STRENGTHS AND LIMITATIONS OF THIS STUDY

Use of a multiwavelength light-emitting diode (LED) boot for photobiomodulation (PBM) delivery.

Participants can use the device at home.

Randomised controlled trial design.

Double-blind methodology.

The 60-day follow-up may be insufficient for the determination of the long-term preventive effects of PBM.

Introduction

An estimated 531 million people throughout the world live with diabetes mellitus (DM), which corresponds to 10% of the population between 20 and 79 years of age; this number can reach 643 million by 2030 (International Diabetes Federation, 2021).1

The incidence of diabetic foot ulcer (DFU) in this population can reach 15%, with men three times more likely to develop this condition. Between 19% and 34% of individuals with diabetes will have DFU at some time in life, resulting in up to 26 million cases annually throughout the world, with an incidence rate of 2% a year.2–5 DFU have a 40% recurrence rate in 1 year and a 65% rate in 3 years, and six out of every 1000 affected individuals will suffer annual amputations due to complications.2 4 5 Thus, it is crucial to identify the risks and expand DFU prevention strategies.

The prevention of DFU involves therapeutic education,2 6 the use of adequate footwear,2 6–8 the treatment of risk factors in the feet,6 9–11 supervised practice of physical exercises2 12 13 and adjunct treatments. Photobiomodulation (PBM) is among the adjunct treatments that have been addressed in recent systematic reviews and shown promising results.14 15

A recent systematic review with meta-analysis of 12 controlled clinical trials assessed the use of PBM in the treatment of DFU and showed that patients treated with laser had a 30.9% reduction in the area of the lesions and a 4.65-fold greater likelihood of healing compared with a control group that did not receive PBM. However, the considerable variation in the dosimetric parameters impeded the definition of the ideal dosimetry.14 In a systematic review and meta-analysis on dosimetry in the treatment of DFU, Dos Santos Mendes-Costa et al15 found that the most widely used wavelengths are in the red and near-infrared spectra. The authors also corroborated findings described by Zhou et al14 that the majority of articles did not describe the other parameters, underscoring the need for novel randomised controlled clinical trials for this purpose.

Besides the therapeutic effects of PBM, the preventive effects have drawn the attention of researchers. Systematic reviews have been published with recommendations for their preventive use in cases of oral mucositis,16 complications of COVID-1917 and radiodermatitis.18

This project proposes the assessment of the effect of PBM combined with care and routine outpatient follow-up on the prevention of DFU in patients with moderate to high risk for the development of this condition, with the incidence of ulcers as the primary outcome. In addition to the prevention of infection, ulceration or destruction of tissues of the foot—defining characteristics of DFU—the project will also evaluate peripheral neuropathy (PN), peripheral artery disease (PAD) (which frequently accompany this condition) and quality of life as secondary outcomes.

Methods and analysisStudy design

A randomised, parallel, controlled, double-blind, clinical trial is proposed. The study will be conducted at the Mandaqui Hospital Complex, Sao Paulo, Brazil. The design will follow international recommendations for randomised clinical trials—Standard Protocol Items: Recommendations for Interventional Trials (SPIRIT protocol). The flowchart is shown in table 1.

Table 1

Standard Protocol Items: Recommendations for Interventional Trials flowchart

Selection of sample

Individuals of both sexes between 18 and 75 years of age with type 2 DM (according to the criteria of the American Diabetes Association 2021)1 and at moderate to high risk of developing DFU based on the scale of the International Working Group on Diabetic Foot (International Working Group on Diabetic Foot)19 will participate in the study.

Moderate risk: individuals with PN and PAD or PN and foot deformity or PAD and foot deformity.

High risk: individuals with PN or PAD and a history of foot ulcer, amputation of the lower limbs or end-stage kidney disease.

PN will be considered present if an incorrect answer occurs at any site tested in two of the three applications of the Semmes-Weinstein monofilament test and 128 Hz tuning fork (IWGDF 2019).1 PAD will be considered present in participants classified with Grade 1–3 ischaemia, as recommended by the IWGDF 2019.19

The following will be the exclusion criteria: pregnant women, individuals with type 1 diabetes, those with neuropathy secondary to uncontrolled diseases (hypothyroidism, vitamin B12 deficiency, alcoholism), individuals with an infectious condition at the time of inclusion, those with active ulcers or infectious skin lesions of the legs/feet, those with a history of osteomyelitis, those with Parkinson’s disease, those with a contracture condition, those with signs of severe ischaemia of the lower limbs (Fontaine III and IV—Rutherford 4–6), those with suspicious skin lesions for neoplasms or cutaneous dysplasia in the legs/feet, those with a diagnosis of cancer and those in treatment in the previous 3 months, those with unstable angina, recent acute myocardial infarction, history of severe arrhythmia in the previous 6 months, those with uncompensated chronic obstructive pulmonary disease, those unable to understand the statement of informed consent and those who do not appear for the appointments regularly.

