Diabetes is a very common cause of peripheral neuropathy, and there is no optimal intervention universally accepted by clinicians. Monochromatic infrared photo energy is a relatively new modality used in the United States for reducing pain and increasing circulation. This study investigated the effects of monochromatic infrared photo energy on reducing pain, improving sensation, and increasing balance in patients with diabetic peripheral neuropathy. Thirty-five patients with diabetic peripheral neuropathy completed the program and were randomly assigned into two groups. Group 1 (experimental,
Diabetic peripheral neuropathy (DPN) is a common progressive complication of diabetes mellitus [
Patients with early DPN usually experience pain that worsens at night: perceived numbness, and a tingling sensation in the feet and hands. Patients may show reduced ability to detect temperature changes and/or pressure in the feet in advanced stages, and these symptoms are associated with postural instability, loss of leg and foot strength, and reduced proprioceptive thresholds in foot inversion, eversion, plantar flexion, and dorsiflexion [
Although there is no definitive intervention for the treatment of DPN, the mainstay generally hinges on rigorous glycemic control and reduction of pain and paresthesia by either topical or systemic means [
Various types of electrotherapy, such as transcutaneous electrical nerve stimulation (TENS), pulsed electromagnetic fields (PEMF), static magnetic field therapy, external muscle stimulation, and frequency-modulated electromagnetic neural stimulation, have been reported to decrease pain and increase circulation. However, results of the studies describing the effects of these modalities on peripheral neuropathy remain controversial, and randomized-controlled studies with larger sample sizes and long followup periods are needed in order to better elucidate the efficacy of these modalities. And, although electrotherapy modalities may help decrease pain [
Monochromatic infrared photo energy (MIPE) represents another approach to the management of DPN. MIPE was cleared by the United States Food and Drug Administration in 1994 for increasing circulation and reducing pain. MIPE at a wavelength of 890 nm is produced by an array of 60 gallium aluminum arsenide light-emitting diodes located on flexible pads and the near infrared photo energy is delivered in a noninvasive, drug-free manner. The diode array must be placed in direct contact with the target skin, as MIPE energizes cells in the epidermis and the most superficial portion of the dermis, thereby warming the skin. The 890 nm photo energy penetrates the skin enough to be absorbed by hemoglobin in the rete capillary loops in the papillary dermis, rather than just water in the more superficial layers [
A few studies have investigated the efficacy of MIPE at reducing pain, improving foot sensation, and increasing balance in patients with peripheral neuropathy. However, we believe that the results of these previous studies were adversely influenced by methodological limitations that threatened the authors’ conclusions, including the lack of a control group [
A randomized controlled study was undertaken with participants randomly assigned to one of two intervention groups: group 1 received MIPE, therapeutic exercises, and balance training, whereas the participants in group 2 received therapeutic exercises and balance training without MIPE. The duration of intervention was 4 weeks per participant, and each participant was scheduled to undergo 3 therapy sessions per week. Measurements were taken at baseline and after end of treatment (4 weeks).
Participants were recruited from an outpatient rehabilitation setting and were treated between December 2010 and April 2011. To be included in the study, participants had to have diabetes mellitus, either type 1 or type 2. The maximum allowable HbA1c level required for inclusions was ≤7%. Furthermore, to be included, participants’ drug regimen, as well as interventions to promote blood flow in the lower extremities, had to remain stable for one month prior to commencement of the investigation, and throughout the course of the investigation once the study commenced. A 1-month washout period was also required for any participant taking any drug aimed at promoting lower extremity arterial perfusion. Still further, to be included, participants had to have DPN as evidenced by insensitivity to the 5.07 SWM on at least 2 of 5 (great toe, fourth toe, and 3 of the 5 metatarsal heads) plantar surfaces of both feet.
The Berg balance score (BBS) [
Participants who met the inclusion criteria were randomly assigned to one of the two treatment groups. The randomization process involved blank folders numbered from 1 to 100 and containing hidden codes for group assignment, and a random-number generator had determined the codes. When a participant was eligible and gave consent to participate, the investigator drew the next folder from the file, which determined treatment allocation. Each participant was then tested using a visual analogue pain rating scale, the 5.07 SWM, and the BBS.
An independent investigator, blinded to group allocation, conducted the testing procedures. This investigator assessed participants in both groups at both the initial and final sessions. After initial testing, participants began the intervention on the same day. A licensed physical therapist performed all interventions with the participants from both groups. All participants underwent 3 sessions per week for 4 weeks. A coworker helped procure data used in this investigation by taking measurements following the study protocol, although that individual did not devise the study or participate in the analysis or interpretation of the data.
