A new diagnostic method for detecting neuropathic diabetic foot by photo-plethysmography

Although nerve conduction velocity (NCV) has been routinely used in diabetic clinics to diagnose diabetic neuropathy, some patients experience considerable pain as a result of the strong electrical stimuli applied, and the method takes about half an hour. It is known that blood flow to the toes is increased in diabetic neuropathy while that to the fingers is little affected. Therefore, the blood flow ratio of the toes to the fingers is suggested as a new diagnostic parameter in diabetic neuropathy by simple photo-plethysmography (PPG). Subjects were allocated to these three groups by NCV tests. There were no significant differences in PPG blood flow ratio between the control group and the diabetic nonneuropathic group (left: p=0.093, right: p=0.888). However, the ratio in the diabetic neuropathic group was significantly higher than in the diabetic nonneuropathic group (left: p=0.000, right: p=0.007) and in the control group (left: p=0.001, right: p=0.000). The threshold ratios between the control and neuropathic group were calculated to be 0.53 for the right side by LMS (least mean square) with a sensitivity and specificity of 72.7% and 71.8%, respectively.