Participants who fail to appear for a treatment or assessment session and present any trophic lesion on the legs or feet or any type of infectious complication (tinea, erysipelas, etc) will not be part of the statistical analysis, as such cases will not be in the expected state for the indication of treatment. However, this data will be described and discussed, as will possible adverse effects.

To boost enrolment, collaboration with healthcare providers will be established to encourage patient referrals. Educational sessions and materials will raise awareness.

The educational material will include instructions on healthy eating, physical activity, blood glucose monitoring, medication adherence, recognition of hypoglycaemia signs, risk reduction strategies, adaptation to special circumstances and proper foot care. The medical records containing participant data will be kept in a secure location within the hospital, and the data will be stored in anonymised spreadsheets.

Informed consent procedures

Participants who consent to take part in the study will sign the informed consent (IC) form (supplementary material) after receiving a comprehensive verbal and written explanation from the principal investigator, noting that they will not receive compensation for participating in the study. The participants will be informed that they can withdraw from the study at any point and for any reason, should they so desire.

Calculation of sample size

For the calculation of the sample size, the main outcome was the incidence of foot ulcer, using data from the study conducted by Suryani et al,20 who investigated the incidence of ulcer after flexibility and resistance exercises in patients at high risk based on the IWGDF classification, observing a statistically significant difference in the experimental group (reduction in incidence compared with the control group). Considering a 5% rate of error, 95% confidence level and minimum incidence of 25% in the experimental group and 68% in the control group, the minimum sample size was determined to be n=54 (27 participants per group). To compensate for a possible 20% dropout rate, the sample will be composed of 64 participants (32 per group).

Experimental groups

The participants will be randomised into two groups:

Control group (n=32), which will receive therapeutic education (nutrition, examination and self-care of feet, and counselling on physical activity). The participants in this group will wear an orthopaedic boot with inert light-emitting diodes (LEDs) and undergo examinations every 30 days.

PBM group (n=32), which will receive therapeutic education (nutrition, examination and self-care of feet and counselling on physical activity). The participants in this group will wear an orthopaedic boot with therapeutic LEDs and undergo examinations every 30 days.

Each participant will treat both feet, respecting the inclusion and exclusion criteria.

Randomisation

A random sequence generating programme (https://www.sealedenvelope.com/) will be used for the random allocation of the participants to the two groups, with randomisation performed in blocks of eight patients. Opaque envelopes will be identified with sequential numbers (1–64) and will contain a card stipulating the group according to the generated order. The envelopes will remain sealed in numeric order in a secure place until the sessions.

Blinding

Allocation concealment will be ensured, as the assessors will not have access to the randomisation list or allocation process of the participants to the groups. Participants will remain unaware of the group to which they are allocated, as they will receive boots for home use. The boots in the control group will simulate treatment by emitting the same sound and incorporating a guiding light in the activation plug. Furthermore, participants will be informed that the boot is equipped with both visible (red) and invisible (infrared) LEDs, and they will be advised that they might not see the light emitted by the device during treatment. The generation of the randomisation sequence and preparation of the envelopes will be performed by a researcher not otherwise involved in the study.

Initial assessment and therapeutic education

All participants who meet the eligibility criteria for the study and sign the statement of informed consent will have their clinical history and demographic data collected, undergo a clinical examination and receive therapeutic education (nutritional advice, examination and self-care of feet and counselling on physical activity). The outcome measures will be administered before and after the interventions.

Clinical examination

Data collection will encompass several anthropometric measurements, including height, weight, body mass index (BMI) and abdominal circumference; these evaluations will be repeated at 30 and 60 days post-intervention. Additionally, comprehensive blood and urine analyses will be conducted to evaluate various biomarkers, including the leukogram, ultra-sensitive C reactive protein, platelet count, ferritin, urea, creatinine, fasting blood glucose, glycated haemoglobin, total cholesterol, high-density lipoprotein (HDL) cholesterol, low-density lipoprotein (LDL) cholesterol, triglycerides, thyroid-stimulating hormone (TSH), vitamin B12, microalbuminuria and serum iron levels. These evaluations will be repeated after 60 days.

