Carpal Tunnel Syndrome

Introduction

• Carpal Tunnel Syndrome occurs when median nerve gets squished in the wrist causing pain, numbness, tingling and in more severe cases, weakness and clumsiness of the hands
• Most common compressive neuropathy in the upper extremity

Anatomy

• The median nerve arises from the C6,C7,C8 and T1 segments of the spinal cord
• Roots  from C6 and C7 provide sensory fibers which transmit sensation from the radial 3.5 fingers  (i.e. thumb to medial ½ ring finger)
• Roots from C8 and T1 provide motor fibers which supply muscles in the
  • Forearm
    • Pronator teres
    • Flexor carpi radialis
    • Palmaris longus
    • Flexor digitorum superficialis
    • Pronator quadrates
  • Hand
    • Abductor pollicis brevis
    • Flexor pollicis brevis
    • Opponens pollicis
    • 1st and 2nd lumbricals
• As it enters the wrist, the median nerve passes through the carpal tunnel a space enclosed by the transverse carpal ligament on the palmar side and carpal bones on the other 3 sides
• Median nerve shares this tunnel with 9 flexor tendons
• The carpal tunnel is smaller in diameter compared to males

Pathogenesis

• Inflammation or thickening of flexor tendons can result in increased pressure in the carpal tunnel
• Studies investigating the compression of human nerves show
  • Swelling and thickening of vessel walls in the endoneurium and perineurium
  • Vascular proliferation
  • Thinning of the myelin
  • Nerve fiber degeneration and regeneration
• Damage to the myelin or vessels supplying the nerve cause
  • Decreased conduction velocity
  • Possibly, axonal loss
• As a result, signals transmitted by the median nerve would be slowed or eventually
• Sensory fibers seem to be more sensitive to compression than motor fibers perhaps explaining why sensory findings often precede motor findings in CTS
• Early in the disease
  • There is no structural changes in the nerve
  • Neurologic symptoms are
    • Reversible
    • Intermittent
• Prolonged episodes of increased pressure in the carpal tunnel can lead to
  • Segmental demyelination of the nerve
  • Increased frequency
  • Increased severity of symptoms
• Prolonged ischemia can result in axonal injury and potentially irreversible nerve dysfunction
• Macroscopically, surgical reports describe an "hourglass" shaped deformity of the median nerve in the carpal tunnel which may reflect thinning of the nerve under the transverse carpal ligament and/or swelling of the nerve distal or proximal to transverse carpal ligament

Risk factors

• Associated with
  • Aromatase inhibitor use
  • Obesity
  • Pregnancy; due to fluid accumulation
  • Diabetes
  • Rheumatoid arthritis
  • Hypothyroidism
  • Amyloidosis
  • Connective tissue disease
  • Median mononeuropathy
  • Acromegaly; due to tendon sheath enlargement
  • Trauma to wrist
• It is not caused by work, any more than running after the bus causes heart disease
• Occupation may precipitate symptoms in patients with underlying disease
  • Prolonged use of hand-held vibratory tools
  • Repetitious flexion and extension of the wrist with forceful gripping
  • There is little/no evidence to support a relationship with keyboarding

Prevention

• Studies suggest splinting may alter the underlying course of CTS

Nutritional factors

• AAOS gudelines state that there is insufficient evidence to recommend for or against nutritional supplements or specific supplementation with vitamin B6 as treatment for carpal tunnel syndrome

Natural History

• Incidence : 1-3 cases per 1000 people per year
• Prevalence : 50 cases per 1000 people in the general population
• Male : Female 1:8
  • Bilateral involvement is common in females
  • More common in menopausal women
• Usually 40 - 50 years old
• Younger patients usually have associated factors

Clinical Presentation

• Symptoms usually include burning, numbness or tingling on the palmar side of the thumb, index finger, middle finger and radial half of ring finger sparing the little finger
• Symptoms amy relieve by hanging the arm at the side of the bed or walking around
• Pain may radiate up the arm
• "Classic symptoms" in sensory distribution of the median nerve have
  • 61% sensitivity
  • 71% specificity
• Patients often report worsening of symptoms at night. Nocturnal symptoms have
  • 51-77% sensitivity
  • 27-68% specificity
• Loss of two point discrimination in fingers supplied by the median nerve occurs in later stages of disease and has low sensitivity and high specificity
• Provacative tests
  • Tinel's sign: elicit by taping just proximal to the site of impingement
  • Phalen's test: hands flexed at wrist (consider negative if no symptoms after one minute)
  • Modified Phalen's test: hold pressure over carpal tunnel while flexing the wrists (consider negative if no symptoms after one minute)
  • Reverse Phalen's test: Extending wrists in a prayer-like position (consider negative if no symptoms after one minute)
  • Durkan's test: Hold pressure over carpal tunnel
    • Consider negative if no symptoms after one minute
    • Low sensitivity and specificity (36% and 57%, respectively)

Diagnositc criteria

• Numbness and tingling in the median nerve distribution
• Nocturnal numbness
• Weakness and/or atrophy of the thenar muscles
• Tinel sign
• Phalen's test
• Loss of 2-point discrimination

Late presentation

Denervation of the muscles of the hand supplied by the median nerve causes

• Decreased grip strength
• Decreased strength in opposition of the thumb resulting from

