Abstract
Objective:
The present study aimed to evaluate the effectiveness of the application of photobiomodulation therapy (PBMT) in the prevention of recurrent herpes labialis (RHL) through a randomized controlled clinical trial.
Background data:
RHL is a lifelong infection that effects patients' quality of life. In the literature PBMT has shown positive results preventing RHL, decreasing recurrences and severity of lesions. Despite the good results reported, there are still few controlled clinical studies published on the subject.
Methods:
For this study, 158 volunteers were recruited and were randomly divided into three study groups: Laser 1–1 J/point (L1J): n = 61, Laser 2–2 J/point (L2J): n = 50, and placebo–0 J/point: n = 47. The treatment consisted of a protocol of 15 sessions throughout 6 months and 2 years of follow-up posttreatment.
Results:
The results showed that L1J presented the most satisfactory results concerning the reduction of the number of lesions per year and less severity of recurrences in the long-term evaluation when compared with L2J. Both Laser Groups (L1J and L2J) were statistically more efficient than placebo in all aspects analyzed. All patients who received laser treatment (L1J and L2J) and presented recurrences had significant improvement in frequency and/or severity of lesions. No patient had side effects from treatment.
Conclusions:
PBMT can be effective in the reduction of the frequency of recurrences of RHL and in the severity of postirradiation lesions that may appear.
Keywords: laser, herpes labialis, photobiomodulation, prevention
Introduction
The herpes simplex virus (HSV-1) is present in 70–90% of the population, but manifests itself in 20–40% as recurrent herpes labialis (RHL) and it is a lifelong infection1,2 The manifestations of RHL causes pain and discomfort, as well as social constraint.3,4 The current medications available demonstrates a limited effect; they do not alter the frequency of recurrences.5,6 Photobiomodulation therapy (PBMT) can be an excellent alternative that offers patients greater wellbeing and reducing recovery time. PBMT is a noninvasive method that contributes to pain relief and reduces inflammation, in parallel with tissue repair processes by inducing cell proliferation and increasing stem cell differentiation.7 The exact biochemical mechanism resulting from PBMT has not yet been well established.8 Evidence suggests that the primary effect of PMBT is the stimulation of mitochondrial cytochromes, increasing cell respiration and increasing adenosine triphosphate (ATP) levels production. The overall result is an increase in metabolic energy and improved cell viability.9–12
High-powered lasers can be used to promote drainage of vesicular contents and local decontamination. Due to patient reports of pain during applications and the high cost of the equipment, this treatment is not widespread.13 On the other hand, low-power laser has been used to accelerate the healing process and minimize the frequency of RHL. Also, patients do not report pain and it is a more affordable technique. Recently, studies have shown that photodynamic therapy (PDT) has shown satisfactory results inactivating HSV-1 in vitro14–17 and has been applied in vivo with satisfactory results and proving to be more efficient than antiviral drugs.18–22 PDT consists of the interaction between a photosensitive dye (applied on the drained vesicle) and the low-powered laser to cause apoptosis or damage the membrane of a biological system by photo-oxidation.14,16,17
The PBMT has shown positive results in preventing RHL, decreasing recurrences and severity of lesions.19 Despite the good results reported in the literature using lasers in the treatment and prevention of RHL, there are still few controlled clinical studies published on the subject.23 Therefore, the objective of this study was to test protocols with two distinct parameters in a randomized, blinded study with 2 years of follow-up.
Materials and Methods
After approval by the Research Ethics Committee of the School of Dentistry of the University of São Paulo (FOUSP), 158 volunteers were recruited to participate in the study and randomly divided into three study groups (two laser groups and one placebo). The device used was a diode low-power laser (Therapy EC, DMC Equipamentos, São Carlos, SP, Brazil); its round spot has an area of 0.09 cm2, fixed power of 100 mW, energy 1–9 J, and red (660 nm) and infrared (808 nm) laser wavelength. It belongs to the Special Laser Laboratory in Dentistry (LELO) of FOUSP, with no conflicts of interest. To check the power emission of the device, a power meter (LaserCheck, MMOptics Ldta, São Carlos, SP, Brazil) was used routinely.
