In carpal tunnel syndrome, the median nerve is compressed in the carpal tunnel of the wrist.
Description
• Compression neuropathy of median nerve in the wrist, resulting in pain and/or paresthesias in thumb, forefinger, and middle finger of somewhat variable distribution
ICD-9 code
• 354.0 carpal tunnel syndrome
Incidence/prevalence
• >41% of all repetitive motion disorders in United States
• Symptoms of pain, numbness, or tingling in the hands are common in the general population (14.4% prevalence), but only 20%-50% of symptomatic patients found to have carpal tunnel syndrome (CTS)
• 11% women and 3.5% men expected to develop CTS by age 70 years
Causes
• Most common cause is repetitive motion; not clearly due to inflammation
• Swelling in carpal tunnel may also be due to
— Anatomic aberrations
— Infectious causes
— Inflammatory conditions
— Metabolic conditions
— Increased fluid volume in canal
• Patterns of use that may increase risk
— Repetitive flexion/extension, e.g., cashier, letter sorter
— Weight bearing on extended wrist, e.g., jackhammer operator
— Vibration, e.g., assembly worker
— Cold temperatures, e.g., food processing
• Keyboard and computer use does not appear to be a risk factor.
Patient history
• Awakening at night with numb hands
• Paresthesias and numbness in first three digits, often with aching in median-nerve distribution
• Pain may become diffuse and can radiate up arm.
• Symptoms worse with repetitive use and fixed position, e.g., driving, sleeping
• Sometimes weakness in intrinsic hand muscles (innervated by median nerve muscles)
• Ask “What do you do when this pain occurs?” (flick sign positive if patient flicks wrist and hand)
Physical exam
• May find decreased sensation in median-nerve distribution (from thumb through middle of fourth finger)
• Look for muscle atrophy: flattening of thenar eminence (muscle bulk at base of thumb) may occur with prolonged CTS)
• Check for objective weakness: Have patient abduct thumb against resistance
• Findings that predict CTS on electrodiagnostic testing
— Classic or probable distribution of hand involvement (symptoms affecting first three digits)
— Hypalgesia
— Weak thumb abduction
• Phalen and Tinel signs are neither sensitive nor specific for CTS.
• Maneuvers to reproduce or intensify symptoms in conditions that may be misdiagnosed as CTS
— Forced full flexion of neck
— Turn head toward involved side (Spurling maneuver)
— Thoracic outlet maneuvers