S138. Median nerve area and body mass index in carpal tunnel syndrome patients: A retrospective review of 1030 cases

Abstract

Obesity is a risk factor for carpal tunnel syndrome (CTS), but the association between median nerve cross-sectional area (CSA) and body mass index (BMI) is unclear. This is a retrospective review of patients presenting to the Duke Electromyography (EMG) Laboratory during 2013–2014 with a final diagnosis of CTS. US diagnosis of CTS was based upon median nerve cross-sectional area of >9 mm2 and/or wrist-to-forearm ratio of >1.4. EDx studies were the gold standard for diagnosis. The objective of this study is to determine if median nerve CSA is higher in overweight CTS patients. 1030 consecutive patients presenting to the Duke EMG Laboratory during 2013–2014 with a final electrodiagnostic (EDX) diagnosis of CTS were examined. Median nerve at the wrist (W-CSA), and forearm (F-CSA) were measured, and wrist-forearm ratio (WFR) calculated; patients were classified into BMI groups: I = underweight/normal, II = overweight, III = moderate obesity, IV = severe obesity, V = morbidly obesity. Statistical analysis was performed with ANCOVA test and Bonferroni correction using as covariates: age, gender, pregnancy and handedness. The mean age was 56 ± 14.0 (range from 20 to 90 years). 263 were men (36.8%) and 451 were women (63.2%, 10 women were pregnant). 521 patients were Caucasians, 162 Afro-Americans and 31 other ethnicities (Asians, Indians, Hispanic). 539 were right-handed, 174 left-handed and 1 was ambidextrous. We had 43 bifid median nerves, and 3 with persistent median artery. The mean body mass index (BMI) was 32.2 ± 8.0 (range from 15.5 to 112.1); patients were classified into BMI groups: Group I (underweight and normal weight) = 108; Group II (preobese) = 204; Group III (obese) = 182; Group IV (severely obese) = 102; Group V (morbidly obese) = 113. 5 patients were excluded because were outliers. There was a significant difference between BMI groups for W-CSA - right W-CSA mean 12.8 mm2 p = 0.000 and left W-CSA mean 11.7 mm2 p = 0.002, especially between: (1) underweight/normal and morbidly obese patients: right W-CSA mean 11.8 vs. 14.3 mm2 p = 0.001, left W-CSA mean 11.1 vs. 13.2 mm2 p = 0.004. (2) and between overweight and morbidly obese patients- right W-CSA mean 12.2 vs. 14.3 mm2 p = 0.000, left W-CSA mean 11.3 vs. 13.2 mm2 p = 0.001. There was no difference between BMI groups for forearm-CSA or the WFR. Higher BMI is associated with increased W-CSA in patients with CTS. In the current study, higher BMI is associated with increased W-CSA in patients with CTS.