The methodology in this clinical trial was based on the study of Eduardo et al.24 All volunteers included in the study were over 18 years of age and had RHL. They were excluded if: pregnant, nursing, had skin diseases, had a recent history of drug use, or patients who used antiviral agents not prescribed during the treatment.
The diagnosis of RHL was done through extensive medical history anamnesis and thorough clinical examination. The parameters performed in the different groups and phases are described in Table 1. The treatment started when patients currently did not have RHL lesions. The treatment consisted of two phases. Phase 1 consists of 10 sessions and Phase 2 consists of 5 sessions 6 months after the end of Phase 1. Sessions had an interval of at least 48 h between them.
Table 1.
Description of Treatments Performed in the Study
| Group | Treatment | Wavelength (nm) | Power (W) | Energy per point (J) | Time (sec) | Energy density (J/cm2) | Number of points performed | Distance between points (cm) | Area of irradiation | Cumulative dose given in 15 sessions (J/cm2) |
|---|---|---|---|---|---|---|---|---|---|---|
| L1J | Preventive | 808 | 0.1 | 1 | 10 | 11.11 | 40–50 | 1 | Lips and perioral | 166.65 |
| L2J | Preventive | 808 | 0.1 | 2 | 20 | 22.22 | 40–50 | 1 | Lips and perioral | 333.3 |
| Placebo | Preventive | 0 | 0 | 0 | 20 | 0 | 40–50 | 1 | Lips and perioral | 0 |
| L1J and L2J | PDT | 660 | 0.1 | 4 | 40 | 44.44 | 4–7 | 1 | On lesion and the surrounding (If RHL occurred) | 44.44 (one session) |
| Placebo | PDT | 0 | 0 | 0 | 40 | 0 | 4–7 | 1 | Lesions and the surrounding (If RHL occurred) | 0 |
L1J, Laser 1–1 J/point; L2J, Laser 2–2 J/point; PDT, photodynamic therapy; RHL, recurrent herpes labialis.
Patients were evaluated for frequency and intensity of RHL before the start of treatment, previously to Phase 2, 6 months after the end of Phase 2, and 1 year after Phase 2 through questionnaires.
If RHL appeared during the treatment, PDT was performed. The vesicles were gently drained with the aid of a needle and then Methylene Blue (0.01%) dye solution was placed for 5 min. Then, the lesion was irradiated. In the crust phase, PDT was also performed (Table 1).
Continuous data were tested for normality using the Shapiro–Wilk test. The nonparametric data are expressed as median and interquartile interval. Comparisons between multiple groups for nonparametric distribution were performed using the Kruskal–Wallis test. Multivariable analysis for continuous dependent variable was performed with multiple-factor analysis of variance. For this test, we selected as independent variables with greater potential interference nexus and/or association detection in a univariable test. Nominal and ordinal categorical data are expressed in number and percentage. Comparisons between groups for categorical variables were performed using Chi-square or Fisher's exact test for 2 × 2 contingency tables. Binary dependent variables were analyzed using multiple logistic regression. For this test, the independent variables were selected through association with p < 0.2 in the Chi-square test. In the posttest analyzes with multiple comparisons, a Bonferroni correction was used. For this study, an alpha risk of 0.05 was adopted.
Results
Patients were randomized to Laser 1–1 J/point (L1J; 61 subjects, 38.6%), Laser 2–2 J/point (L2J; 50 subjects, 31.8%), or placebo (47 subjects, 29.7%). The groups proved to be balanced for the main variables with potential for interference in the study, with no significant differences being observed for such variables. The variables considered were: age, ethnic group, gender, comorbidities, use of alcohol or smoking habit and use of medication (Table 2).
Table 2.
