Ultrasound Assessment of Carpal Tunnel Syndrome in Comparison with Nerve Conduction Study: A Case-control Study

Abstract

Introduction: Carpal Tunnel Syndrome (CTS) is the entrapment neuropathy which is diagnosed based on the clinical history, examinations and the electrophysiological findings. The Cross- sectional Area (CSA) measurement of the median nerve has emerged as an alternative to Nerve Conduction Studies (NCS) for diagnosis of CTS. This study was done to correlate NCS and Ultrasonography (USG) in clinically diagnosed CTS patients. Aim: To evaluate the diagnostic value of Cross-sectional Area (CSA) of median nerve at carpal tunnel inlet in patients with clinically and NCS confirmed Carpal Tunnel Syndrome (CTS) and to assess severity of the syndrome by NCS and its correlation with USG results. Materials and Methods: This was a hospital based, case-control study done on a total of 109 patients of CTS and analysed during the period from June 2017 to June 2019. Total 203 hands of the patients with abnormal NCS formed case group while 101 hands from healthy volunteers constituted the control group. All the patients underwent neurological evaluation by Boston Carpal Tunnel Questionnaire (BCTQ) and were divided into mild, moderate and severe according to the score. An electromyography machine was used to perform electrophysiological studies of both the limbs in all subjects. CTS was diagnosed electro-diagnostically based on the American Association of Neuromuscular and Electrodiagnostic Medicine (AANEM) guidelines and were classified as mild (Grades 1 and 2), moderate (Grades 3 and 4), and severe (Grades 5 and 6) grades using Bland’s electrophysiological grading scale. USG was performed for all the subjects and all the data of various investigations was analysed using Statistical Package for Social Sciences (SPSS) version 22.0 software. Chi-square test and Mann Whitney U-test were used as test of significance for qualitative data. Results: The mean age of subjects was 44.38±9.561 years. Strongly significant association was observed in BCTQ symptom, functional and total scores with NCS severity grading (p-value <0.001). Moderately significant association was found between BCTQ symptom and total scores with USG severity grading (p-value<0.02). Tunnel grade and NCS grade were found significantly correlated (p-value <0.001). The mean CSA cut-off value of 8.5 mm² at the inlet of carpal tunnel had a good sensitivity 86.21%, specificity 83.17%, Positive Predictive Value (PPV) 91.1% and Negative Predictive Value (NPV) 75%. Conclusion: The diagnostic accuracy of USG assessment and NCS was found to be correlated comparably and complement each other in all grades of CTS. USG, can be considered a preferable screening tool by the patients of CTS due to its painless nature and easy accessibility. It requires minimal time and many a times detects those structural abnormalities which have great therapeutic implications. In mild CTS cases, USG should always be combined with NCS for proper diagnosis as USG might give negative result.