Diabetes Care 31:316-321, 2008 DOI: 10.2337/dc07-1794 © 2008 by the American Diabetes Association
Does Anodyne Light Therapy Improve Peripheral Neuropathy in Diabetes?A double-blind, sham-controlled, randomized trial to evaluate monochromatic infrared photoenergyFrom the Department of Surgery, Texas A&M University Health and Science Center College of Medicine, Scott and White Hospital, Temple, Texas Address correspondence and reprint requests to Lawrence A. Lavery, 703 Highland Spring Ln., Georgetown, TX 78633. E-mail: lklavery{at}yahoo.com
OBJECTIVE—The purpose of this study was to determine the efficacy of anodyne monochromatic infrared photo energy (MIRE) in-home treatments over a 90-day period to improve peripheral sensation and self-reported quality of life in individuals with diabetes. RESEARCH DESIGN AND METHODS—This was a double-blind, randomized, sham-controlled clinical trail. We randomly assigned 69 individuals with diabetes and a vibration perception threshold (VPT) between 20 and 45 V to two treatment groups: active or sham treatment. Sixty patients (120 limbs) completed the study. Anodyne units were used at home every day for 40 min for 90 days. We evaluated nerve conduction velocities, VPT, Semmes-Weinstein monofilaments (SWM) (4-, 10-, 26-, and 60-g monofilaments), the Michigan Neuropathy Screening Instrument (MNSI), a 10-cm visual analog pain scale, and a neuropathy-specific quality of life instrument. We used a nested repeated-measures multiple ANOVA design. Two sites (great toe and fifth metatarsal) were tested on both the left and right feet of each patient, so two feet were nested within each patient and two sites were nested within each foot. To analyze the ordinal SWM scores, we used a nonparametric factorial analysis for longitudinal data. RESULTS—There were no significant differences in measures for quality of life, MNSI, VPT, SWM, or nerve conduction velocities in active or sham treatment groups (P > 0.05). CONCLUSIONS—Anodyne MIRE therapy was no more effective than sham therapy in the treatment of sensory neuropathy in individuals with diabetes.
Abbreviations: MIRE, monochromatic infrared energy MNSI, Michigan Neuropathy Screening Instrument NeuroQoL, neuropathy-specific quality of life instrument RCT, randomized clinical trial SWM, Semmes-Weinstein monofilament VPT, vibration perception threshold
Monochromatic infrared energy (MIRE) has been suggested to improve diabetic sensory neuropathy and even to prevent foot ulcers (1–7). However, the results of clinical studies are mixed. In a randomized clinical trial (RCT) by Clifft et al. (8), MIRE did not provide improvement in peripheral sensation compared with sham treatment. In contrast, RCTs by Leonard et al. (4) and Arnall et al. (6) reported a significant improvement in peripheral sensation with MIRE. In all three studies one foot was randomly assigned to receive active therapy and one to receive sham therapy. In all three studies Semmes-Weinstein monofilament (SWM) testing was used to evaluate the primary clinical outcomes. Leonard et al. (4) randomly assigned extremities of 27 patients to receive active or sham MIRE in a 2-week study. Leonard et al. reported significant improvements in peripheral sensation with SWMs, the Michigan Neuropathy Screening Instrument (MNSI), pain, and self-reported balance impairment in a subset of patients with "less severe" neuropathy, whereas patients with severe neuropathy did not improve. Arnall et al. (6) used a similar approach and randomly assigned extremities of 22 patients to active or sham therapy for 8 weeks. Arnall et al. reported improved sensation with SWMs but not with vibration perception threshold (VPT) testing. We planned a randomized clinical study to determine the efficacy of anodyne MIRE therapy in improving diabetic peripheral sensory neuropathy. Our hypothesis was that MIRE therapy would improve measures of peripheral sensation compared with sham therapy.
This study was conducted as a double-blind, sham-controlled RCT to determine the efficacy of treatments using anodyne MIRE therapy. The study was approved by the hospital institutional review board, and informed consent was obtained before enrollment. We randomly assigned 69 subjects of whom 60 (120 limbs) completed the 3-month evaluation period: 33 active therapy patients and 27 sham control subjects. We collected patient information regarding age, sex, duration of diabetes, and glycated hemoglobin at baseline and at the conclusion of the study.