Basal Characterization of Population and Recurrent Herpes Labialis Episodes
| L1J |
L2J |
Placebo |
p | All |
|
|---|---|---|---|---|---|
| (% ou 25–75%) | (% ou 25–75%) | (% ou 25–75%) | (% ou 25–75%) | ||
| Age (years)a | 34.7 (30.0–42.1) | 31.9 (27.1–40.1) | 34.7 (30.3–40.3) | 0.399 | 33.3 (28.8–40.8) |
| Faixa etária (years)b | 0.105 | ||||
| Up to 30 | 15 (25.0) | 21 (42.9) | 10 (23.8) | 46 (30.5) | |
| 30–50 | 35 (58.3) | 23 (46.9) | 29 (69.0) | 87 (57.6) | |
| >50 | 10 (16.7) | 5 (10.2) | 3 (7.1) | 18 (11.9) | |
| Genderb | 0.761 | ||||
| Female | 45 (73.8) | 35 (70.0) | 36 (76.6) | 116 (73.4) | |
| Male | 16 (26.2) | 15 (30.0) | 11 (23.4) | 42 (26.6) | |
| Alcoholism and/or smokerb | 0.973 | ||||
| No | 26 (42.6) | 21 (42.0) | 19 (40.4) | 66 (41.8) | |
| Yes | 35 (57.4) | 29 (58.0) | 28 (59.6) | 92 (58.2) | |
| RHL episodes: impact on quality of life (0–10)a | 10.0 (9.0–10.0) | 10 (9.0–10.0) | 10.0 (10.0–10.0) | 0.568 | 10.0 (9.8–10) |
| RHL episodes: pain scale (0–10)a | 6.0 (1.0–8.0) | 7.0 (5.0–8.0) | 7.0 (5.0–8.0) | 0.226 | 4.0 (7.0–8.0) |
Comparisons performed by the Kruskal–Wallis test.
Comparisons performed by Pearson's Chi square.
The median age was 33.3 (28.7–40.7) and had a predominance of females, consisting of 116 women (73.4%) and 42 men (26.6%). The patients included in this study reported that recurrences have a negative impact on their quality of life, as indicated by the quantification of the factor “discomfort” (Fig. 1).
FIG. 1.
Distribution of the value attributed to the impact of discomfort in episodes of RHL on an increasing scale from 0 to 10 (n = 158), in percentage. RHL, recurrent herpes labialis.
The factor associated with the greatest discomfort and most frequently reported was pain (in 37% of the sample), followed by esthetic factors and social embarrassment (indicated by 35%) and other factors (in the remaining 28%). The vast majority of individuals (87%) reported the presence of pain during the RHL events. When asked to score the pain they felt during the episodes (on a scale of 0–10), 75% of patients assigned scores ranging from 5 to 10, while 25% assigned scores from 0 to 4 (Table 2).
Posttreatment evaluation
In the first posttreatment evaluation, the occurrence of RHL had a distribution that reached a marginal p value (p = 0.054) for difference between groups (Table 3). The placebo group showed a higher number of recurrences than the L1J and L2J groups (p = 0.013 and 0.016, respectively), with no statistical difference between the laser groups (Fig. 2A).
Table 3.
Evaluations Posttreatment
| L1J |
L2J |
Placebo |
p | All |
|
|---|---|---|---|---|---|
| (% ou 25–75%) | (% ou 25–75%) | (% ou 25–75%) | (% ou 25–75%) | ||
| First evaluation posttreatment | |||||
| RHL eventsa | 0.054 | ||||
| No | 19 (42.2) | 11 (32.4) | 4 (14.8) | 34 (32.1) | |
