in the median distribution, nocturnal numbness, thenar weakness/atrophy, Tinel, Phalen, loss of two-point discrimination
- *Now recommended as sufficient for diagnosis in most patients - it performs as well as ultrasound, nerve conduction studies and EMG*
Nerve conduction studies
- Not required to diagnose typical carpal tunnel syndrome - reserve for atypical presentations, suspected alternative or coexisting diagnosis, medicolegal cases, or before surgery where the diagnosis is uncertain
- Findings:
- Prolonged distal SENSORY latency across the wrist - the earliest and most sensitive abnormality
- Prolonged distal MOTOR latency to abductor pollicis brevis on median stimulation at the wrist
- Reduced conduction velocity across the wrist, with normal forearm conduction
- Severe disease: reduced CMAP/SNAP amplitude, denervation on needle EMG of APB
- *A normal study does not exclude carpal tunnel syndrome* - ~10-20% of clinically definite cases have normal studies
- *A Martin-Gruber (median-to-ulnar) anastomosis in the forearm can produce a normal proximal but prolonged distal latency* - a recognised source of confusion
Investigate for a cause
- TFT, HbA1c/fasting glucose, IGF-1 (acromegaly), beta-hCG (pregnancy)
- Consider RF/anti-CCP, urate, ESR/CRP
- Ultrasound - median nerve cross-sectional area at the tunnel inlet (>=10 mm2 abnormal); also identifies ganglia, tenosynovitis, anomalous muscles
- ATTR amyloid work-up if bilateral CTS in an older man with cardiac or autonomic features
Differential
- C6 radiculopathy (neck pain, Spurling positive, biceps/supinator reflex loss, weakness beyond the median distribution)
- Proximal median nerve entrapment (pronator syndrome) - palmar cutaneous branch involved, no nocturnal predominance
- Thoracic outlet syndrome, brachial plexopathy
- Peripheral polyneuropathy (diabetic), cervical myelopathy, syringomyelia
- Vibration white finger, Raynaud, complex regional pain syndrome
Management
A. Mild-to-moderate disease without motor deficit
- Neutral wrist splint worn at night - first-line, effective, low cost; 4-6 weeks before judging
- Activity and ergonomic modification; treat the underlying cause (thyroid, diabetes, rheumatoid, weight)
- Nerve and tendon gliding exercises, hand therapy
- NSAIDs, oral corticosteroids, diuretics, pyridoxine and ultrasound therapy have little or no durable benefit
B. Corticosteroid injection
- Local corticosteroid injection into the carpal tunnel gives good SHORT-TERM relief
- *Strong evidence that it does NOT provide long-term improvement*
- Useful as a bridge to surgery, as a diagnostic aid, or in pregnancy where surgery is best avoided - not as definitive treatment
C. Pregnancy
- Splinting and reassurance - most resolve within weeks to months postpartum
- Injection if severe; avoid surgery unless there is progressive motor loss
D. Surgical decompression - division of the flexor retinaculum
- Indications
- Thenar wasting or weakness (do not wait - axonal loss recovers poorly)
- Persistent symptoms despite adequate conservative treatment
- Severe symptoms or severe abnormality on nerve conduction studies from the outset
- Open, mini-open and endoscopic release give equivalent long-term outcomes
- Endoscopic offers faster early return to work; open is cheaper and has a lower risk of nerve injury
- Local anaesthetic alone is sufficient - no need for sedation or a tourniquet in most cases; office-based release is safe
- ~70-90% good-to-excellent outcomes; nocturnal symptoms usually resolve within days
- Complications: pillar pain, scar tenderness, incomplete release, recurrent motor branch or palmar cutaneous nerve injury, infection, CRPS, recurrence (~3-5%)
- Post-operative: early mobilisation, hand therapy; return to light duties ~2 weeks, heavy manual work ~4-8 weeks
Associations
- Hypothyroidism, acromegaly, diabetes mellitus, obesity
- Rheumatoid arthritis, gout and other crystal arthropathies, scleroderma
- Pregnancy and the puerperium; oral contraceptive; menopause
- Amyloidosis - dialysis-related (beta-2 microglobulin) and ATTR (hereditary and wild-type)
- Chronic kidney disease and haemodialysis (also arteriovenous fistula steal)
- Occupational: repetitive wrist flexion, forceful gripping, vibrating tools
- Other entrapments in the same patient - "double crush" with a cervical radiculopathy; hereditary neuropathy with liability to pressure palsies
- Trauma - distal radius fracture and malunion, lunate dislocation
- Mucopolysaccharidoses, sarcoidosis, tuberculosis of the flexor sheath
Natural history & complications
- Mild disease often fluctuates and up to a third improve spontaneously, especially pregnancy-related and recent-onset cases
- Untreated moderate-severe disease progresses: intermittent nocturnal paraesthesia -> constant numbness -> thenar wasting and permanent sensory loss
- Recovery after decompression is best predicted by the duration and severity of axonal loss
- Paraesthesia and night pain resolve quickly; established wasting and two-point discrimination loss may never recover**
- Recurrence after surgery ~3-5%; persistent symptoms are more often an incomplete release, a wrong diagnosis, or a coexisting cervical radiculopathy
Complications
- Permanent thenar wasting and loss of thumb opposition - impaired pinch grip, dropping objects
- Painless burns and injuries to insensate fingertips
- Chronic pain, sleep disruption, reduced work capacity
- Post-operative: pillar pain, scar hypersensitivity, nerve injury, CRPS
Monitor
- Thenar bulk and abductor pollicis brevis power at each review - the finding that converts management from conservative to surgical
- Symptom scores (Boston Carpal Tunnel Questionnaire), nocturnal symptom frequency
- Underlying condition control - thyroid, glucose, weight, inflammatory disease
- Occupational exposure and workplace modification
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