Large and small nerve fiber function in painful diabetic neuropathy.

Vibratory perception thresholds (VPTs) and thermal discrimination thresholds (TDTs), reflecting large nerve fiber function and small nerve fiber function, respectively, were determined in 20 diabetics with painful sensory polyneuropathy and in 20 diabetics without neuropathic symptoms. VPTs were elevated in 27 patients and proved to be significantly higher in the group with painful neuropathy (p less than 0.01). Yet in three symptomatic patients, VPTs were normal. TDTs were abnormal in 35 cases and the difference between patients with and patients without symptoms was more pronounced (p less than 0.001). All patients with painful neuropathy had elevated TDTs. These findings confirm the relationship between pain in diabetic neuropathy and the affection of small fiber function. When monitoring of peripheral nerve function in patients with painful diabetic neuropathy is required, quantitation of thermal cutaneous sensation provides useful information on the function of small nerve fibers.