| Yes | 26 (57.8) | 23 (67.6) | 23 (85.2) | 72 (67.9) | |
| Number of eventsb | 1.0 (0.0–2.0) | 1.0 (0.0–2.0) | 3.0 (1.0–4.0) | 0.007 | 1.0 (0.0–3.0) |
| Intensity of eventsa | 0.011 | ||||
| Very light | 10 (38.5) | 7 (31.8) | 1 (4.5) | 18 (25.7) | |
| Light | 8 (30.8) | 11 (50.0) | 7 (31.8) | 26 (37.1) | |
| Mild | 7 (26.9) | 3 (13.6) | 8 (36.4) | 18 (25.7) | |
| Severe | 1 (3.8) | 1 (4.5) | 6 (27.3) | 8 (11.4) | |
| Faster healinga | 0.001 | ||||
| No | 6 (23.1) | 2 (9.1) | 13 (59.1)** | 21 (30.0) | |
| Yes | 20 (76.9) | 20 (90.9) | 9 (40.9)** | 49 (70.0) | |
| Smaller lesionsa | <0.001 | ||||
| No | 4 (15.4) | 2 (9.1) | 14 (63.6)*** | 20 (28.6) | |
| Yes | 22 (84.6) | 20 (90.9) | 8 (36.4)*** | 50 (71.4) | |
| Less eventsa | <0.001 | ||||
| No | 9 (34.6) | 2 (9.1)** | 15 (68.2)** | 26 (37.1) | |
| Yes | 17 (65.4) | 20 (90.9)** | 7 (31.8)** | 44 (62.9) | |
| Shorter vesicular phasea | 0.072 | ||||
| No | 18 (69.2) | 17 (77.3) | 21 (95.5) | 56 (80.0) | |
| Yes | 8 (30.8) | 5 (22.7) | 1 (4.5) | 14 (20.0) | |
| Absence of paina | 0.033 | ||||
| No | 17 (65.4) | 15 (68.2) | 21 (95.5) | 53 (75.7) | |
| Yes | 9 (34.6) | 7 (31.8) | 1 (4.5) | 17 (24.3) | |
| Less paina | 0.001 | ||||
| No | 12 (46.2)* | 13 (59.1) | 21 (95.5)** | 46 (65.7) | |
| Yes | 14 (53.8)* | 9 (40.9) | 1 (4.5)** | 24 (34.3) | |
| Pain scale (0–10)b | 3.0 (0.0–6.0) | 3.0 (0.8–8.0) | 5.0 (3.0–8.0) | 0.102 | 4.0 (10.0–6.3) |
| No changea | 0.004 | ||||
| No | 25 (96.2) | 22 (100.0) | 16 (72.7)** | 63 (90.0) | |
| Yes | 1 (3.8) | 0 (0.0) | 6 (27.3)** | 7 (10.0) | |
| Second evaluation posttreatment | |||||
| RHL eventsa | 0.230 | ||||
| No | 15 (37.5) | 11 (34.4) | 3 (15.8) | 29 (31.9) | |
| Yes | 25 (62.5) | 21 (65.6) | 16 (84.2) | 62 (68.1) | |
| Number of eventsb | 0.0 (1.0–2.0) | 0.0 (1.0–2.0) | 1.0 (2.0–4.0) | 0.071 | 1 (0–2) |
| Intensity of eventsa | 0.041 | ||||
| Very light | 4 (16.0) | 8 (38.1) | 1 (6.3) | 13 (21.0) | |
| Light | 10 (40.0) | 9 (42.9) | 7 (43.8) | 26 (41.9) | |
| Mild | 9 (36.0) | 3 (14.3) | 3 (18.8) | 15 (24.2) | |
| Severe | 2 (8.0) | 1 (4.8) | 5 (31.3) | 8 (12.9) | |
| Faster healinga | 0.123 | ||||
| No | 5 (20.0) | 6 (28.6) | 8 (50.0) | 19 (30.6) | |
| Yes | 20 (80.0) | 15 (71.4) | 8 (50.0) | 43 (69.4) | |
| Smaller lesionsa | <0.001 | ||||
| No | 4 (16.0) | 3 (14.3) | 11 (68.8)*** | 18 (29.0) | |
| Yes | 21 (84.0) | 18 (85.7) | 5 (31.3)*** | 44 (71.0) | |
| Less eventsa | <0.001 | ||||
| No | 8 (32.0) | 3 (14.3)* | 14 (87.5)*** | 25 (40.3) | |
| Yes | 17 (68.0) | 18 (85.7)* | 2 (12.5)*** | 37 (59.7) | |
| Shorter vesicular phasea | 0.098 | ||||
| No | 19 (76.0) | 16 (76.2) | 16 (100.0) | 51 (82.3) | |
| Yes | 6 (24.0) | 5 (23.8) | 0 (0.0) | 11 (17.7) | |
| Absence of paina | 0.594 | ||||
| No | 24 (96.0) | 19 (90.5) | 14 (87.5) | 57 (91.9) | |
| Yes | 1 (4.0) | 2 (9.5) | 2 (12.5) | 5 (8.1) | |
| Less paina | <0.001 | ||||
