Carpal Tunnel Syndrome (CTS)

Carpal Tunnel Syndrome (CTS)

Background:

The syndrome related to median nerve compression ("entrapment") at the wrist

- the nerve is compressed within the carpal tunnel as it passes below the flexor retinaculum (aka. transverse carpal ligament [TCL]) - along with the 9 flexor tendons

- closed space within which pressure may rise

- nerve dysfunction (incl. segmental demyelination and eventually axonal degeneration) occurs due to chronic mechanical compression

The most common entraptment mononeuropathy

- first described by Paget in 1865

- prevalence approx 125 per 100,000 (more common in women)

- up to 5% lifetime risk for developing CTS

- often bilateral but dominant hand more severely affected in most cases

Median Nerve:

- formed from divisions of both lateral and medial cords (C6 to T1)

- sends sensory fibres to digits 1-3 and motor fibres to some proximal forearm muscles (lateral cord)

- sensory fibres to digit 4 and muscles of distal forearm and hand via medial cord

- lies adjacent to brachial artery in antecubital fossa

- passes between two heads of pronator teres in forearm

- branches to pronator teres, flexor carpi radialis, flexor digitorum sublimis & palmaris longus

- gives off anterior interosseous nerve which innervates pronator quadratus, flexor pollicis longus (FPL) & flexor digitorum profundus (to digits 2-3)

- proximal to wrist , palmar cutaneous branch arises, running subcutaneously (and NOT within the carpal tunnel) supplying sensation to thenar eminence

- then enters wrist through carpal tunnel (bounded by carpal bones on three sides and roof formed by TCL)

- in the hand, muscular branches to Abductor pollicis brevis ('purest' median-innervated hand muscle), opponens pollicis, flexor pollicis brevis (superficial head) & first / second lumbricals

- sensory fibres distal to carpal tunnel innervate medial thumb, second & third digits & lateral half of fourth digit (volar as well as dorsal aspect distally beyond DIP joint)

Causes:

most commonly "idiopathic" - due to a nonspecific tenosynovitis of the TCL leading to raised compartmental pressure

- this may related to occupational / work-related changes (CTS is one of the most frequent causes of disability) but inconclusive evidence linking CTS to typing / computer use

- secondary causes include infiltrative disorders (amyloidosis), rheumatoid arthritis, diabetes mellitus, acromegaly, hypothyroidism, pregnancy (latter two with tissue edema) & fractures

- mass lesions in that region can also cause (ganglion, osteophyte, lipoma, anomalous muscle, aneurysm / persistent median artery, neurofibroma / schwannoma, hemangioma)

- hypothesis that in some related to congenitally small carpal tunnel

- can also occur in those susceptible to nerve injury (esp. HNPP = hereditary neuropathy with predisposition to pressure palsies)

Symptoms:

1. Intermittent pain, numbness or paresthesias in fingers (90%+)

- acroparesthesias

- often initially nocturnal, waking patient from sleep (ask if patient shakes the hand to resolve symptoms = Flick sign)

- pain may radiate up the arm to the elbow or even above (to shoulder, but no neck pain)

- may be provoked by hyperextension or hyperflexion of the wrist

- if asked, may localize the tingling to the index & middle fingers predominantly (sparing fifth)

- rarely note tingling in ulnar innervated digits as intact sensation felt here while rest numb!

- localization-based history not accurate in many as often describe numbness in whole hand

2. Subjective weakness of hand grip

- unusual to develop significant functional impairment in use of the hand except if severe

- motor-onset CTS is uncommon if it ever occurs so suspect C8/T1 radiculopathy or focal onset motor neuron disease

3. Subjective hand swelling and stiffness

4. Wrist pain

Signs:

1. Sensory disturbance

- ideally localized to 1st 3 fingers (distal median nerve distribution - sparing palmar branch)

- compare quality / intensity of pinprick to contralateral side or to ulnar innervated fifth digit

- two-point discrimination may be more sensitive test in early stages

2. Motor weakness

- best tested in APB (abductor pollicis brevis) by asking patient to abduct thumb (away from plane of the palm) against resistance

