Carpal Tunnel Syndrome

Carpal tunnel syndrome (CTS) is a complex of signs and symptoms caused by compression of the median nerve as it crosses the carpal tunnel. Presentation is with pain and paresthesia of the dermatomal target tissues innervated by the median nerve as well as weakness and atrophy of the nerve’s myotomal targets. Risk factors that cause a predisposition to CTS include obesity, female sex, pregnancy, diabetes, inflammatory conditions, genetic predisposition, and occupational factors. A clinical diagnosis may be made on the basis of history and physical examination and confirmed with electrodiagnostic testing. Conservative management includes splinting and physical therapy; more severe cases may require surgical correction.

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Overview

Anatomy

  • The median nerve emerges from the brachial plexus with contributions from the C6, C7, C8, and T1 nerve roots.
  • Roots C6 and C7 supply the median sensory fibers, which in turn give sensation to the thenar eminence and the 1st 3½ digits of the hand.
  • Roots C8 and T1 supply the motor fibers to the forearm and hand musculature innervated by the median nerve.
  • As the median nerve passes through the antecubital fossa, it lies medial to the brachial artery deep within the forearm. 
  • In the upper portion of the forearm, the median nerve innervates:
    • Pronator teres
    • Flexor carpi radialis
    • Palmaris longus
    • Flexor digitorum superficialis
  • The median nerve then gives off a peripheral branch, forming the anterior interosseous nerve.
  • The anterior interosseous nerve innervates:
    • Pronator quadratus (proximal to the wrist)
    • Flexor pollicis longus 
    • Flexor digitorum profundus I and II muscles
  • The median nerve proper runs parallel to the anterior interosseous nerve in the forearm.
  • Proximal to the wrist, the cutaneous sensory branch of the median nerve branches off to provide sensation to the lateral half of the palm.
  • Because the palmar branch of the median nerve passes over, and not through, the carpal tunnel, sensory changes over the thenar eminence are not typically observed with carpal tunnel syndrome (CTS).
  • The carpal tunnel is formed by the transverse carpal ligament (flexor retinaculum) superiorly and the carpal bones inferiorly.
  • The median nerve proper and the 9 flexor tendons of the forearm musculature pass through the tunnel.
  • Upon exiting the carpal tunnel, the median nerve provides sensory and motor innervation to the hand.
  • The hand muscles innervated by the median nerve:
    • Abductor pollicis brevis
    • Flexor pollicis brevis (superficial head)
    • Opponens pollicis
    • 1st and 2nd lumbricals

Mnemonic:

Median-innervated hand muscles (Meat-LOAF):

  • Meat: median nerve
  • L: 1st and 2nd lumbricals
  • O: opponens pollicis
  • A: abductor pollicis brevis
  • F: flexor pollicis brevis
Structure and contents of the carpal tunnel

Structure and contents of the carpal tunnel

Image by Lecturio.

Epidemiology

  • Common disorder among adults
  • Prevalence in general population: 1%–5%.
  • Female > male by 3:1
  • Prevalence highest in obese women
  • Prevalence lowest in thin and average-sized men

Etiology (risk factors)

  • Obesity
  • Female sex
  • Pregnancy
  • Diabetes
  • Rheumatoid arthritis
  • Osteoarthritis of the hand
  • Hypothyroidism
  • Connective tissue disorders
  • Preexisting median mononeuropathy
  • Genetic predisposition
  • Aromatase inhibitor use
  • Workplace factors:
    • Repetitive hand and wrist use
    • Forceful hand and wrist use
    • Work with vibrating tools
    • Sustained wrist or palm pressure
    • Prolonged wrist extension and flexion
    • Use of hands in cold temperatures
  • Trauma

Pathophysiology

The pathophysiology of narrowing of the carpal tunnel and median nerve dysfunction are multifactorial.

  • Narrowing of the carpal tunnel:
    • Congenitally small anatomic space 
    • Mass lesions encroaching on anatomic space: 
      • Cysts
      • Neoplasms
      • Persistent median artery 
    • Edema or inflammation from systemic diseases:
      • Diabetes
      • Osteoarthritis
      • Rheumatoid arthritis
    • Inflammation/thickening of the flexor tendons passing through the carpal tunnel alongside the median nerve
    • Noninflammatory fibrosis affecting the subsynovial connective tissue surrounding the flexor tendons
  • Mechanical compression of the median nerve:
    • Increased pressure in the carpal tunnel may cause:
      • Direct nerve injury
      • Impaired axonal transport
      • Compression of vessels in the perineurium → median nerve ischemia
    • Upper-extremity postural abnormalities
  • Median nerve develops an “hourglass” deformity within the carpal tunnel due to:
    • Edema and thickening of vessel walls within the endoneurium and perineurium
    • Noninflammatory synovial fibrosis and vascular proliferation
    • Fibrosis
    • Myelin thinning
    • Nerve-fiber degeneration and regeneration
  • Vascular proliferation and fibrosis are associated with increased prostaglandin E2 and vascular endothelial growth factor expression.