| No | 10 (40.0) | 2 (9.5)** | 12 (75.0)** | 24 (38.7) | |
| Yes | 15 (60.0) | 19 (90.5)** | 4 25.0)** | 38 (61.3) | |
| Pain scale (0–10)b | 4 (2.0–5.5) | 3 (2.0–5.5) | 5 (1.2–7.5) | 0.547 | 4.0 (2.0–6.0) |
| No changea | <0.001 | ||||
| No | 25 (100.0) | 21 (100.0) | 11 (68.8)*** | 57 (91.9) | |
| Yes | 0 (0.00) | 0 (0.0) | 5 (31.3)*** | 5 (8.1) | |
| Third evaluation posttreatment | |||||
| RHL eventsa | 0.132 | ||||
| No | 10 (29.4) | 12 (42.9) | 2 (13.3) | 24 (31.2) | |
| Yes | 24 (70.6) | 16 (57.1) | 13 (86.7) | 53 (68.8) | |
| Number of eventsb | 1.0 (0.0–1.0) | 1.0 (0.0–2.7) | 2.0 (1.0–5.0) | 0.047 | 1.0 (0.0–2.0) |
| Intensity of eventsa | 0.719 | ||||
| Very light | 6 (25.0) | 7 (43.8) | 3 (27.3) | 16 (31.4) | |
| Light | 7 (29.2) | 4 (25.0) | 2 (18.2) | 13 (25.5) | |
| Mild | 10 (41.7) | 4 (25.0) | 6 (54.5) | 20 (39.2) | |
| Severe | 1 (4.2) | 1 (6.3) | 0 (0.0) | 2 (3.9) | |
| Faster healinga | 0.094 | ||||
| No | 3 (12.5) | 5 (31.3) | 5 (45.5) | 13 (25.5) | |
| Yes | 21 (87.5) | 11 (68.8) | 6 (54.5) | 38 (74.5) | |
| Smaller lesionsa | 0.091 | ||||
| No | 2 (8.3) | 5 (31.3) | 4 (36.4) | 11 (21.6) | |
| Yes | 22 (91.7) | 11 (68.8) | 7 (63.6) | 40 (78.4) | |
| Less eventsa | 0.014 | ||||
| No | 1 (4.2) | 4 (25.0) | 5 (45.5) | 10 (19.6) | |
| Yes | 23 (95.8) | 12 (75.0) | 6 (54.5) | 41 (80.4) | |
| Shorter vesicular phasea | 0.467 | ||||
| No | 21 (87.5) | 14 (87.5) | 11 (100.0) | 46 (90.2) | |
| Yes | 3 (12.5) | 2 (12.5) | 0 (0.0) | 5 (9.8) | |
| Absence of paina | 0.906 | ||||
| No | 22 (91.7) | 14 (87.5) | 10 (90.9) | 46 (90.2) | |
| Yes | 2 (8.3) | 2 (12.5) | 1 (9.1) | 5 (9.8) | |
| Less paina | 0.623 | ||||
| No | 7 (29.2) | 5 (31.3) | 5 (45.5) | 17 (33.3) | |
| Yes | 17 (70.8) | 11 (68.8) | 6 (54.5) | 34 (66.7) | |
| Pain scale (0–10)b | 4.0 (1.2–6.7) | 2.5 (0.2–4.7) | 3.0 (1.0–5.0) | 0.324 | 3.0 (1.0–5.0) |
| No changea | 0.356 | ||||
| No | 23 (95.8) | 14 (93.3) | 9 (81.8) | 46 (92.0) | |
| Yes | 1 (4.2) | 1 (6.7) | 2 (18.2) | 4 (8.0) | |
Comparisons performed by Pearson's Chi square.
Comparisons performed by Kruskal–Wallis test.
p < 0.05, **p < 0.01, and ***p < 0.001 and in the distribution of adjusted and standardized residues, corrected by the Bonferroni method.
FIG. 2.
Number of RHL events in the period between evaluations after treatment. (A) First evaluation after treatment. (B) Second evaluation after treatment. (C) Third evaluation after treatment. Comparisons among L1J, L2J, and placebo groups were performed using the Kruskal–Wallis test and posttest with Bonferroni correction. L1J, Laser 1–1 J/point; L2J, Laser 2–2 J/point.
The severity of the events was statistically different between the groups (p = 0.011). The positive association of the placebo group with severe injuries reached marginal p (p = 0.057), as well as the negative association of the same group with asymptomatic status (p = 0.073).
