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Diabetes Increases Median Nerve Cross-sectional Area But Not Disease Severity in Patients with Carpal Tunnel Syndrome
Colin H Beckwitt, MD, PhD1, William Schulz, BS2, John R Fowler, MD3, Jeffrey C Wera, MD1 and Karen Wasil, RN1, (1)University of Pittsburgh Medical Center, Pittsburgh, PA, (2)University of Pittsburgh, Pittsburgh, PA, (3)UPMC, Pittsburgh, PA

Introduction: Ultrasonography has recently emerged as a useful diagnostic modality for carpal tunnel syndrome (CTS). Diabetes mellitus is increasingly prevalent in the population and is a known risk factor for CTS. Given the increasing use of ultrasonography in the diagnosis of CTS, our goal was to evaluate the influence of diabetes on CTS severity as well as the cross-sectional area (CSA) of the median nerve in patients with CTS.
Materials & Methods: Patients with clinically diagnosed CTS were seen in the outpatient setting from October 2014-February 2021 and enrolled. The median nerve CSA was obtained along with patient reported severity measures: Boston Carpal Tunnel Syndrome Questionnaire (BCTSQ) and CTS-6. For patients with diabetes, additional parameters were collected including most recent A1c, insulin pharmacotherapy, or polypharmacy (>2 diabetes medications).
Results: 99 patients (122 nerves) without diabetes and 55 patients (82 nerves) with diabetes were recruited for the study. Patients in the diabetes group were more obese (Mean BMI 33.8 vs 29.9, p<0.01) and older (Mean age 61.9 vs 52.3, p<0.001). Overall, patients with diabetes had a significantly increased median nerve CSA (14.5 mm2) compared to patients without diabetes (12.8 mm2) (p=0.038). Obesity (BMI≥30) was associated with significantly higher median nerve CSA in all patients (p=0.041) but not in patients with diabetes (p=0.472). There was no significant difference in disease severity in patients with and without diabetes as reported by BCTSQ subscales FSS (p=0.171) or SSS (p=0.147) or CTS-6 score (p=0.787). In patients with diabetes, there was a significantly decreased median nerve CSA with A1c≥6.5 (p=0.008) and a trend to decreased CSA with polypharmacy (p=0.067). There was no influence of insulin therapy on median nerve CSA.
Conclusions: Diabetes is associated with higher median nerve CSA in patients with CTS of similar disease severity. The increased median nerve CSA in patients with diabetes may be reflective of diabetes-related microvascular changes. Obesity-related differences in median nerve CSA are not seen in patients with diabetes. Interestingly, the trend to decreased median nerve CSA in patients with suboptimal diabetic control (A1c≥6.5) may suggest eventual fibrotic changes to the median nerve. In summary, clinicians should be cautious with interpreting a larger median nerve CSA as more severe CTS in patients with diabetes.


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