Background Carpal Tunnel Syndrome (CTS) is a neural affection that in diabetic patients can be associated with polyneuropathy (DP). In rheumatologists’s practice, ultrasonography represents a useful tool in the study of median nerve entrapment pathology since increased median nerve Cross-section area (CSA) at the carpal tunnel is considered both sensitive and specific in diagnosis of CTS(1,2). However, previous studies on diabetics showed a diffuse increase of peripheral nerve CSA in patients with DP (3), making standard reference values for general population not applicable in these patients.
Objectives The aim of this study was to assess median nerve CSA cut-off values for the diagnosis of CTS in a population of diabetic patients, with or without polyneuropathy.
Methods We enrolled all consecutive diabetic patients, regardless the presence of CTS or DP symptoms but without other risk factors for neuropathy, who reached the Diabetology Clinic of this hospital in November 2012 for routine controls. Patients underwent median nerve conduction study (EMG) of the symptomatic hand or the dominant one-if asymptomatic for CTS. For the diagnosis of DP were also assessed tibial, peroneal and sural nerve. CSA measurement of the median nerve was performed at the tunnel inlet. ROC curves were employed to determine the optimal cut-off values for ultrasonographic CSA in all patients and in subgroups with or without DP. EMG was considered the gold standard for diagnosis of CTS.
Results 39 patients (20 female), mean age 64yo (range 27-83yo, SD 12,47), were enrolled. Mean duration of disease was 18,6 y (range 1-64y, SD 13,39). Mean values of median CSA in the cohort and in patients with and without DP were respectively 11,23 mm2 (SD 2,6), 12,4 mm2 (SD 2,7) and 10,5mm2 (SD 2,26). ROC analysis showed the following CSAs as the best values for sensitivity and specificity: total cohort 11,5 mm2 (61,5% sensitivity and a 85% specificity - AUC 0,796), patients with DP 12mm2 (sensitivity 69% with a 100% specificity, AUC 0,846), 10,5mm2 in patients without DP (sensitivity 61%, specificity 64%, AUC 0,734). The standard cut-off value for the general population of 10,5mm2 yielded in our patients the following results: total cohort 65% and 62%, diabetes with DP 60% and 50% and diabetes without DP 61% and 64% of sensitivity and specificity respectively.
Conclusions In patients with diabetes and DP US CSA cut-off values for diagnosis of CTS should be raised to obtain a better sensitivity and specificity while for patients with diabetes but without DP the same cut-off values of the general population can be used. For patients with diabetes but uncertain about the presence of DP, the optimal cut-off is 11,5mm2.
Wong SM et al, Discriminatory sonographic criteria for the diagnosis of carpal tunnel syndrome. Arthritis Rheum 2002 46(7): 1914–1921
Mondelli M, Filippou G. Diagnostic utility of ultrasonography versus nerve conduction studies in mild carpal tunnel syndrome. Arthritis Rheum 2008 59: 357-366
Watanabe T, Ito H, Sekine A et al, Sonographic evaluation of the peripheral nerve in diabetic patients. J Ultraound Med 2010; 29:697- 708
Disclosure of Interest None Declared