The healing time experienced by the patients was also different between groups. In L1J and L2J, patients reported a shorter healing time than in placebo (p = 0.001). In this comparison, patients in the placebo group were associated with the absence of faster lesion healing (p = 0.002).
There was also a difference in the occurrence of smaller injuries (p < 0.001) with a strong association of the placebo group not showing such improvement in comparison to the laser groups (p < 0.001). There was also a difference in the absence of pain (p = 0.033). The pain scale, however, did not reach a significant difference between the groups.
While 27.3% of the placebo group did not report any change from baseline, this number was only 3.8% in the L1J and 0% in the L2J group (p < 0.004), with an association of the placebo group with the absence of changes in relation to baseline (p = 0.007).
In the second posttreatment evaluation, the p value of recurrence rate, despite the numerical difference, was not significant. During this period, there was a difference in the intensity of the injuries reported by the patients (p = 0.041), where laser groups showed much better results.
While most patients in L1J and L2J reported smaller injuries, only 31.3% in the placebo group reported such improvement (p < 0.001), in fact, the placebo group was significantly associated with the absence of smaller lesions in the evolution (p < 0.001). Patients also differed in the impression that they had fewer recurrence than usual (p < 0.001), since most laser-treated patients had such a sensation, only 31.3% of the individuals in the placebo group reported it and strongly associating the negative response (p < 0.001). The patients in the laser and placebo groups also differed in the improvement of the experienced pain (p < 0.001). While 0% of the patients in the placebo group had such a characteristic (p = 0.003), in L1J and L2J patients reported less pain. Again, the placebo group was strongly associated with the absence of changes from baseline (p < 0.001), whereas 100% of patients in the laser groups claimed to have noticed positive changes with the treatment. There were no differences between groups in the pain scale.
In the third posttreatment evaluation, it was not possible to observe differences between groups in the recurrence rate. The number of recurrences between groups, however, was different (p = 0.047; Fig. 2C).
In contrast to the previous phases, it was not possible to detect differences between the groups in the intensity of the events. The impression of faster remission time reached only marginal p values for the differences observed in the groups (p = 0.094), such as the report of minor injuries (p = 0.091). Again, a difference was observed when patients were asked if they had fewer events than usual in the period (p = 0.014). The pain scale again did not differ between groups.
It is possible to observe that, according to patients' perception, L2J lost its effectiveness over time, whereas L1J improved over time, and Placebo group reported little improvement (Fig. 3).
FIG. 3.
Patients' reports of smaller lesions, faster healing, and lower frequency of events.
Evaluation of the annual number of RHL events
The average follow-up time for patients in the study was 711.0 (591.2–894.2) days. This parameter was not significantly different between groups. The invariable analysis of the average number of annual recurrences detected a significant difference between the groups (p = 0.039), showing more satisfactory results in laser groups than in the placebo (Table 4). The posttest analysis, however, did not identify a significant corrected p value for pairwise comparisons. Multivariate analysis was established with the inclusion of variables that demonstrated a significant association with the number of annual recurrences of herpes labialis. The model pointed out the treatment group as an independent variable associated with the number of recurrences per year (p = 0.037; Table 5), with partial η2, an effect size estimate value of 0.099, being considered a moderate impact effect. The baseline frequency of RHL per year demonstrated a greater influence on the determination of annual recurrence events during the study period (partial η2 = 0.348, p = 0.004). The posttest analysis showed a significant difference between L1J and the placebo group (p = 0.026). There were no significant differences between L1J and L2J, nor between L2J and the placebo group (Fig. 4).
Table 4.
Average Number of Recurrent Herpes Labialis Events Per Year, Average Pain Scale, and Average Follow-Up Time
| L1J |
L2J |
Placebo |
p | Todos |
|
|---|---|---|---|---|---|
| (% ou 25–75%) | (% ou 25–75%) | (% ou 25–75%) | (% ou 25–75%) | ||
| Number of events per year | 1.0 (0.4–2.6) | 1.6 (1.1–2.7) | 2.7 (1.0–4.9) | 0.039 | 1.6 (0.5–3.1) |
| Pain scale | 3.7 (1.3–6.0) | 3.2 (1.5–5.5) | 4.7 (2.7–6.2) | 0.375 | 4.0 (1.5–5.7) |
| Follow-up time in days | 784.0 (637.5–906.5) | 723.0 (595.0–938.5) | 645.5 (457.0–820.0) | 0.093 | 711.0 (591.2–894.2) |
Comparisons made with the Kruskal–Wallis test.
