What are the appropriate tests and steps to evaluate suspected carpal tunnel syndrome?

Carpal Tunnel Syndrome Testing

Diagnose carpal tunnel syndrome primarily through clinical evaluation combined with electrodiagnostic studies, reserving imaging only for atypical presentations where the diagnosis remains unclear. 1

Clinical Evaluation

Key Symptoms to Elicit

• Pain and paresthesias in the median nerve distribution: thumb, index finger, middle finger, and radial half of the ring finger 2, 3
• Nocturnal symptoms: patients typically awaken at night with pain and abnormal sensations, relieved by shaking the hand 4, 5
• Radiation patterns: pain frequently radiates proximally into the forearm and occasionally to the shoulder 4

Physical Examination Maneuvers

• Flick sign: patient shakes hand to relieve symptoms 2
• Phalen maneuver: wrist flexion test (though diagnostic value is limited) 4, 2
• Tinel test: percussion over median nerve at wrist (though diagnostic value is limited) 4
• Median nerve compression test: direct pressure over carpal tunnel 2

Important caveat: No single physical examination test is diagnostic on its own; the combination of clinical findings establishes the diagnosis. 4, 5

Electrodiagnostic Testing

When to Order

Obtain electrodiagnostic studies when clinical examination is positive AND surgical management is being considered, as these tests determine severity and surgical prognosis. 6

Standard Testing Protocol

• Routine median nerve conduction studies: prolonged terminal latency of motor or sensory nerve found in most CTS cases 4
• Sensory nerve conduction: most sensitive early indicator 4
• Motor nerve conduction: may show prolonged distal latency 4

Advanced Testing for Equivocal Cases

When routine studies are inconclusive, use more sensitive methods: 4

• Segmental sensory conduction study across the carpal tunnel with median stimulation at midpalm
• Comparison of median and ulnar sensory nerve latencies at ring finger
• Comparison of median and radial sensory nerve latencies at thumb
• Difference between median motor latency to second lumbrical and ulnar motor latency to interossei muscles

Electrodiagnostic testing is the gold standard objective measure of median nerve dysfunction, but cannot make the diagnosis without appropriate clinical symptoms. 5, 7

Imaging Studies

When Imaging Is Appropriate

Reserve imaging for selected atypical cases where clinical and electrodiagnostic findings are unclear or when anatomic variants are suspected. 1, 6

Ultrasound (First-Line Imaging)

Ultrasound is the preferred imaging modality when imaging is needed due to cost-effectiveness and availability. 1

Primary diagnostic criterion: median nerve cross-sectional area ≥10 mm² at the carpal tunnel inlet 1

Additional ultrasound findings: 1

• Enlargement and flattening of the median nerve
• Bowing of the flexor retinaculum
• Space-occupying lesions (ganglion cysts, tumors)
• Anatomic variants (bifid median nerve, persistent median artery)
• Tendon pathology (tenosynovitis)

Scanning technique: 1

• Patient sitting with hand resting on thigh or examination table
• Volar transverse scan at carpal tunnel
• Volar longitudinal scan
• High-frequency transducers (≥10 MHz)
• Dynamic examination with active finger flexion/extension

MRI

MRI can detect CTS with high accuracy but is typically not indicated for routine evaluation. 1 Consider MRI only when ultrasound is inconclusive or detailed soft-tissue characterization is required. 1

Imaging NOT Recommended

Do not order these studies for routine CTS evaluation: 1

• CT (with or without contrast)
• CT arthrography
• Bone scintigraphy
• X-ray arthrography
• Plain radiographs (unless bony abnormality or arthritis suspected)

Laboratory Testing

When to Consider Labs

Avoid routine laboratory testing in typical CTS presentations, as it generates more false positives than true positives. 6

Consider targeted testing only when atypical features suggest systemic disease: 6

• HbA1c (diabetes screening)
• TSH (thyroid dysfunction)
• Vitamin B12, B6, folate levels
• Serum protein electrophoresis with immunofixation (amyloidosis, especially if bilateral CTS without trauma or rheumatoid arthritis) 1

Critical Pitfalls to Avoid

• Do not rely on physical examination tests alone: Tinel and Phalen tests have limited diagnostic value and must be combined with clinical history and electrodiagnostic studies 4, 5
• Do not proceed with imaging in typical cases: routine imaging is not indicated when clinical presentation and electrodiagnostic studies are consistent with CTS 1
• Do not skip electrodiagnostic testing before surgery: these studies are essential for determining severity and surgical prognosis 6, 2
• Do not diagnose CTS based solely on electrodiagnostic findings: history must include CTS symptom criteria and exclude other causes 7