Photobiomodulation for Diabetic Peripheral Neuropathy

This study is a randomized, double-blind, sham-controlled clinical trial. Participants will be enrolled from Move Better Clinic and Madinah Teaching Hospital in Faisalabad, Pakistan.

Randomization and allocation concealment: Eligible participants will be randomly assigned in a 1:1 ratio to either the photobiomodulation therapy group or the sham laser group. Randomization will be performed using a computer-generated random number table. Allocation will be concealed in sequentially numbered, opaque, sealed envelopes that will be opened only after baseline assessment.

Blinding: Participants will be blinded to their group assignment because both groups will undergo the same procedure with the same device; only the experimental group will receive active laser. Outcome assessments will be performed by a physiotherapist who remains blinded to group assignment. The therapist delivering the intervention cannot be blinded, but all data entry and statistical analysis will be performed using coded group identifiers.

Sample size calculation: Sample size of 36 participants (18 per group) was calculated using Rao Software based on a previous study by Suganthirababu et al. (2018), assuming a power of 80% and alpha of 0.05.

Statistical analysis: Data will be analyzed using IBM SPSS software. Normality of data distribution will be tested using the Shapiro-Wilk test. For normally distributed data, within-group differences will be analyzed using paired t-tests, and between-group differences will be analyzed using independent t-tests. For non-normally distributed data, appropriate non-parametric tests (Wilcoxon signed-rank and Mann-Whitney U) will be used. A p-value less than 0.05 will be considered statistically significant.

• Photobiomodulation Therapy (Device): Photobiomodulation therapy (PBMT) was delivered using an infrared light therapy device with 3 x 808 nm and 12 x 650 nm multi-speed modes with pulse function. The device parameters were: wavelength of 900 nm, power of 25W, and frequency of 1000 Hz in pulse mode. The therapy was applied to the dorsum and plantar surface of the foot for 9 minutes per session. Treatment was administered every other day for 2 weeks, resulting in a total of 7 sessions per participant. The intervention was delivered by a trained physiotherapist in a clinical setting at MoveBetter Clinic, Faisalabad, Pakistan. Participants remained in a comfortable seated position with the foot exposed during treatment. Safety goggles were provided to both the participant and the therapist.
• Sham Laser Therapy (Device): Sham laser therapy was delivered using the same infrared light therapy device as the active treatment, with the laser deactivated. The device was positioned and handled identically to the active treatment, and the same auditory signals were produced to maintain blinding of participants. The same procedure was followed: application to the dorsum and plantar surface of the foot for 9 minutes per session, every other day for 2 weeks (total of 7 sessions). Participants were unaware of their group assignment throughout the study period. The sham intervention was delivered by the same trained physiotherapist in the same clinical setting at MoveBetter Clinic, Faisalabad, Pakistan.

Primary outcomes

• Change in Pain Intensity [Baseline and Week 2 (post-intervention)]: Pain intensity was measured using the Numeric Pain Rating Scale (NPRS), an 11-point scale ranging from 0 (no pain) to 10 (worst possible pain). Participants were asked to rate their current level of foot pain at each assessment point. Higher scores indicate greater pain intensity. The change from baseline to post-intervention was calculated for each participant.

Secondary outcomes

• Change in Quality of Life [Baseline and Week 2 (post-intervention)]: Quality of life was measured using the SF-36 questionnaire, a 36-item validated instrument assessing physical and mental health across eight domains: physical functioning, role limitations due to physical health, role limitations due to emotional problems, energy/fatigue, emotional well-being, social functioning, pain, and general health. Domain scores range from 0 to 100, with higher scores indicating better quality of life.
• Change in Neuropathic Pain Characteristics [Baseline and Week 2 (post-intervention)]: Neuropathic pain characteristics were assessed using the LANSS (Leeds Assessment of Neuropathic Symptoms and Signs) scale. The LANSS scale includes sensory descriptions and bedside sensory testing (allodynia and altered pin-prick threshold). Total scores range from 0 to 24. Scores of 12 or greater indicate that neuropathic mechanisms are likely contributing to the patient's pain.

Other outcomes

• Change in Neuropathy Screening Status [Baseline only (screening)]: Neuropathy status was assessed using the Michigan Neuropathy Screening Instrument (MNSI), which includes a 15-item questionnaire and a brief physical examination of the feet. This measure was used for screening and descriptive purposes rather than as a primary or secondary efficacy outcome.

Sex: All, ages: 18 Years to any

Inclusion Criteria:

* Diagnosis of type 2 diabetes mellitus
* Diagnosis of diabetic peripheral neuropathy
* Age 18 years or older
* Male and female participants
* Pain duration of 6 months or more
* Numeric Pain Rating Scale (NPRS) score of 3 or greater out of 10 at baseline
* No acute infections at the time of enrollment

Exclusion Criteria:

* Skin lesions, infections, or ulcers in the treatment area
* Severe heart disease or kidney dysfunction
* Mental illness or malignant tumors
* Presence of pacemaker or implanted electrical device
* Chronic alcohol or drug abuse
* Patients unwilling to provide informed consent
* Pregnancy
* Post-surgical cases (heart or brain surgery) within 30 days
* History of stroke