Clinical Presentation

  • Common symptoms:
    • Pain/discomfort in the hand, wrist, and forearm
    • Paresthesia in the median-nerve distribution of the affected hand(s) (e.g., heaviness, tingling, pins-and-needles sensation)
    • Subjective weakness or clumsiness of the hand
    • Occurrence of any of these symptoms in the median distribution
  • Common signs:
    • Sensory deficit in the median-nerve distribution of the affected hand(s)
    • Objective weakness or clumsiness of the hand
    • Thenar muscle atrophy
  • Provocative factors:
    • Sleep:
      • Wrist-flexion posturing
      • Relative immobility/flat positioning (i.e., decreased perfusion)
    • Sustained hand or arm positions
    • Repetitive actions of the hand or wrist
  • Alleviating factors:
    • Changes in hand/wrist posture (wrist extension)
    • Shaking the hand (i.e., improved perfusion)

Diagnosis

Carpal tunnel syndrome is a clinical diagnosis. A combination of clinical findings with confirmatory electrodiagnostic testing is more accurate for diagnosis.

Examination

  • Objective sensory and motor deficits may be present (absence does not rule out a diagnosis).
  • Sensory deficits occur late in the course of CTS:
    • Affect the median innervated fingers
    • Spare the thenar eminence
  • Objective weakness occurs in advanced CTS:
    • Limited to thenar eminence muscles
    • Causes weakness of thumb abduction and thumb opposition
  • Atrophy of the thenar eminence may be present.

Provocative maneuvers

  • Phalen maneuver: 
    • Dorsal aspect of hands pressed together with the wrists in full flexion and the elbows in 0–30 degrees of flexion 
    • A positive sign is defined as pain and/or paresthesia in median innervated fingers with 1 minute of wrist flexion.
  • Tinel test:
    • Firm percussion over the course of the median nerve proximal to or on top of the carpal tunnel
    • A positive test is defined as pain and/or paresthesia in median innervated fingers on percussion over the median nerve.
  • Manual carpal compression:
    • Applying pressure over the transverse carpal ligament
    • Deemed positive if pain and/or paresthesia noted in median innervated fingers within 30 seconds of compression
  • Hand elevation test:
    • Raising hands above the head for 1 minute
    • Deemed positive if pain and/or paresthesia noted in median innervated fingers within 30 seconds of elevation
Tests for carpal tunnel syndrome

Provocative maneuvers for clinical evaluation of carpal tunnel syndrome

Image by Lecturio.

Electrodiagnostic testing

  • Nerve conduction velocity:
    • Involves measurement of conduction velocity across the carpal tunnel and determination of the amplitude of sensory and motor responses.
    • Nerve compression causes damage to the myelin sheath manifesting as delayed distal latencies and slowed conduction velocities.
    • Sustained or severe compression leads to axonal loss resulting in the reduction of median-nerve action potential amplitude.
    • Gold standard for diagnosis; highly sensitive and specific
  • Electromyography:
    • Useful to exclude other conditions
    • Useful to assess the severity of CTS if surgical decompression is being considered

Imaging

Imaging is useful if structural abnormality is suspected.

  • Neuromuscular ultrasound shows a significant increase in cross-sectional area of the median nerve.
  • MRI is reserved for unusual cases to rule out mass lesions.

Grading/staging

Clinical grading of CTS severity:

  • Mild: 
    • Numbness, tingling, or discomfort in the median-nerve distribution 
    • No sensory loss or weakness
    • No sleep disruption
    • No difficulty with hand function
    • No interference with activities of daily living
  • Moderate:
    • Sensory loss with median distribution
    • Nocturnal symptoms occasionally disrupt sleep.
    • Symptoms may interfere slightly with hand function.
    • No interference with activities of daily living
  • Severe:
    • Weakness in the median distribution
    • Nocturnal symptoms routinely disrupt sleep.
    • Symptoms are disabling and prevent carrying out ≥ 1 activities of daily living.