MIPE intervention was administered using the Anodyne Therapy System, model 480 (Anodyne Therapy, LLC, Tampa, FL). The device consisted of a base power unit and 8 therapy pads, each containing 60 gallium aluminum arsenide diodes. The area of light-emitting diodes per therapy pad was 22.5 cm2, yielding a total intervention area of 180 cm2. The diodes delivered MIPE pulsed at 292 Hz at a wavelength of 890 nm and provided an energy density of 62.4 Joules/cm2 [
Participants in group 2 underwent only the physical therapy that was the same regimen undertaken by the participants in group 1. The physical therapy program included static and dynamic balance retraining, as well as active lower extremity strengthening (hip extensors, hip abductors, hip adductors, quadriceps, ankle dorsiflexors) and stretching of the hip, knee, and ankle flexor musculature. Participants in both groups were educated as to the rationale for the therapy, and they received verbal and written instructions related to the proper method of exercise, and they demonstrated to the treating therapist their ability to properly perform the prescribed exercises. All participants were instructed to exercise at home on the days that they did not go to the clinic for supervised intervention, and the home program was monitored by asking the participants to record exercise using weekly self-reported exercise logs.
The 10 cm visual analogue pain rating scale was used to measure neuropathic pain because it is reliable and provides a valid assessment of pain intensity [
Balance was assessed using the BBS, which has been shown to be reliable (intraclass interrater reliability correlation coefficient =.99) [
Data analysis was performed using SPSS for Windows, version 18.0. Data were analyzed using the analysis of covariance (ANCOVA), with the pretest (baseline) scores for the outcomes or interest as the covariates. The ANCOVA was used to take into account the baseline measurements for each patient. When baseline information is available, this provides a more precise estimate of the treatment effect than either raw outcomes or change scores [
A total of 41 patients met the inclusion criteria, including 18 (43.9%) males and 23 (56.1%) females. Of these, 10 (24.39%) had type 1 diabetes mellitus, and 31 (75.61%) had type 2. Random allocation placed 21 (51.22%) into group 1 (to receive MIPE + training) and 20 (48.78%) into group 2 (training only). In group 1 (
The loss of participants to follow up was associated with difficulties primarily related to scheduling the intervention sessions in both groups (2 (9.52%) of 21 in the MIPE group, and 2 (10%) of 20 in the training only group), and for scheduling conflicts in 2 other participants (the 1 (4.76%) who developed CHF in the MIPE group and the 1 (5%) lost for unknown reasons in the training only group). For these reasons, a total of 35 participants, 18 (51.43%) in the MIPE group and 17 (48.57%) in the training only group, were included in the final analysis.
Baseline demographic characteristics describing the participants who completed the investigation are depicted in Table
Physical characteristics of the participants (number = 35 participants)*.
Variable | Group 1—training + MIPE |
Group 2—training only ( |
|
---|---|---|---|
Age (years) | 62.03 ± 11.01 | 59.4 ± 8.51 | |
Height (cm) | 161.34 ± 6.21 | 158.23 ± 5.82 | >.05 |
Body weight (kg) | 68.32 ± 10.19 | 73.1 ± 9.61 | |
Body mass index (kg/m2) | 24.25 ± 7.21 | 21.8 ± 4.14 |
*Values are mean ± standard deviation.
†Independent sample
Outcomes at baseline and 4 weeks, by intervention group (number = 35 participants)*.
Outcome | Group 1—training + MIPE |
Group 2—training only ( |
|
---|---|---|---|
10-cm analogue pain scale | Baseline | 6.2 ± 2.1 | 7.3 ± 1.1 |
4 weeks | 3.9 ± 1.8 | 5.1 ± 2.3 | |
|
≤.05 | ||
Monofilament sensation¶ | Baseline | 7.2 ± 1.8 | 8.3 ± 0.9 |
4 weeks | 1.4 ± 2.1 | 7.2 ± 1.3 | |
|
.025 | .06 | |
Berg balance score§ | Baseline | 31 ± 9.27 | 28.58 ± 10.16 |
4 weeks | 47.61 ± 10.16 | 32.52 ± 9.54 | |
|
≤.05 |
*Values are mean ± standard deviation.
†Dependent sample
¶Possible score ranging from 0 to 10, indicative of the number of separate pedal anatomic sites where 5.07-monofilament touch-pressure was not appreciated by the participant (lower score indicative of more sensation).
