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Ultrasound in diagnosis of carpal tunnel syndrome

OBJECTIVES: Carpal tunnel syndrome (CTS) is the most frequent entrapment neuropathy. While the diagnosis is based on clinical parameters, current gold standard for confirmation of CTS in most institutions are neurophysiological methods - electroneurography or electromyography. Recent studies show that some parameters of median nerve on ultrasound (US) can be used in diagnosis of CTS. Aim of this study was to evaluate suitability of US in confirmation of CTS, by comparing it with neurophysiological methods. METHODS: An ultrasound device Aloka Alpha10 with a high-frequency transducer of 13MHz and a custom preset was used for imaging. Different parameters of the median nerve (MN) were measured using built-in functions. Cross-sectional area (CSA) of MN was assessed at the inlet and in the middle of the carpal tunnel and flattening ratio was calculated. Patient group consisted of 20 consecutive patients, with bilateral or unilateral CTS symptoms, which were subjected to neurophysiological testing prior to ultrasound examination. Control group had 25 asymptomatic patients and did not undergo examination in an elecrophysiological lab. RESULTS: Bilateral symptoms of CTS were present in 75% of patients. Compared to control group, patients with CTS had higher average CSA (9.7 vs. 13.9 mm2, respectively). By using current standard cut-off value for diagnosing CTS of 10mm2 , sensitivity of 91, 2% and specificity of 86, 1% was established. EMNG correctly detected 92.8% of symptomatic CTS with specificity of 86, 7%. Correlation between semiquantitative values of symptoms and EMG findings was 0.39. CONCLUSION: Our findings show comparable sensitivity and specificity of US and EMNG in detection of CTS, using CSA at carpal tunnel inlet as key parameter. By not causing any discomfort in patients, and with an advantage of offering data on possible visible etiology of neuropathy inside carpal tunnel, ultrasound could prove to be a convenient method in diagnostic work-up of this condition.

CTS; carpal tunnel syndrome; ultrasound; sonography; median nerve; peripheral nerve; diagnosis

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