Cold-loaded pain sensation test and current perception threshold for evaluating diabetic neuropathy

Objective We previously designed and reported a simple new method (the cold-loaded pain sensation test) for quantitative evaluation of the function of small nerve fibers. In the study reported here, we investigated the clinical usefulness of this test to evaluate diabetic neuropathy by comparison with a device for quantitative measurement of the neuroselective current perception threshold (CPT). Patients and methods We evaluated 68 diabetic patients without cerebrovascular disease. After cooling the test site, the recovery time (RT) required for pain sensation to return to an equivalent level to that on the noncooled side was evaluated. The rapid screening mode was employed to measure CPT. Results RT measured at the great toe (77.8 ± 43.2 s) was significantly longer than that measured at the medial malleolus (53.8 ± 30.0 s) ( p < 0.01). Although the A delta-CPT level measured at the medial malleolus was not correlated with that of the great toe ( r = 0.23, p = 0.06), the C-fiber (C)-CPT level measured at the medial malleolus was positively correlated with that of the great toe ( r = 0.60, p < 0.01). In addition, the A delta-CPT level was positively correlated with the RT at the great toe ( r = 0.52, p < 0.01). When multiple regression analysis was done using the A delta-CPT or C-CPT level as the dependent variable, and with RT at the great toe and medial malleolus, age, diabetes duration, and glycated hemoglobin (HbA 1c ) as explanatory variables, RT at the great toe was a determinant of the A delta-CPT or C-CPT level at the great toe. Conclusion Findings in this study suggest that impairment of small nerve fibers is more severe distally in patients with diabetic neuropathy. In addition, the validity of the cold-loaded pain-sensation test to evaluate small-nerve-fiber impairment was demonstrated.