A Prospective Study of Diabetic Peripheral Neuropathy (DPN)

By Allan Gardiner, PhotoMed Technologies, Founder


Diabetes makes headlines for the 29 million Americans who are affected by a progression of associated disorders, limited mobility, neuropathies, wounds, and amputations. This small study asked whether PhotoMed's therapy could help.

For some, invasive interventions adequately mask pain and other symptoms. For others, pain and non-healing wounds consume their days and pocketbooks.

PhotoMed sponsored a prospective open-label clinical study to evaluate the efficacy of variable wavelength light for reducing diabetes-related pain. The study tested PhotoMed's hardware and software under actual clinical trial conditions.

PhotoMed's team also designed the study to examine questions that may affect future photobiomodulation (previously called laser therapy or LLLT) studies. Our preliminary findings expand the utility of photobiomodulation therapy (PBMT) to wavelengths throughout the visible spectrum including those below 600nm. (Most PBMT research examines wavelengths of 600nm and longer.)

We tested our hypothesis that therapy applied to the skin at wavelengths below 600nm would be sufficient to prompt benefit in subjects with diabetic neuropathy. Wavelength and subject selection simplified our hypothesis testing:


Study participants were a series of 29 subjects of African American descent. On average, study volunteers had been experiencing diabetic peripheral neuropathy (DPN)-related pain for more than 3 years prior to the study.  More than one-third of the patients were using opioid analgesics for pain control upon entry into the study. No changes in medications were requested during the treatment period.  At the end of 2-3 weeks of treatment, patients again provided ratings of their current pain and impairment. 


Methods (Abbreviated):

29 subjects, 95% of African American descent, were consented and enrolled in an IRB-reviewed study. Subjects provided standardized ratings of pain and impairment in daily activities. Narratives and medication information were collected in a database for later examination.

Patients then participated in six phototherapy visits with PhotoMed's therapy using only blue-green-yellow wavelengths (400-590nm) over the course of 2-3 weeks. See Figure 1. One open-label treatment was inactive during one of the first two to test randomization. The test provided a delayed-entry style comparison of active vs. inactive treatments delivered during the first visit.

Figure 1 - PhotoMed's Rapid Discovery System™ controlled the light output and data collection. Wavelengths from 400 to 600nm were applied. Red and infrared wavelengths were excluded to reduce penetration through the skin.


Administration of treatments was facilitated by on-screen prompting visible only to the technician. The next locations to place the two applicators was shown graphically with a count-down to the automated start of the next treatment. The treatment sequence and timing was the same for all subjects. The treatment locations were standardized by reference to acupuncture points. No other meaning was considered for the use of acupuncture point locations.

Five treatments were applied with wavelengths, times, frequencies, and locations as shown in Figure 2.


Figure 2 - Prospective treatment locations were identified by acupuncture point designations for the technician's convenience. The settings anticipated several common sources of pain and impairment. The treatments were delivered on a computer-timed schedule.



Testing of the hardware, software, and PhotoMed's experimental therapy exceeded expectations. Narratives and questionnaires supported PhotoMed's hypothesis that therapy applied to the skin at wavelengths below 600nm was sufficient to prompt benefit in subjects with diabetic neuropathy. Consistent with prior testing, dark skin color does not appear to limit effectiveness of PhotoMed's experimental therapy.

The McGill Short Form questionnaire provided a validated means of comparing pain levels at the beginning and end of the study. See Figure 3. The questionnaire consisted of 11 questions that address different sensory experiences, 4 questions about how the pain affects the person, and a 101-point numerical rating scale.


Figure 3 - On a McGill Short Form scale, 21 of 29 subjects reported at least 50% less pain by the end of the study. Some subjects reported multiple sources of pain that improved during the study. One-third of the subjects were taking opioid analgesics for their pain.


Two aspects of pain in people with diabetic neuropathy appeared to be particularly noticeable. Sharp and tingling pain were frequently scored in the McGill forms at the beginning of the study. See Figure 4. One-third of subjects were taking opioid analgesics for their pain. Further studies might identify the effectiveness of opioids for these types of pain. Some subjects were taking more than six different medications.


Figure 4 - Two sensory aspects of pain from the McGill questionnaire offer insights into the improvement in symptoms. Two-thirds of the subjects initially reported these types of pain. One-third were taking opioid analgesics.


The statistician was pleased with receiving a database with entries for all data. PhotoMed's software prompted the technician to ensure that all questions answered for the McGill and similarly scored questionnaires. The results are shown in Table 1.


Table 1 - Tabular results from McGill Short Form and other questionnaires.



Preliminary findings from the study confirm that a community experiencing high rates of DPN can benefit from PhotoMed's therapy. The outcomes support PhotoMed's hypothesis that therapy applied to the skin at wavelengths below 600nm was sufficient to prompt benefit in subjects with diabetic neuropathy

Additionally, the use of wavelengths selected for low penetration through dark skin suggests that neither penetration nor the presence of red or infrared wavelengths are requirements for effective photobiomodulation.

Note that no differences in responses relative to skin color have been found in PhotoMed's patient-centered studies.


Further investigation of this treatment protocol and PhotoMed's personalized protocols in more rigorous placebo-controlled studies appears to be warranted.


Notes from other PhotoMed sponsored studies

In patient-centered studies, no difference in effects have been noted as a result of skin color, race, or ethnicity.

Updated: July 10, 2018   


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