Table 5.
Multivariate Analysis for Relapses Per Year and Treatment Groups
| η2 partial | p | |
|---|---|---|
| Treatment group | 0.191 | 0.037 |
| Age group | 0.065 | 0.353 |
| Age group of first recurrent cold sores infections | 0.214 | 0.103 |
| Baseline frequency of RHL infections per year | 0.348 | 0.004 |
Test performed with analysis of variance of multiple factors after logarithmic normalization of the dependent span.
FIG. 4.
Number of RHL events per year. (A) Comparisons among L1, L2, and placebo groups. (B) Comparison between treatment with lasers groups and placebo. Comparisons were performed by multiway analysis of variance after logarithmic normalization of the number of events per year and adjusted for potential confounding variables. Multiple comparisons were corrected by Bonferroni method.
The same modeling strategy was used to analyze both groups treated with laser. The laser treatments showed a significant association with the number of recurrences (p = 0.038) with η2 of 0.099 (Table 6; Fig. 4). Again, the variable with the greatest significant effect on the number of annual recurrences was the baseline frequency of RHL infections per year, with a partial η2 of 0.204 (p = 0.022).
Table 6.
Multivariate Analysis for Recurrent Herpes Labialis Events Per Year and Laser Treatment
| η2 partial | p | |
|---|---|---|
| Laser treatment | 0.099 | 0.038 |
| Age group | 0.045 | 0.377 |
| Age group of first RHL event | 0.128 | 0.209 |
| Baseline frequency of RHL events per year | 0.204 | 0.022 |
Test performed with analysis of variance of multiple factors after logarithmic normalization of the dependent variable. Posttest analysis: Laser 1 versus Placebo: p = 0.026. L1J versus L2J and Lase2 versus Placebo, p = not significant. Multiple comparisons were corrected with the Bonferroni method.
Discussion
This randomized, blinded clinical study aimed to evaluate the effectiveness of PBMT in the prevention of RHL, analyzing the number of recurrences per year and the severity of lesions. It should be noted that previous studies have assessed the potential effectiveness of PBMT in treating RHL.25,26 The first of such evaluations, published in 1995 with a limited number of 36 patients, showed that the RHL individuals submitted to laser therapy displayed a lower frequency of lesions than the ones treated with acyclovir.27 Soon after this report, Schindl and Neumann showed that PBMT extended the recurrence interval from 3 weeks, observed in the placebo group, to 37.5 weeks.23 Although such results were definitely meaningful, this study design did not allow analyses of long-term effects of PBMT treatment.
More than a decade later, Carvalho et al detected a nonsignificant trend of fewer recurrences in patients who received PBMT compared with ones treated topically with acyclovir; this study, however, was not placebo controlled.28 Despite its limitations and lack of conclusiveness, this report opened promising perspectives in the field. Along these lines, a next study by Muñoz Sanchez et al revealed a lower number of recurrences in laser-treated RHL patients versus affected individuals submitted to conventional therapy after 1 year of therapeutic intervention.29 This treatment also led to a decrease in the frequency of lesions. It must be noted one more time, however, that this study was designed to evaluate the potential efficacy of PBMT in treating such lesions, not in preventing them.
To address the potential preventive role of PBMT on RHL, and based on previous protocols using different dosages and modes of irradiation, a follow-up study by Eduardo et al sought to develop a preventive therapy protocol for RHL based on the treatment of three cases.24 This approach led to successful results in such cases. This scenario motivated us to investigate this potential preventive effect of PBMT in an appropriately randomized and controlled study. Therefore, based on this study and additional information on potential protocols employing distinct dosages and methods of irradiation,27 we designed our current study looking for standardization of a potential PBMT preventive protocol for RHL. Of note, no previous study comprised the essential features displayed by our work:25,30 controlled, randomized, blinded, with inclusion of a placebo group, and an adequate number of patients. It must be pointed out that in our study, the patients were followed for 6 months to 2 years after the end of the applied treatment and it included three times as many participants as Vélez-González et al's study.30 Finally, our study did prove the effectiveness of PBMT in preventing RHL lesions.