Electrodiagnostic grading of CTS severity:

  • Mild:
    • Prolonged sensory latencies with normal motor studies
    • No evidence of axonal loss
  • Moderate:
    • Abnormal median sensory latencies
    • Relative or absolute prolongation of median motor distal latency
    • No evidence of axonal loss
  • Severe: evidence of axonal loss

Management

Management is based on the acuity and severity of clinical symptoms and the degree of neurogenic injury as assessed by electrodiagnostic studies. 

Nonsurgical treatment options

For individuals with mild to moderate CTS, the rate of successful outcomes is 20%–93%. Options include:

  • Wrist splinting
  • Glucocorticoid injection
  • Oral glucocorticoids
  • Perineural dextrose injection
  • Yoga
  • Carpal bone mobilization (physical therapy or manipulative therapy)
  • Therapeutic ultrasound therapy

Surgical decompression

  • Indications include:
    • Mild CTS unresponsive to conservative measures
    • Moderate to severe CTS associated with axonal loss or denervation
  • Open carpal tunnel release technique
  • Endoscopic carpal tunnel release technique
  • Ultrasound-guided minimally invasive carpal tunnel release technique

Prognosis

  • Symptoms in untreated individuals with minimal or mild compression tend to worsen over 10–15 months.
  • Factors that predict progression:
    •  Positive Phalen test
    • Bilateral disease
  • Treatment with splinting or surgical decompression may lead to complete or marked improvement at 1 year in 70%–90% of individuals.

Differential Diagnosis

  • Cervical radiculopathy: C6 or C7 nerve-root involvement may present with arm pain and paresthesia similar to that of CTS. Typically, there is also the presence of neck pain exacerbated with neck movement; radiation of pain from the neck to the shoulder and arm; reduced reflexes; weakness of proximal arm muscles involving elbow flexion, extension, and arm pronation; and sensory loss in the palm or forearm outside the region of sensory abnormalities caused by CTS. 
  • Brachial plexopathy: manifests with predominant involvement of an individual nerve of the brachial plexus, such as the axillary, long thoracic, anterior interosseous, radial, median, or musculocutaneous nerve. However, examination findings in brachial plexopathy reveal weakness, sensory loss, or diminished reflexes outside the distribution of the median nerve and usually involve fibers from > 1 spinal nerve root.
  • Median neuropathy: occurs in the proximal forearm where the nerve passes through the pronator teres muscle. The clinical presentation of median neuropathy may include forearm pain and sensory loss involving the entire lateral palm. Clinical findings include sensory loss over the thenar eminence (which is spared in CTS) and weakness of thumb flexion, wrist flexion, and arm pronation (which are median innervated muscles proximal to the carpal tunnel). Electromyography or nerve conduction studies are required to localize the exact site of compression.
  • Motor neuron disease (e.g., amyotrophic lateral sclerosis [ALS]): presents with asymmetric hand involvement that predominantly involves the thenar hand intrinsic muscles. The absence of sensory symptoms argues against CTS. The disease ALS never presents with the weakness of a single muscle.

References

  1. Kothari MJ. (2020). Carpal tunnel syndrome: etiology and epidemiology. Retrieved August 17, 2021, from https://www.uptodate.com/contents/carpal-tunnel-syndrome-etiology-and-epidemiology
  2. Kothari MJ. (2021). Carpal tunnel syndrome: Clinical manifestations and diagnosis. In Shefner J.M. et al. (Ed.), UpToDate. Retrieved August 18, 2021, from https://www.uptodate.com/contents/carpal-tunnel-syndrome-clinical-manifestations-and-diagnosis
  3. Kothari MJ. (2020). Carpal tunnel syndrome: Treatment and prognosis. Retrieved August 18, 2021, from https://www.uptodate.com/contents/carpal-tunnel-syndrome-treatment-and-prognosis
  4. Hunter AA, et al. (2021). Surgery for carpal tunnel syndrome. Retrieved August 18, 2021, from https://www.uptodate.com/contents/surgery-for-carpal-tunnel-syndrome
  5. Steinberg D. (2020). Carpal tunnel syndrome. MSD Manual Professional Version. Retrieved August 18, 2021, from https://www.msdmanuals.com/professional/musculoskeletal-and-connective-tissue-disorders/hand-disorders/carpal-tunnel-syndrome
  6. Ashworth NL. (2020). Carpal tunnel syndrome. Retrieved August 18, 2021, from https://emedicine.medscape.com/article/327330

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