Electrophysiologic Evaluation Of Autonomic Nerve Function In Patients With Type 2 Diabetes Mellitus

Objective To investigate the value of sympathetic skin response (SSR) and R-R interval variation test (RRIV) for diagnosing automatic dysfunction in patients with type 2 diabetes mellitus (T2DM) and to analyse the relationship between SSR values and diabetes duration, the blood glucose controlled.Methods SSR were carried out in 100 patients with T2DM and RRIV were carried out in 69 patients with T2DM, 30 healthy volunteers were served as controls. The Nicolet-Viking-Select system was used for SSR and RRIV detection. While SSR was performed, surface electrode was applied to stimulate median nerve at wrist, and SSR responses were recorded on the palm of both hands and the sole of both feet. The onset latency, N-wave latency, P-wave peak-to-peak amplitude and area of SSR were measured respectively. RRIV was tested with recordings made using two surface electrodes placed over the precordium. The values of RRIV at rest (R%) and during deep breathing (DB%) were calculated by the computer.Results 1) SSR was normally evoked in all the healthy controls both in the upper and lower limbs. The onset latency and N-wave latency of SSR prolonged significantly and peak-to-peak amplitude decreased and area reduced in the patient group as compared to the controls (P<0.05), While there was no significant difference in P-wave latency (P>0.05). 2) 72% patients with T2DM demonstrated abnormal SSR at least one limb. 88 upper limbs (88/200, 44.0%) and 112 lower limbs(112/200, 56.0%) had abnormal SSR, the abnormality rate was significantly higher in the upper limbs than that in lower ones (P<0.05). 3) The latencies of the onset and N-wave of SSR prolonged significantly in poorly glycemic controlled subgroup as compared to adequately glycemic controlled one, while there was no significant difference in the amplitude and area (P>0.05). 4) The SSR in latency, amplitude and area was of no significant difference in the subgroup with diabetes duration over 5 years as compared to the subgroup with diabetes duration below 5 years. 5) In 69 T2DM patients with combination test of SSR and RRIV, SSR showed abnormal in 44 cases (63.8%); and RRIV showed abnormal in 40 cases (57.9%); at least one of electrophysiological tests (SSR or / and RRIV) was abnormal in 55 cases (79.7%); in which the abnormality rate of combination tests of SSR and RRIV was higher than SSR and RRIV alone (P<0.05). 6)Thirty patients (43.5%) manifested at least one symptom or sign of autonomic dysfunction in 69 cases, in which the abnormality rate of electrophysiological tests was higher than the occurrence of clinical findings (79.7% vs 43.5%, P<0.05).Conclusion SSR is an objective electrophysiological method to assess the autonomic dysfunction related to T2DM. The abnormal SSR was significantly correlated to the blood glucose controlled, but not to diabetic duration. Combination tests of SSR and RRIV can reflect the sympathetic and parasympathetic function more comprehensively, and can increase the abnormality rate. Electrophysiological tests have higher sensitivity in evaluating the autonomic dysfunction than the clinical manifestation and may be a useful method for the early diagnosis of diabetic neuropathy.