Differential Diagnosis

• More Proximal Lesion of Median Nerve
  • Can be caused by dislocation of ulna
  • Findings in hand would be similar
  • Distinctive features : weakness of muscles of the forearm supplied by median nerve
• Radiculopathy
  • C6 or C7 radiculopathy could look similar with similar findings in the hand
  • Distinctive features
    • Neck pain
    • Muscle weakness and sensory findings proximal to the carpal tunnel
• Ulnar neuropathy
  • Has similar description of numbness and tingling in the fingers
  • Distinctive features : patients would describe funny feelings in the little finger and ulnar side of the ring finger
• Pronator teres syndrome
• Hereditary neuropathy
• AIN syndrome

Psychosocial impact of disease

• The psychosocial impact of the disease depends on the
  • Patient's occupation
  • Lifestyle
  • Disease severity
• Decreased grip strength and increased clumsiness and frequency of dropped objects can be a significant source of impairment for people accustomed to working with their hands

Imaging and Diagnostic Studies

Carpal tunnel syndrome is a clinical diagnosis

X-Ray

• Can be used to rule out possible causes of increased pressure within the carpal tunnel such as fracture to the carpal bones or distal radius
• Imaging studies are not routinely used to evaluate CTS

Ultrasound

• Ultrasound has shown that patients with CTS have increased cross sectional area of the median nerve compared to controls
• However, there is no cut off point for diagnosis of CTS

MRI

• MRI can be used postoperatively to evaluate the quality of the release

Electrodiagnostic studies

• Nerve conduction studies measure conduction velocity of the median nerve in the carpal tunnel
• The role of electrodiagnostic testing is uncertain
• Electrodiagnostic testing is useful to
  • Confirm the diagnosis preoperatively, as a baseline for monitoring unexpected outcomes
  • Rule out other conditions such as radiculopathy, and for Workers Compensation cases
  • If repeat testing is necessary for a patient, be sure to send them to the same lab
• Mild CTS may not show any alterations in conduction
• Demyelination can occur with increased compression, resulting in conduction block or slowed conduction across the wrist
• EMG's may not normalize post op but they will improve
• In a 2002 systematic review of prospective studies
  • The sensitivity of nerve conduction studies for CTS ranged from 56 - 85%
  • The specificity ranged from 94 – 99%

Treatment

Non-operative

• Vitamin B6 does not significantly improve overall symptoms compared with placebo
• Wrist splint : Immobilise the wrist to avoid positions which increase carpal tunnel pressure
• NSAIDs
  • Relieve pain
  • Decrease inflammation
• Oral steroids
• Steroid injection
  • Injection of corticosteroids into the carpal tunnel to decrease inflammation
  • Have been shown to be better than placebo injections
  • A good response to an injection is prognositic of a better response to surgery compared to those who do not respond to the injection
  • May be used for therapeutic and prognostic reasons
  • Surgical decompression is recommended when injection no longer provides relief

Surgery

• Cut fascial covering of carpal tunnel to decrease pressure
• Options
  • Open carpal tunnel release (OTCR)
  • Endoscopic carpal tunnel release (ETCR)
    • No difference in outcomes at 1 year post op
    • Less postoperative pain
    • Shorter return to functional activities
    • The most significant, proven advantage of ECTR is faster mean return to work (18 days for ECTR vs. 38 days for OCTR)

Opponensplasty

• Patients with severe weakness and atrophy of the thenar muscles have a low likelihood of regaining their strength
• In these cases an opponensplasty may be indicated. Options include:
  • Camitz Procedure : transfer of palmaris longus tendon to the abductor pollicis brevis insertion site
  • Royle-Thompson Procedure
    • Transfer of ring FDS to thumb
    • Tendon is routed around ulnar border of the palmar fascia to act as a pulley
    • A slip of the superficialis is attached to the neck of the first metacarpal
    • Another slip is drawn over the MP joint and sutured into the hood mechanism of the proximal phalanx

Re-operation

• Reoperation for persistent CTS occurs in less than 5% of cases
• The most common reason for revision is technical error during primary release
  • Incomplete release of flexor retinaculum in 55%
  • Nerve adhesion in scar tissue in 32%
  • Nerve laceration in 6%
  • No known cause in 7%

Outcome

• Wrist splints
  • 80% patients report that a wrist splint alleviates symptoms within days
  • May minimize symptom severity and functional deficits for up to 3 months
• Oral steroids : May offer a benefit for up to 8 weeks
• Steroid injection
  • Improves symptoms in 75% of patients
  • May provide benefit for 2 weeks to 6 months
  • Long-term benefits have not been shown
• Surgery
  • Both OCTR and ECTR are safe and effective methods
  • Pain relief occurs within days
  • It takes several months for hand strength to return to preoperative levels
  • 70% of patients are either completely or partially satisfied with results
  • 79-90% patients report being free of nocturnal pain after surgery
  • 30% of patients over the age of 65 with chronic symptoms will not improve postoperatively

Complications

• Untreated, the syndrome can progress to
  • Permanent sensory loss
  • Paralysis of the thenar muscles
• Steroid injections
  • Infection
  • Rupture of tendons
  • Irritation of nerves
  • Possible systemic toxicity (hyperglycemia or hypertension)
• Surgery
  • General
    • Infection
    • Bleeding
    • Ligation of the median nerve
  • OTCR
    • Scar tenderness
    • Higher risk of bowstringing of flexor tendons, particularly when associated with a flexor tendon repair
  • ETCR
    • Visualization is not as good as with the open technique
    • The risk of major nerve or vessel injuries is not increased
    • There is higher risk of
      • Incomplete release
      • Revision surgery
      • Transient neuropraxia of the digital nerves

References