Inclusion criteria for the study were as follows: subjects with diabetes who were mentally competent and able to understand and comply with the study, had a VPT
Monochromatic infrared photoenergy therapy
Sensory evaluation We evaluated VPT with the VPT testing instrument as described by Lavery and Young and colleagues (9,10). Measurements were taken at the distal aspect of the great toe and the fifth metatarsal head. The amplitude of vibration was read as a continuous variable in volts on a 0–100 scale. Both monofilament testing and VPT testing were performed with subjects in a reclined sitting position. Both tests were demonstrated on the upper extremity, and the subjects were allowed to visualize the testing process. The subjects were then asked to close their eyes for the lower extremity testing procedures. The subjects responded by saying "yes" when they felt the monofilament and then were asked to correctly identify the site at which they felt the monofilament. If the patient could not identify the site correctly, the test was recorded as a negative response. We evaluated nerve conduction velocities in the tibial nerve and superficial peroneal nerve of each subject with the NC-Stat nerve conduction system on the right foot only (11). Subjects were not included in the analysis if they had unobtainable tibial or peroneal nerve responses.
Neuropathy quality of life instrument
Statistical analysis Initially, descriptive statistics were generated for all variables. To test whether the treatment groups were statistically similar, age and duration of diabetes were compared by treatment, sex, and medication regimen using a multiple ANOVA statistical framework. In addition, a cross-tabulation of the counts of patients by sex, medication, and treatment was analyzed using a log-linear model. The VPT scores, continuous variables measured on at least a ratio scale, were analyzed using a nested repeated-measures design via the MIXED procedure in SPSS (version 14; SPSS, Chicago, IL). Two sites (great toe and fifth metatarsal) were tested on both the left and right feet of each patient, so for the experimental design, the two feet were nested within each patient and two sites were nested within each foot. Other variables that were or could be feasibly treated as continuous variables, including glycated hemoglobin, nerve conduction velocities (several measures for both peroneal and tibial nerves), visual analog scale pain scores, MNSI scores, and NeuroQoL scores, were evaluated using repeated-measures ANOVA via the SPSS GLM procedure. Initially, repeated-measures tests were run with treatment group as a factor and also with continuous covariates (age and duration of diabetes) and categorical factors (sex and medication type). However, because none of these added factors were significant, a single-factor repeated-measures design was used with just one factor: treatment group. The four monofilaments provided at most a five-level ranking of neuropathy. To analyze the ordinal SWM scores, a nonparametric factorial analysis for longitudinal data was used (14,15). The NeuroQoL survey has pairs of related questions: one on a five-point scale for degree or severity and one on a three-point scale of importance. These five- and three-point scale values were multiplied together, forming a composite score. The paired questions were grouped into five categories (Table 2), and each category had a question on the overall importance of that category. A composite category score was created by multiplying the sum of individual category scores by the category importance score, providing an approximately continuous measure that could be analyzed by repeated-measures ANOVA.
In all of the statistical tests, the main focus was to examine whether there was a treatment-time interaction. The treatment-time interaction looks at four effect sizes: treatment at baseline, treatment after 3 months, sham at baseline, and sham after 3 months. It tests whether there is a change in the effects of the treatment group over time compared with the sham group over time. If there was a significant treatment-time interaction, differences in the baseline and ending marginal effects were examined to determine whether the sham or anodyne treatments were associated with the result.
We screened 174 subjects. Sixty-nine subjects met the inclusion and exclusion criteria and were randomly assigned in the study. Sixty subjects (120 limbs) completed the 90-day evaluation period. There were 33 completers in the anodyne MIRE treatment arm and 27 in the sham treatment arm. One study-related adverse event was reported: one subject developed a small wound on his lower leg that healed without incident. Of the nine noncompleters, one had a myocardial infarction, one could not attend visits because of work, and the remainder withdrew without any additional comment. Demographics were similar among the active and sham groups at baseline (Table 1). There were no statistically significant changes in SWM, VPT, nerve conduction velocity, MNSI, visual analog scale pain (Table 1), or NeuroQoL scores (Table 2) for active compared with sham therapy. The ordinal results for the SWM tests were analyzed using a nonparametric factorial design for longitudinal data (Table 3). The effect size is based on an integral of the product of functions derived from empirical distribution functions of the overall or marginal distributions of the ordinal data (14,15). Overall, there was no statistical evidence that the anodyne treatment was effective in improving sensory perception compared with the sham treatment. Not only was there no clear benefit from the treatment, but there also was a large placebo effect in which sham therapy showed double the number of improvements in effect size compared with the anodyne treatment.