The feet will be assessed with participants in both lying down and standing positions. This examination will be repeated at 30 and 60 days.

The following aspects will be verified:

Skin (hydration, coloration, reactive hyperaemia, distribution of hair, skin and nail integrity, and signs of preulceration).

Presence of deformities and areas of abnormal pressure (prominence of metatarsals, bunion, claw toes, callouses, loss of plantar arch and Charcot foot).

Shoes: poorly adjusted or inadequate shoes, lack of shoes, format (adequate or not), material on upper and lower portion (leather or plastic), internal examination with hands (presence of foreign objects, irregularities, folds, lining wear), removal of insoles and examination of possible impressions left by bone deformities.

Hygiene (cutting of toenails, unclean feet, superficial fungal infection and dirty socks);

Physical limitations that can hinder self-care of feet (poor visual acuity, obesity).

Limited joint mobility.

Assessment of peripheral neuropathy

PN will be investigated using the Semmes-Weinstein monofilament test,19 21 22 the assessment of vibratory sensitivity using a 128 Hz tuning fork,19 23 investigation of Achilles reflex19 24 and two scales of signs and symptoms of neuropathy (Neuropathy Symptom Score (NSS) and Neuropathy Disability Score (NDS)),25–28 translated and validated for Brazilian Portuguese.29

Assessment of peripheral artery disease

The assessment of PAD will include cardiovascular history, the assessment of the degree of ischaemia, Doppler ultrasound examination, assessment of claudication and thermography of the feet.6 19 30 Although no diagnostic modality is considered ideal when used alone, the diagnosis of PAD is less likely when the ankle-brachial index (ABI) is 0.9–1.3, the toe brachial index (TBi) is ≥0.75 and the Doppler wave of foot pulse is triphasic.19

The degree of ischaemia (1–3, as recommended by the IWGDF 2019)19 will be determined through palpation of the foot pulse and posterior tibial pulse, measurement of systolic pressure of the ankle, determination of ABI, measurement of systolic pressure of the hallux and determination of TBI.19 31 32 The two lower limbs of each patient will be considered independent. Thus, each individual will contribute two ABIs and two TBIs.

Vascular ultrasound will include peak systolic velocity, the resistance index and the wave pattern of distal segments of the anterior and posterior tibial arteries and fibular artery.

Claudication will be assessed using the Edinburgh Claudication Questionnaire33–35 validated for Brazilian Portuguese by Makdisse et al.36

To obtain thermographic images of the feet, the participants will be instructed to wash the lower limbs or bathe/shower within 2 hours prior to the examination, not to practice physical activity on the day of the examination, and not to put lotions or any other substance on the lower limbs.9 37 The room in which the images are captured will be climatised, with the temperature stabilised between 21 and 23°C.9 After the removal of shoes and socks, the participants will remain in the supine position with a cushion under the legs without ankle support, holding the legs slightly separated for a minimum of 15 min. The images will be captured by a hypersensitive infrared sensor (18 mm; resolution: 320×240 pixels) (Flir T420, Flir Brasil, Sorocaba, São Paulo, Brazil) on a tripod at 150 cm from the soles of the feet. A 15 cm ruler will be included in each image. The images will be analysed and compared using software adequate for the analyses of this study.

Assessment of quality of life

Quality of life will be assessed using the Diabetes 21 Questionnaire, which is the short form of the Diabetes 39 Questionnaire38 39 validated by Sousa et al.40

All participants will receive therapeutic education at the initial assessment and every 30 days. A foot care manual will be developed by the research team based on the IWGDF guidelines.19

InterventionsControl group

The participants allocated to the control group will receive counselling on self-care and simulated PBM. Simulated treatment will be performed using a device identical to that used in the active PBM group in the form of a boot but without the emission of therapeutic light. The participants will receive the same instructions on use. At the end of the study, the participants in the control group will receive active PBM if it proves effective on the outcomes of interest.

Photobiomodulation group

The participants allocated to the PBM group will receive counselling on self-care and active PBM using a device in boot form (figure 1) assembled with LED plates (model Sportllux, Cosmedical, Mauá, SP, Brazil) that together yield a total of 1344 LEDs:

504 located on the sides of the boot with a wavelength of 660 nm (power: 28.5 mW; programmed for the emission of 10 J of radiant energy for the 6 min period).

