Autonomic and somatic peripheral nerve function and the correlation with neuropathic pain in diabetic patients

Pupillary and cardiovascular autonomic functions were examined in 25 diabetic patients with and 25 diabetic patients without painful neuropathy. There were no significant differences between the groups with regard to age, duration of diabetes or glycaemic control. Vibratory perception, reflecting peripheral large fibre function, was more severely disturbed in the symptomatic group (P = 0.003). Thermal discrimination thresholds (TDTs), reflecting somatic small fibre function, were abnormal in all symptomatic patients and the difference between patients with and without symptoms was more pronounced (P less than 0.0001), than for large fibre function. The latency of the constriction reaction of the pupil (parasympathetic function) was prolonged in 17 symptomatic patients and in 6 patients without pain; it proved to be significantly more prolonged in the group with painful neuropathy (P = 0.001). Cardiovascular autonomic neuropathy was present in 29 patients, especially in patients with painful neuropathy (22 in the group with painful neuropathy, 7 in the group without pain). There was a significant correlation between results of TDT and respectively pupillary and cardiovascular autonomic function tests (kappa coeëfficient: 0.63 and 0.56, respectively, P less than 0.0001). We conclude that autonomic dysfunction is often present in patients with painful neuropathy. However, thermal sensory dysfunction is better correlated with the presence of symptoms than cardiovascular and pupillary autonomic dysfunction.