Neuropathic Pain Intervention With tDCS in Brazilian Military Personnel (NeuBRAIN Trial)

The primary outcome is a reduction in pain intensity by at least 30% (Dworkim et al., 2004; Farrar et al 2001). It will be assessed using the 100 mm Visual Analogue Scale (VAS), which consists of straight lines 100 mm long indicating "no pain" on one end and "worst possible pain or most intense pain possible" on the other (Huskisson, 1974). The VAS is scored by measuring the distance from the "no pain" end of the line. Pain intensity will be assessed daily during the 10day intervention.

Before and after the interventions, sleep secondary outcomes will be assessed using the Pittsburgh Sleep Quality Index (PSQI), which global score ranges from 0 to 21, with a higher score indicating poorer sleep quality. Each of the 7 component scores also range from 0 to 3, where a higher score on each component signifies more difficulty.

Before and after the interventions, the Epworth Sleepiness Scale (ESS) will be applied. The ESS has a minimum score of 0 and a maximum score of 24. Higher scores indicate greater daytime sleepiness, with scores above 10 suggesting excessive daytime sleepiness. A higher score is therefore indicative of a worse outcome, as it signifies a greater tendency to fall asleep in various situations.

Before and after the interventions, we will apply the Visual Analogue Scale for Fatigue Severity (VAS-F). The VAS-F uses a 100 mm line and scores are determined by measuring the distance from one end of the line to the point the individual marks, resulting in a score between 0 and 100. A higher score indicates greater fatigue severity.

Sleep evaluation with Type 2 polysomnography (PSG) will be recorded at baseline and will access time in bed (minutes), time to sleep onset (minutes), total sleep time (minutes), sleep latency (minutes), REM latency (minutes), wake after sleep onset (minutes).

The Arousal Index (AI) in polysomnography will be measured by counting the total number of arousals during sleep and dividing it by the total sleep time.

Sleep efficiency (SE) will be calculated as the total sleep time (TST) divided by the total time in bed, multiplied by 100. A higher SE percentage indicates that more time in bed is spent actually sleeping. Normal sleep efficiency is generally considered to be 85% or higher.

Sleep stages will be scored by analyzing 30-second epochs of polysomnographic recordings using electroencephalogram (EEG), electrooculogram (EOG), and electromyogram (EMG) signals.

The Periodic Limb Movement Index (PLMI) is calculated as the number of periodic limb movements during sleep (PLMS) per hour of sleep time. According to the American Academy of Sleep Medicine (AASM) scoring criteria, a limb movement (LM) is scored if there is an increase in anterior tibialis electromyogram (EMG) activity of more than 8 microvolts above resting EMG, lasting between 0.5 to 10 seconds. Periodic limb movements (PLMS) are defined as a series of at least four consecutive limb movements, each separated by an inter-movement interval of 5 to 90 seconds. The PLMI is computed by dividing the total number of PLMS by the total sleep time in hours, yielding PLMS per hour of sleep (PLMS/h). A PLMI greater than 15 per hour in adults is considered clinically significant for periodic limb movement disorder.

A possible confounder to be controlled for will be assessed by the Pittsburgh Sleep Quality Index Addendum for Posttraumatic Stress Disorder (PSQI-A) addresses patients exposed to trauma and was validated in U.S. male military veterans (Insana et al., 2013) and also in Portuguese by Gonçalves and Lima (2014). Seven items assess the frequency of hot flashes; general nervousness; memories or nightmares of the traumatic experience; severe anxiety or panic, not related to traumatic memories; nightmares, not related to traumatic memories; episodes of terror or screaming during sleep without full awakening; and episodes of staged dreams (Germain et al., 2005).

The PSQI-A (Pittsburgh Sleep Quality Index Addendum for Posttraumatic Stress Disorder) ranges from 0 to 21. Higher scores indicate a poorer outcome in PTSD symptom severity and a worse sleep quality. Scores of 5 or less generally indicate good sleep quality. Higher scores on the PSQI-A are also associated with more combat exposure.

Possible confounders to be controlled for will be assessed by the Depression-Anxiety-Stress Scales-21 (DASS-21) validated for Portuguese (Lovibond and Lovibond, 1995; Vignola and Tucci, 2014), that measures the levels of depression, anxiety and stress based on behaviors and feelings experienced in the last seven days. The DASS-21 has a score range from 0 to 63, in which the total score is calculated by summing the scores from all three subscales (depression, anxiety and stress). Higher scores indicate a more severe or frequent experience of depression, anxiety, and stress symptoms, i.e., a worse outcome.

The sociodemographic data collected will include date of birth (DD/MM/YYYY)

The sociodemographic data collected will include age (years)

The sociodemographic data collected will include educational level (length in years).

The sociodemographic data collected will include marital status (single, married, widow, other)

The sociodemographic data collected will include pre-existing diagnoses (name of the disease)

The sociodemographic data collected will include medication currently and previously used that may interfere with the results.

Weight (kilograms) will be measured in a scale in the baseline.

Height will be measured in centimeters with a height and weight scale, in which a sliding bar that is lowered to touch the top of the person's head, and the measurement is then read from the scale's markings. In addition, weight and height will be combined to report body mass index- BMI - in kg/m2.