- likely to be normal in mild-moderate cases (and difficult muscle to test in isolation)

3. Thenar atrophy

- only if motor amplitudes reduced (not in early cases)

- ddx thoracic outlet syndrome, recurrent motor branch (of median n.) neuropathy, T1 radiculopathy, motor neuron disease / brachial plexus lesions

- can also be seen as a result of disuse atrophy with arthritis of the wrist / hand without any nerve abnormality

4. Tinel's sign:

- positive only if reproduce paresthesias in fingers by tapping lightly over distal wrist crease

- insensitive test with moderate specificity (56% sensitive, 80% specific - Positive LR 2.8)

- reverse Tinel's sign w/ paresthesias radiating retrodgrade up forearm may be more specific

5. Phalen's sign:

- ask to hold both wrists in hyper-flexion for 30-60 seconds to see if reproduce paresthesias

- insensitive test

6. Direct Compression:

- sustained pressure (eg. with thumb) over median nerve at wrist may reproduce symptoms

Differential Diagnosis: (esp of acroparesthesias)

1. Cervical radiculopathy (esp C6 for digits I and II, C7 for digits II and III)

- sometimes (not always) associated with neck pain

- scapular pain may indicate C7 radiculopathy

- pain or tingling may radiate from neck down arm into hand

- sensory loss proximal to wrist not seen in CTS

- worsened by coughing or sneezing and neck movements

- more often daytime (vs nocturnal in CTS)

- look for loss of biceps (C6) or triceps (C7) tendon reflex

- some hypothesize double-crush syndrome with proximal nerve root compression worsening distal entrapment by impairing axonal transport (not proven)

2. Ulnar neuropathy

- maximal sensory disturbance in ulnar distribution (ie. medial hand, fifth digit predominantly)

- worsened by leaning on elbow and/or positive Tinel's sign (with tapping over cubital tunnel)

3. Proximal median neuropathy:

- uncommon

- other muscles typically affected (eg. pronator syndrome with weakness of pronation, finger flexion & wrist flexion)

- in anterior interosseous syndrome no sensory involvement (weakness of FDP & FPL so unable to make "OK" sign with finger and thumb)

4. Distal Polyneuropathy

- sensory symptoms in both hands (all fingers) and usually (if length-dependent) similar paresthesias in lower limbs also

- most commonly in diabetic neuropathy

5. Upper Trunk Brachial Plexopathy

6. Neurogenic Thoracic Oulet Syndrome:

- sensory symptoms usually in ulnar distribution (fifth digit predominantly) while motor manifestations in median distribution (eg. thenar atrophy)

- pain localized to neck or shoulder region also

- uncommon to find this syndrome

7 High Cervical Lesion

- pseudo-CTS can sometimes occur with a lesion below the cervicomedullary junction

- causes include cervical spondylitic change, extramedullary tumors

8. Non-Neurological causes of wrist / hand pain:

- Tenosynovitis of APL / EPB tendons

- Trigger finger

- Osteoarthritis involving the thumb and/or wrist

- Raynaud's disease

Electrophysiological Testing:

Nerve Conduction Studies

- CTS is the most frequent reason for referral to most electrodiagnostic laboratories

- many tests and comparisons proposed as accurate diagnostic tests

- basic concept of most is to demonstrate slowing of conduction in either median motor or sensory fibres at the wrist

- best to demand two separate tests showing median nerve dysfunction at the wrist (MNW) as some normal people will have one abnormal test (standard deviation in population)

NB: may be poor correlation b/w symptoms and degree of abnormality on testing (except if objective sensory loss and muscle weakness with thenar atrophy)

- clinical diagnosis remains the gold standard > remains a small population of patients with clinically apparent CTS without any electrophysiologic abnormalities (may have symptoms from increased pressure and nerve ischemia without any demyelination or axonal loss)

NB: need to rule-out other causes of hand numbness (see DDx above)