We used the NeuroQoL to evaluate self-reported functional status (Table 2). For each category the sham results showed a larger increase than that for the anodyne treatment. There was one statistically significant treatment-time interaction, "Limited home and leisure activities," but it was significant because the sham group improvement was much greater than that for the anodyne group. To assess balance we used two questions from the NeuroQoL that evaluate unsteadiness when standing and walking (Table 1). There was a significant improvement in self-reported unsteadiness with walking in the sham treatment group (P = 0.05). To evaluate pain we used a 10-cm visual analog pain scale and the NeuroQoL (Table 2). Neither demonstrated any significant change during the treatment period.
The results of this study demonstrate that anodyne MIRE therapy provided no more improvement in peripheral sensation, balance, pain, or quality of life than sham therapy. In our study the daily treatment was more frequent and the 90-day evaluation period was longer than those in previous studies. We used several objective and subjective measures of sensory neuropathy, and none of them showed a significant improvement after 90 days of therapy compared with sham treatment. Our results are similar to the RCT reported by Clifft et al. (8). An evaluation of the data from Leonard et al. (6) and Arnall et al. (4) suggests that there was probably not an overall improvement in sensory neuropathy despite their stated conclusions. There were several classic errors in analysis. First, Leonard et al. did not perform an ITT analysis, as the data from the entire study population were not included in the analysis or reported in the article. Instead, they separately evaluated subgroups with moderate and severe neuropathy. It seems very likely that there would not be a significant effect if the entire patient population had been included in the analysis. Second, the analysis used was not appropriate in the studies of Arnall et al. and Leonard et al. The Semmes Weinstein data are count data, and the authors used tests for continuous data in their analysis. Third, both Arnall et al. and Leonard et al. failed to provide analysis comparing the interaction of how patients conditions changed over time for sham and active therapy. An examination of the data suggests that whereas there was a significant marginal improvement, there was not a significant change over time between the active and sham treatments. Both studies separately compared means at the beginning and end of the study via a t test for the active and sham treatments and then compared the P values from these separate tests. This results in what is called a Simpson's paradox: whereas one of the marginal results is significant, comparisons of treatment differences over time are not.
Placebo effect One of the main limitations in evaluating neuropathy is the accuracy and reliability of the tools for longitudinal testing. The SWM was the primary instrument used to assess neuropathy in the RCTs of Leonard et al. (6), Arnall et al. (4), and Clifft et al. (8) and in several uncontrolled studies. Even new monofilaments have considerable variation in accuracy and durability with significant reduction of loading force after repetitive loading (16–19). Our study as well as the study by Clifft et al. used several "levels" of SWMs. In the RCT of Clifft et al., a new set of SWMs from North Coast Medical was used at the beginning of the study (8). However, in the study by Leonard et al. no information was provided about the manufacturer, previous use, or replacement of SWMs. We used 4-, 10-, 26-, and 60-g monofilaments and replaced them after evaluating every 10 patients in an effort to reduce SWM wear and increase reproducibility of results. In addition, our study and that of Arnall et al. used VPT testing. VPT is a well-accepted device for quantitative sensory testing (20); however, large coefficients of variation have been identified in several studies when individuals with diabetes and elderly individuals were tested (21,22). In addition, our study may have been underpowered to determine subtle changes in neuropathy with therapy. However, previous studies reported positive results with fewer subjects who received fewer treatments with shorter evaluation periods than in our RCT. We did not see any strong trends that MIRE was different from sham therapy, and, in fact, there were instances in which sham therapy was superior to MIRE therapy.
Pain and balance The result of this study should be generalizable to individuals with diabetes with "loss of protective sensation." In normal practice MIRE therapy is initially provided three times a week in a clinical setting. Many patients, will subsequently use the device at home, so our daily "dosing" regimen and period of evaluation reflects long-term use patterns. At present there is no compelling evidence that MIRE can improve loss of protective sensation such that high-risk people with diabetes have a decreased risk of foot complications. Our results did not show a change in self-reported balance, pain, quality of life, electrodiagnostic studies, or clinical sensory measures. MIRE is no more effective than placebo or sham therapy in improving peripheral sensation, balance, and pain in individuals with diabetes.
Published ahead of print at http://care.diabetesjournals.org on 31 October 2007. DOI: 10.2337/dc07-1794. Clinical trial reg. no. NCT00120341, clinicaltrials.gov. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C Section 1734 solely to indicate this fact. Received for publication September 11, 2007. Accepted for publication October 23, 2007.
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