504 also located on the sides of the boot with a wavelength of 850 nm (power: 23 mW; programmed for the emission of 8 J of radiant energy for the 6 min period).

168 located on the base of the boot with a wavelength of 660 nm (power: 28.5 mW; programmed for the emission of 10 J of radiant energy for the 6 min period).

168 also located on the base of the boot with a wavelength of 850 nm (power: 23 mW; programmed for the emission of 8 J of radiant energy for the 6 min period).

Figure 1

PBM device in boot form. (A) Device turned off. (B) Device in operation.

The dosimetric parameters of the equipment are listed in table 2.

Table 2

Dosimetric parameters of the photobiomodulation (PBM) boot

The sessions will be held in the home by the participants themselves every day for the 60-day period. The participants will receive written instructions on the handling of the device, application time and frequency of use, as well as oral clarifications at the initial assessment and each return appointment. The manufacturer, Cosmedical, has not had and will not have any role in data collection and analysis, decision to publish or preparation of this manuscript. The PBM device is lined with a transparent plastic material that can be disinfected with 70% alcohol before and after use. To improve and monitor adherence to the study protocol, the participants will be contacted daily throughout the entire period.

OutcomesIncidence of ulcer (main outcome)

The incidence of ulcers on the feet will be assessed in all intervention sessions as well as 30 and 60 days after the beginning of the study through a clinical examination. The participants will be instructed to report any ulcer that appears at times other than those described.

Secondary outcomesAssessment of peripheral neuropathy

The evaluation of PN will be conducted after 60 days of intervention. This comprehensive assessment, as outlined in the initial assessment, will include several components: the Semmes-Weinstein monofilament test19 21 22 to measure tactile sensitivity, vibratory sensitivity tested with a 128 Hz tuning fork19 23 and the examination of the Achilles reflex.19 24 Furthermore, two standardised scales will be used to evaluate signs and symptoms: NSS and NDS.

Assessment of peripheral artery disease

The assessment of PAD, detailed in the initial evaluation, will be repeated 60 days following the intervention. This reassessment will encompass several key components: the evaluation of ischaemia degree, a Doppler ultrasound examination, an assessment of claudication and thermography of the feet.6 19 30 The degree of ischaemia will be quantified through the measurement of the ABI and TBI.19 31 32 The vascular ultrasound will focus on parameters such as peak systolic velocity, resistance index and waveforms of the distal segments of the anterior and posterior tibial arteries, as well as the fibular artery. Claudication will be evaluated using the Edinburgh Claudication Questionnaire,33–35 which has been validated for Brazilian Portuguese by Makdisse et al.36 For thermography, infrared imaging will be captured using a highly sensitive infrared sensor to assess foot temperature variations.

Assessment of quality of life

The evaluation of the quality of life, as delineated in the initial assessment, will be repeated 60 days following the intervention. This assessment will employ the Diabetes 21 Questionnaire, a shortened version of the Diabetes 39 Questionnaire,38 39 which has been validated for use by Sousa et al.40

The data will be stored anonymously in the Open Science Framework platform and will be available through a justified request. The findings of the study will be disseminated through publication in a peer-reviewed journal.

Research team

The team will be composed of the following:

One assessor (physician) will perform the initial assessment and reassessments (with exception of the Doppler ultrasound, ABI and TBI) with no knowledge of the allocation of the participants to the different groups. This researcher will obtain informed consent from potential trial participants.

One assessor (vascular surgeon) will perform the Doppler ultrasound and determine the ABI and TBI at the initial assessment and reassessments with no knowledge of the allocation of the participants to the different groups.

One researcher (nurse) will open the envelopes stipulating allocation, will deliver the appropriate PBM equipment (active or sham) and will instruct the participants on its use at home.

One researcher, who will not participate in any assessment, will perform the randomisation and prepare the envelopes to ensure allocation concealment.

Two medical residents will contact the participants on a daily basis for the control of the use of the LED devices, offering counselling and clarifying doubts, without participating in any of the assessments.

