Differences in Peripheral and Autonomic Nerve Function Measurements in Painful and Painless Neuropathy: A clinical study

OBJECTIVE: To examine the differences in peripheral and autonomic nerve function measurements between diabetic patients without neuropathy (group 1, n = 38, mean age 50.9, range 29-71 years), with painless neuropathy (group 2, n = 32, mean age 49.2, range 30-71 years), and with painful neuropathy (group 3, n = 52, mean age 51.5, range 28-73 years). RESEARCH DESIGN AND METHODS: The evaluation of neuropathy was based on clinical symptoms, signs, and quantitative sensory testing, including current perception threshold (CPT) with a neurometer and electrophysiology. RESULTS: The Neuropathy Symptom Score and the Neuropathy Disability Score were higher in patients with painful neuropathy compared with patients with painless neuropathy (6.8 +/- 2.7 vs. 0.5 +/- 0.8 [mean +/- SD], P < 0.0001, and 12.5 +/- 6.2 vs. 8.6 +/- 6.8, P < 0.01, respectively). In contrast, no differences were found in the quantitative sensory testing, including CPT measurements, the electrophysiological measurements, and the autonomic nerve system function tests in the two groups. Significant differences were found in all the above measurements when groups 2 and 3 were compared with diabetic patients without neuropathy (group 1). When all diabetic patients were considered as one group, significant correlations were found between CPT and the other peripheral nerve function assessments. In particular, peroneal nerve motor conduction velocity correlated with CPT at 2 kHz (r = -0.48, P < 0.001) and vibration perception threshold (r = -0.50, P < 0.001). CONCLUSIONS: We conclude that no difference could be found in the function of small and large nerve fibers between painful and painless diabetic neuropathy using conventional tests currently used. The CPT evaluation failed to quantify painful symptoms, but it compared favorably with other quantitative sensory tests in quantifying peripheral neuropathy.