How is carpal tunnel syndrome (CTS) diagnosed?

Diagnosis of Carpal Tunnel Syndrome

Carpal tunnel syndrome is diagnosed primarily through clinical evaluation combined with electrophysiologic studies, with imaging reserved only for selected circumstances when the diagnosis remains unclear. 1, 2

Primary Diagnostic Approach

Clinical Evaluation

The diagnosis begins with identifying characteristic symptoms and physical examination findings:

• Classic symptoms include pain, numbness, and tingling in the median nerve distribution (palmar aspect of thumb, index and middle fingers, and radial half of ring finger) 3
• Night pain is highly sensitive (96% sensitivity) and should be specifically queried 4
• The flick sign (patient shakes hand to relieve symptoms) is a characteristic clinical finding 3

Physical Examination Tests

When performing the physical exam, prioritize these validated maneuvers:

• Durkan's compression test has the highest sensitivity (89%) among physical tests—apply direct pressure over the carpal tunnel for up to 30 seconds 4
• Phalen's maneuver (wrist flexion test) has high overall accuracy and should be performed for 5 minutes 4, 5
• Tinel's sign (nerve percussion test) is more specific (71%) for moderate to severe CTS with axonal damage, though less sensitive 4, 5

Hand Diagram Assessment

• Self-administered hand diagrams showing symptom distribution have both good sensitivity (76%) and specificity (76%) 4
• This structured approach helps document the pattern of sensory symptoms objectively 5

Confirmatory Testing

Electrophysiologic Studies

Electrodiagnostic testing is the gold standard confirmatory test and should be obtained in the following situations:

• When clinical presentation is atypical and diagnosis is uncertain 3
• Before surgical decompression to determine severity and surgical prognosis 3
• To rule out alternative diagnoses that overlap with CTS presentation 5

Sensory and motor nerve conduction studies comparing the median nerve segment across the wrist to another nerve segment are the most sensitive and accurate neurophysiologic techniques 6

Imaging Studies

Ultrasound is the preferred first-line imaging modality when imaging is needed because it is more cost-effective and widely available 7:

• Median nerve cross-sectional area ≥10 mm² at the carpal tunnel inlet is the primary diagnostic criterion 7
• Ultrasound demonstrates high sensitivity and specificity compared to clinical assessment and electrophysiologic studies 2, 7
• Can identify anatomic variants (bifid median nerve, persistent median artery) and space-occupying lesions that may cause symptoms 7
• Can detect associated tendon pathology such as tenosynovitis 7

MRI without contrast may be appropriate in selected circumstances but is typically not indicated for routine CTS diagnosis 1, 2, 7:

• Can show median nerve enlargement and flattening, flexor retinaculum bowing, and space-occupying lesions 7
• Generally reserved for cases where ultrasound is inconclusive or unavailable 7

CT, CT arthrography, bone scan, and x-ray arthrography are not routinely used to diagnose carpal tunnel syndrome 1, 2

Diagnostic Algorithm for Maximum Accuracy

If a patient has all four of the following, the probability of correctly diagnosing CTS is 86%: 4

• Abnormal hand diagram showing median nerve distribution
• Abnormal Semmes-Weinstein monofilament sensibility testing in wrist-neutral position
• Positive Durkan's compression test
• Night pain

If all four conditions are normal, the probability of CTS is less than 1% 4

Laboratory Testing Considerations

• Routine laboratory testing is NOT recommended for patients with typical carpal tunnel syndrome, as it generates more false positives than true positives 2
• Consider targeted testing (HbA1c, TSH, vitamin B12) only when there are signs suggesting underlying systemic disease or reversible causes of neuropathy 2
• Bilateral CTS without obvious cause (no rheumatoid arthritis or trauma) may warrant evaluation for systemic conditions including cardiac amyloidosis 7

Common Pitfalls to Avoid

• Do not rely on electrodiagnostic testing alone—the combination of clinical tests (hand diagram, sensibility testing, Durkan's test, and night pain) provides equivalent diagnostic power without adding electrodiagnostic studies 4
• Avoid ordering MRI routinely—it is not indicated for typical CTS and should be reserved for unclear cases 1, 7
• Do not use ineffective tests—vibrometry, current perception testing, and two-point discrimination have considerable subjective components and are not as sensitive as traditional nerve conduction studies 6
• Remember that other conditions can mimic CTS—cervical radiculopathy, polyneuropathy, and thoracic outlet syndrome require vigorous differential diagnosis 8