Sensory studies

1. Comparison of median & ulnar sensory conduction between wrist and digit 4

- abnormal if median (over same distance) is slower by 0.4 sec

- sensitivity of 85% and specificity of 98%

2. Comparison of sensory actional potentials (SNAPs) to median innervated digits to those from ulnar and radial nerve

- if median smaller amplitude than either (esp radial which is usually lowest)

- comparison also of median vs ulnar/radial conduction velocities (slowing through tunnel)

Motor studies:

1. Median distal motor latency

- stimulate median nerve at wrist and recording from APB over 7cm distance

(this information for LHSC EMG lab as diff labs have diff techniques - so normative data varies)

- delay to > 4.3 msec (insensitive as motor fibres may be relatively spared)

2. Median motor amplitude (to thenar eminence)

- reduction in amplitude seen only late in disease (when thenar atrophy visible)

- seen in association with very prolonged distal latency (usually > 6 msec) and very low or absent sensory responses

NB: in the presence of a Martin-Gruber anastomosis (median to ulnar crossover in forearm) will see higher median CMAP at elbow compared to wrist (confirming anastomosis and fibre redirection) but also initial positive deflection with elbow stimulation (resulting from innervation of some thenar muscles by crossover fibres not slowed in carpal tunnel, with opposite dipole)

Needle EMG:

- usually not necessary in clinically likely CTS with clear nerve conduction abnormalities

- useful to demonstrate some axonal continuity in very severe CTS and exclude DDx

eg. may look for signs of denervation in APB not found in other median innervated muscles (eg FPL) or other C8/T1 muscles (EPB, EPL, EDC, FDI, ADM) to rule-out proximal disease

Grading Severity:

Borderline: prolonged sensory latency to IVth digit from median supply (vs ulnar)

Mild: sensory conduction velocity slowing without evidence of axon loss (normal SNAP ampl)

Mild-Moderate: slowing with mildly reduced SNAP amplitudes and mildly prolonged median motor terminal latency to thenar eminence

Moderate: slowing with moderate sensory / motor axonal loss (moderate reduction in SNAP or CMAP amplitudes, or moderate chronic partial denervation / reinnervation)

Severe: medial SNAP unobtainable or severe reduction in median CMAP amplitude with active denervation or severe chronic de-/reinnervation

Natural History:

Some cases may remit spontaneously (especially if short duration of symptoms)

- esp with avoidance of activities / postures that exacerbate symptoms (up to 30%)

- even more severe cases with functional impairment found to remit

Management:

1. Conservative / Non-invasive:

- observation appropriate if signs and/or functional impairment not severe

- may be successful in 50% or more (but recurrence may occur)

- Rest / reduced use of the affected arm (modified activities)

- Anti-inflammatory drugs: NSAIDs, possibly oral steroids (no evidence)

- Splinting of the wrist at night

- Diuretics (no evidence)

- No evidence for acupuncture, massage, chiropractic manipulation, snake oil

2. Invasive: usually reserved for non-responders to conservative / non-invasive Rx

- Steroid injections = short-term benefit (weeks usually)

- Surgery (see #3)

3. Carpal Tunnel Release:

- open surgical / endoscopic division of the TCL

- improvement rates of 80-90%

- may require few weeks off work (less for endoscopic procedure but higher rate of complications); complications incl. damage to thenar motor branch or palmar cutaneous branch (painful neuroma)

If patient does not improve or recurs suspect:

- inadequate release of TCL

- injury to median nerve or recurrent branch to thenar eminence at time of surgery

- recurrent compression due to scar formation

- wrong diagnosis (see Differential Diagnosis) - esp if NCS not done pre-op

References:

Campbell WW. Diagnosis and management of common compression and entrapment neuropathies. Neurological Clinics 1997; 15(3) 549-66.

D'Arcy CA, McGee S. Does this patient have carpal tunnel syndrome? JAMA 2000; 283: 3110-7.

Jablecki CM, Andary MT, et al. Practice parameter: Electrodiagnostic studies in carpal tunnel syndrome. Neurology 2002; 58: 1589-92.

Last update: February 2004

Reviewed by: Dr. M. W. Nicolle

Neurological Medicine Pocketbook

http://www.uwo.ca/cns/resident

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