Effects of current perception threshold in evaluating the peripheral nerves in diabetic patients

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Objective To evaluate the impairment of large and small fibers of peripheral nerves in patients with diabetes mellitus according to the current perception threshold (CPT) comparing with nerve conduction studies (NCS) and sympathetic skin response (SSR). Methods Fourty-nine diabetic patients were enrolled from August to December 2014 in Tianjin Third Central Hospital. The CPT was examined by the Neurometer® CPT/C in diabetic patients and 23 healthy subjects. Electrical stimulations of 2 000, 250 and 5 Hz were delivered respectively to the first toe distal section, the bottom of the knee-patella middle line and the index finger distal section. NCS and SSR were performed in diabetic patients. The patients were divided into normal NCS (NCSN) group and abnormal NCS (NCSA) group according to the results of the nerve conduction. According to the results of SSR, the patients were divided into normal SSR (SSRN) group and abnormal SSR (SSRA) group. Results In three testing areas, the CPT in NCSN group had no significant difference compared with control group, which was tested by different frequency; NCSA group had increased CPT (393.5±68.4, 213.1±39.7, 172.5±52.8, 221.6±48.0, 91.7±33.1, 76.2±27.8, 274.0±48.4, 120.1±26.6, 75.3±21.9)compared with control group(278.1±53.6, 128.9±46.7, 78.7±28.7, 149.3±54.6, 52.3±23.2, 41.9±18.7, 214.2±46.0, 96.0±29.3, 48.6±17.0; F=36.277, 40.827, 50.301, 10.240, 12.837, 13.832, 11.749, 5.559, 17.412, all P<0.01). At the first toe section, CPT decreased in SSRN group (91.0±29.0, 55.2±21.3) compared with control group (128.9±46.7, 78.7±28.7; F=23.071, 22.646, both P<0.05), which was tested by the currents of 250 Hz and 5 Hz frequency. In three testing areas, the SSRA group had increased CPT compared with control group, which was tested by different frequency. Conclusion Hyperesthesia as an early manifestation of small fiber damage can be detected by CPT in diabetic patients; CPT has no advantage in the evaluation of large fiber damage. Key words: Diabetic peripheral neuropathy; Current perception threshold; Nerve conduction; Sympathetic skin response