Our study revealed significant effectiveness of PBMT in the prevention of RHL in both laser groups compared with placebo in all parameters associated with frequency of recurrences and patient-reported severity of lesions (size of lesions, healing time, pain, frequency). Although both laser groups yielded satisfactory results, they displayed subtle differences. Surprisingly, the L1J of patients presented a better response than the LJ2 for the various analyzed parameters. Indeed, the average of recurrences per year was lower and disease severity decreased over time in LJ1, whereas, despite excellent immediate results, the laser intervention decreased its effectiveness over time in the LJ2 group. Notably, 44 patients from both groups had no recurrence by 6 months after the end of the treatment, although this number decreased in the fourth questionnaire assessment: 14% of these individuals had no lesions at any point of the survey whereas 18% of them did not have additional lesions. On the other hand, all patients of the placebo group presented lesions during the study follow-up.
The percentual decrease in patients who did not develop RHL between the last two assessments and the increase in the average number of lesions suggest that a higher number of PBMT sessions may be required to some patients. Further studies should test this hypothesis and, if positive, optimize the long-term effect of this protocol. Despite the beneficial effects of PBMT revealed by our group, our study had the limitation of not having been carried out in a double-blind fashion. We believe, therefore, that future double-blind studies should also be performed to improve research in this field.
Some of the patients who developed new lesions reported that they started inside the nose, a site not included in the irradiation protocol. In these cases, we decided to extend the irradiated area to this region. As expected, this maneuver was effective in preventing lesions also in this additional site. The observed lesion migration suggests that an extended-site protocol should be evaluated in a future study.
Our findings are especially important for oncologic patients who suffer greatly from RHL.31 PBMT is already a proven treatment of supportive care in cancer patients, and especially in the management of oral mucositis.32–35 Our protocol associated with these treatments can lead to minimizing the need of systemic medications given that these patients already use an extensive range of medications. The main difference between treatments for mucositis and RHL is the wavelength used. In mucositis, PBMT is done with a red wavelength, whereas our preventive treatment for RHL is done with an infrared.33,35,36
It is also important to consider that the effectiveness of PBMT on RHL may depend on several factors, including the laser parameters (wavelength, energy, time), the patients' clinical status and individual features (age, immunocompetence), and the optical properties of the target tissue (chromophore, structure, thickness).37 Since these various factors are expected to interfere with the therapeutic/preventive response, future studies should address their contribution to refine the proposed treatment on a patient-to-patient basis.
The cellular and molecular mechanisms involved in the PBMT's beneficial effects on RHL are still largely unclear. This intervention may act on local cells, promoting changes in their immune properties that enhance the response to herpes virus infection. Systemic effects, however, cannot be ruled out. Regardless the nature of such mechanisms, our data suggest that the proposed treatment may abolish or reduce the need of oral and topical antivirals. Given the absence of PBMT side effects, this is likely the main benefit of this preventive approach.26 It must be emphasized, however, that the benefits of such an intervention extend beyond its effects on discomfort and pain, also avoiding social embarrassment and, consequently, significantly improving life quality.
In conclusion, it is imperative to acknowledge the relevance of RHL's negative impact on patients' lives. In this context, establishing a safe intervention that prevents or mitigates frequency and severity of recurrences are expected to dramatically reduce the burden of RHL in society.
Conclusions
Considering the number of recurrences per year, the difference between laser groups was statistically relevant in comparison to the placebo group, showing a positive result for using PBMT for preventing RHL, reducing the frequency of recurrences and severity of postirradiation lesions. No patients had side effects from the treatment.
Authors' Contributions
P.A.Z.: Investigation, data curation, writing—original draft, and visualization. L.F.O.: Validation, and writing—review and editing. E.H.W.: Formal analysis. L.H.A., A.C.C.A., and K.M.R.: Conceptualization, methodology, and writing—review and editing. C.de.P.E.: Conceptualization, methodology, validation, writing—review and editing, supervision, and project administration.
Author Disclosure Statement
No competing financial interests exist.
Funding Information
The authors would like to express their gratitude for the financial support of this study that was provided by FAPESP (process 2016/06335-2, October 1, 2016 to September 30, 2017) and by CAPES (Financing Code: 001/2019).
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