Effect of Monochromatic Infrared Energy on Quality of Life and Intraepidermal Nerve Fiber Density in Painful Diabetic Neuropathy: A Randomized, Sham Control Study

Background: Monochromatic infrared energy (MIRE) has evoked mixed results for symptomatic relief of painful diabetic peripheral neuropathy (DPN). However, intraepidermal nerve-fiber density (IENFD) the gold standard for small-fiber neuropathy has not been evaluated. Objective: We assessed the IENFD, pain symptoms and quality of life (QoL) with MIRE therapy compared to placebo in painful DPN. Material and Methods: Participants with type 2 diabetes and painful DPN were randomized to receive MIRE or sham therapy dosed thrice a week for 12 weeks. Quantitative assessment of IENFD was performed from 3 mm skin punch-biopsy specimens at baseline and after 12 weeks. We also assessed the QoL with Norfolk QOL, symptom severity with visual analogue scale (VAS), and neuropathy assessment with Michigan neuropathy severity instrument and neuropathy disability score. Results: Thirty-eight participants were enrolled and 30 completed the study protocol. The mean age of participants in MIRE cohort was 59.1 +/- 9.2 years, duration of diabetes 12.9 +/- 3.1 years, and symptom duration of 3.9 +/- 3.7 months. The mean IENFD was 0.90 +/- 0.73/mm(2) (P < 0.01) and 1.71 +/- 1.11/mm(2) in the MIRE cohort and 0.60 +/- 0.89/mm(2) and 2.17 +/- 0.98/mm(2) (P < 0.01) in sham cohort at baseline and after 3 months. The median decline in VAS was 5.1 (4.0-7.6) and 3.0 (0.4-5.6) points (intergroup difference, P = 0.01); and an increase in Norfolk QoL-DN by 15 (11-18) and 4 (4-14.2) points (intergroup difference, P = 0.021) in MIRE and sham cohort, respectively after 3 months. Conclusions: MIRE therapy does not increase IENFD over short-term usage. However, MIRE therapy provides symptomatic benefit and improves QoL in patients with painful DPN.