Data analysis plan

The normality of data distribution will be determined using the Shapiro-Wilk test. Based on the results, the most appropriate statistical test will be selected. Continuous data will be expressed as mean ± SD. Kaplan-Meier survival analysis will be used to estimate the incidence of ulcers on the feet throughout the study period. The t-test, χ2 test, Fisher’s exact test and Cox regression analysis will be used to determine factors associated with the development of diabetic ulcers on the feet. A risk assessment will be conducted using the data collected, employing statistical methods such as Cox regression analysis or survival analysis. Additionally, a subgroup analysis will be performed, considering participants at moderate and high risk for the development of foot ulcers as well as age. A criterion for adherence to the protocol will be established, classifying participants as ‘sufficient treatment’ if they complete at least 30 sessions (50% of the total). Only those meeting this adherence criterion will be included in the primary analysis. Both intention-to-treat and per-protocol analyses will be performed to validate our findings. A sensitivity analysis will be conducted for different adherence levels (70% and 90%) to assess the impact on study outcomes and explore dose-response relationships. Statistical analysis will be performed using IBM SPSS Statistics, V.25 (IBM Corporation, NY, USA). Variables with a p value <0.05 will be considered significantly associated with the outcome.

Trial status

The recruitment started in March 2024. We are planning to finish recruiting by June 2025 and complete the study by December 2025.

Discussion

PBM is the administration of a light source with the aim of enhancing tissue repair, modulating inflammation and the immune response and generating analgesia. For such, laser or LEDs are used, generally with low power (<500 mW), which do not cause heating of the tissue or considerable structural changes.41 42 Lasers and LEDs have been successfully used in PBM, but LEDs have the advantages of a lower cost, safe for home use, ease of application over larger areas and the possibility of using more than one wavelength simultaneously.43 44

The therapeutic effects of PBM depend on the absorption of the light by specific tissue chromophores, such as the enzyme cytochrome c oxidase, which is part of the respiratory chain of mitochondria and mainly absorbs light in the red (620–750 nm) and near infrared (750–950 nm) portions of the spectrum.42 44 45 The molecular mechanisms that explain the results of PBM have not been fully clarified, but the most widely accepted hypothesis is that light is absorbed by specific chromophores (depending on the wavelength), such as the mitochondrial enzyme cytochrome C oxidase, generating the synthesis of ATP, the release of Ca2+ through ionic channels, the activation of transcription factors, cell signalling, regulation of the progression of the cell cycle, activation of enzymes and a change in the genic expression of numerous cell products.41–44 46 The combined use of more than one wavelength can reach structures located at different depths, thus enhancing the effect of therapy.44 45 PBM has demonstrated good results in the treatment of DFU, in cases of neuropathy, and the prevention of inflammatory conditions of the mucosae and skin.14–18 42 47–49

The positive effects of PBM on DFU are associated with the modulation of inflammation and the enhancement of repair mechanisms, as previously mentioned. In addition, PBM improves tissue perfusion by stimulating blood flow in the microcirculation, increasing erythrocyte deformability and promoting angiogenesis, even in cases of ischaemia.50–52 Furthermore, the benefits of PBM extend to diabetic neuropathy. A systematic review concluded that PBM with laser effectively reduces neuropathic pain in diabetic patients, demonstrating safety and cost-effectiveness.53 A randomised controlled trial also found significant pain reduction and improved quality of life in patients receiving PBM on the plantar surface of the feet and lower back over 12 weeks, recommending it as a safe non-invasive adjunctive therapy for peripheral neuropathic pain.54 Furthermore, a study involving 50 patients treated with PBM for 10 days reported pain reduction, increased vibration perception threshold, decreased neuron-specific enolase levels, and enhanced foot sensitivity and quality of life after 30 days.55 The antihyperalgesic potential of PBM is linked to its capacity to reduce TNF-α and IL-1β levels, decrease p38-MAPK mRNA expression and diminish neuronal sensitisation through modulation of Ca2+ dynamics.56 Furthermore, preclinical findings suggest that PBM may increase nerve growth factor levels, improve myelin morphology and metabolism, reduce axoplasma-myelin separation, enhance C fibre density and elevate both the total number of mitochondria and their metabolic state.57

Multidisciplinary prevention methods for DFU include glycaemic control, self-care of the feet, the use of adequate footwear, treatment of local risk factors, physical exercises and therapeutic education for the patient and family.2 6–8 12 13 However, the incidence of diabetes has been increasing throughout the world, along with the complications of DFU.1–5 It is therefore essential to seek additional prevention strategies.

This project is proposed to assess the effect of PBM combined with self-care and routine outpatient follow-up on the prevention of DFUs in patients at moderate to high risk of developing this condition, thus establishing an innovative, non-invasive prevention therapy with no side effects.

Ethics statementsPatient consent for publication

Not applicable.