§A score of 21–40 indicates balance impairment and a heightened medium risk of falling.
Table
Results of analysis of covariance between the groups at 4 weeks after intervention (number = 35 patients)*.
Outcome | Group 1—training + MIPE |
Group 2—training only ( |
|
|
---|---|---|---|---|
10-cm analogue pain scale | 3.9 ± 1.8 | 5.1 ± 2.3 | 8.16 | .01 |
Monofilament sensation¶ | 1.4 ± 2.1 | 7.2 ± 1.3 | 4.2 | .014 |
Berg balance score§ | 47.61 ± 7.39 | 32.52 ± 9.54 | 12.06 | .0001 |
*Values are mean ± standard deviation.
†Analysis of covariance.
¶Possible score ranging from 0 to 10, indicative of the number of separate pedal anatomic sites where 5.07-monofilament touch-pressure was not appreciated by the participant (lower score indicative of more sensation).
§A score of 21–40 indicates balance impairment and a medium risk of falling.
All of the participants in this investigation showed reduction in pain, increased foot sensation, and increased balance scores, in both intervention groups, although the improvements were statistically significantly greater in the group of participants that received MIPE (Tables
The basic idea of this study was to treat the two groups exactly the same in every detail except one (MIPE). The author examined the two groups to see if the MIPE made a difference between them. The difference between groups was attributed to the MIPE.
Although the exact mechanism by which MIPE improves sensation in the diabetic neuropathic foot is not precisely known, it has been proposed that it leads to increased release of nitric oxide and improved microcirculation for the following reasons Nobel Laureate Robert Furchgott reported that photo energy modulates circulation, and it has been shown that exposure to 890 nm near infrared photo energy promotes increased blood flow for several hours in rats by mediating endothelial nitric oxide synthase [ Photo energy absorbed by hemoglobin increases the amount of nitric oxide in red blood cells, in the form of nitrosothiols, and therefore MIPE is likely to increase vasodilatation secondary to release of nitric oxide [ Diabetic glycosylated hemoglobin binds nitric oxide and inhibits its release from hemoglobin at microcirculatory sites, and MIPE is likely to enable release of nitric oxide from glycosylated hemoglobin [
Since patients with DPN often have concomitant decreased capillary blood flow to tissues of the feet and impaired circulation to the peripheral nerves, it is plausible that improved oxygenation and nutrition related to nitric oxide metabolism related to MIPE could promote nerve growth and reestablish nerve membrane potentials that had been reduced by the hypoxic conditions associated with diabetes [
There has been some research into the efficacy of exercise as it pertains to increasing balance in patients with DPN [
Moreover, Kruse et al. [
There are a number of published articles [
A third report [
A fourth report [
Finally, a sixth published report [
Potential limitations of this particular report include the usual problems associated with patients logging their activities, and other biases related to unmeasured confounders. Loss to follow up was mostly due to scheduling difficulties or taking the time to participate in the study in each group. Therefore, it cannot be argued that participants withdrew due to the interventions. There are a number of potential biases that could threaten the validity or conclusions, and for these reasons we realize that future investigation remains necessary in order to better understand the clinical value of MIPE in the management of DPN.
Perhaps the biggest limitation of this study relates to the fact that the author did not employ sham MIPE, and the improvements in the dependent variables could have been due to the placebo effect. Both groups received therapeutic exercises and balance training which may have influenced the improvement. Moreover, the author did not undertake an explanatory analysis, nor did we take into consideration every independent variable that experienced clinicians may think of as important in regard to the treatment of DPN. For instance, the participants were not asked to change any aspect of diet, exercise, drugs, and the author did not analyze the potential influence of psychoactive drugs and other intrinsic risks for falling. Moreover, the neuropathic pain questionnaire could have been used instead of the visual analogue score to measure neuropathic pain [
Still further, additional research is needed to more precisely identify the role that nitric oxide plays in these outcomes, and whether or not the improvement in sensation, pain, and balance that were observed in this 1-month follows-up study is sustained longterm. Treatment only lasted for 4 weeks which is too short and it is questionable whether improvement would be lasting. It is also recommend comparing MIPE to other photo energy modalities such as laser to establish its superiority over these modalities. Based on the results of this randomized, controlled clinical trial, MIPE may be effective in decreasing pain, restoring sensation, and increasing balance in patients with DPN.
The author declares that there is no conflict of interests.