Therapeutic effects of photobiomodulation in the speech-language-hearing clinic: an integrative literature review

ABSTRACT

Purpose:

to conduct a literature review on the therapeutic effects of photobiomodulation applicable to speech-language-hearing therapy.

Methods:

the databases searched were the Cochrane Library, Virtual Health Library, Medical Literature Analysis and Retrieval System Online (MEDLINE) via PubMed, and Web of Science/ISI.The selected articles were original ones whose abstracts were available and that evaluated the therapeutic effect of photobiomodulation in situations related to speech-language-hearing practice.

Results:

the sample comprised 23 articles, most of them being indexed in PubMed. The fields of health with the largest number of publications were Physical Therapy and Medicine. The sample size ranged from1 to 99 people, aged 15 to 77 years, and the most applied wavelength was the infrared one. Most of the studies had positive photobiomodulation application results - although in a few publications the effects of this treatment modality were assessed in a combination with rehabilitation exercises.

Conclusion:

photobiomodulation benefits different disorders treated by speech-language-hearing therapists, however, there is a broad methodological diversity, lacking specific protocols for the ideal dosimetry for each disorder.

Keywords:
Audiology; Speech, Language and Hearing Sciences; Stomatognathic System; Low-Level Light Therapy; Voice

RESUMO

Objetivo:

realizar revisão de literatura sobre efeitos terapêuticos da fotobiomodulação aplicáveis à Fonoaudiologia.

Métodos:

foram utilizadas as bases de dados Biblioteca Cochrane, Biblioteca Virtual de Saúde, Medical Literature Analysis and Retrieval Sistem online (Medline) via PuBmed e Web of Science/ISI. Foram selecionados artigos originais e com resumos disponíveis que avaliaram o efeito terapêutico da fotobiomodulação em situações relacionadas à prática fonoaudiológica.

Resultados:

a amostra consistiu em 23 artigos, a maioria indexada na PubMed. As áreas da Saúde com maior número de publicações foram Fisioterapia e Medicina. O tamanho das amostras variou de 1 a 99 indivíduos, faixas etárias entre 15 e 77 anos e o comprimento de onda mais aplicado foi o infravermelho. A maioria das pesquisas evidenciou resultados positivos da aplicação da fotobiomodulação, embora, em poucas publicações tenham sido avaliados os efeitos dessa modalidade de tratamento associados a exercícios de reabilitação.

Conclusão:

a fotobiomodulação traz benefícios em diferentes distúrbios tratados por fonoaudiólogos, no entanto, há grande diversidade metodológica e ausência de protocolos específicos da dosimetria ideal para cada distúrbio.

Descritores:
Audiologia; Fonoaudiologia; Sistema Estomatognático; Terapia com Luz de Baixa Intensidade; Voz

Introduction

Low-level laser (LLL) therapy to modulate cell and tissue physiology can be applied from light sources such as a light-emitting diode (LED) and low-level light amplification by stimulated emission of radiation (laser)¹.

Photobiomodulation (PBM) is the application of light to a biological system to induce a photochemical process - especially in the mitochondria, stimulating the production of energy as adenosine triphosphate (ATP)². Hence, cell metabolism is increased, producing effects such as analgesia³, tissue regeneration, wound scarring⁴, decreased muscle fatigue⁵, and so forth. Besides these, evidence from the application of neuromodulation to different regions of the nervous system points to an increase in brain perfusion, resulting in cognitive and behavioral improvement in neurological diseases such as dementia, traumatic conditions, and Parkinson’s disease, besides possible cognitive improvements in healthy people⁶.

Speech-language-hearing therapists are increasingly interested in joining the group of professionals who use PBM, as it is a noninvasive and nontoxic therapeutic resource with promising results. Some studies have recently evaluated its results in speech-language-hearing rehabilitation in the fields ofAudiology and Oral-Motor Function and observed, respectively, reduced tinnitus⁷and improved electrical activity in the orbicularis oris muscle⁸.

Despite the scarcity of studies in speech-language-hearing pathology, the application of PBM in disorders also treated by speech-language-hearing therapists has already been reported in the literature. In Audiology, there are studies on tinnitus^9,10 and hearing loss¹¹. In Language, there is research on the use of neuromodulation in healthy people¹² andischemic¹³, neurodegenerative^13,14, and traumatic diseases¹⁵ reporting improved naming capacity in aphasic patients, as well as improvements in other cognitive skills¹⁶. In Oral-Motor Function, which concentrates a large part of the research, temporomandibular disorder (TMD)^17-22, nipple fissures^23-25, and facial palsy (FP)^26-30 treatment is highlighted. Lastly, in the field of Voice, a study has been conducted on vocal fatigue³¹.

Even though PBM has been used in the speech-language-hearing clinic, there is no robust evidence of its effects as a therapeutic technique, considering clinical aspects such as 1) most effective application (before, during, after exercises); 2) wavelength to be used; 3) application time; and 4) dosimetric parameters. Therefore, speech-language-hearing interventions with PBM application need to be standardized, using structured clinical protocols for the rehabilitation of different clinical conditions.

Given the above, this study aimed to conduct a literature review on the PBM therapeutic effects applicable to speech-language-hearing therapy.

Methods

Research Strategies

This is an integrative literature review. The studies were selected based on the following steps: development of the research question, search in the literature, and critical analysis of the studies³².

The following research question guided the search on which the review was based: What are the therapeutic effects of PBM on disorders treated by speech-language-hearing therapists?

The articles were selected from the Cochrane Library, Virtual Health Library (VHL), Medical Literature Analysis and Retrieval System Online (MEDLINE) via PubMed, and Web of Science/ISI databases. The descriptors used were “Audiology”, “Speech, Language and Hearing Sciences”, “Stomatognathic System”, “Low-Level Light Therapy”, and “Voice”, and their combinationsin English, Portuguese, and Spanish. The other speech-language-hearing specializations, as they are not descriptors, were used in the search as free terms.

Selection Criteria

After finding the studies, they were screened by title and abstract. This stage was independently carried out by two speech-language-hearing evaluators. Considering the inclusion and exclusion criteria,23 articles were selected to be read in full.

Original articles whose full text was available, published between 2010 and 2020, assessing the therapeutic effects of PBM in situations applicable to speech-language-hearing therapy were selected.

Duplicated articles, found in more than one database, were excluded, as well as those evaluating only analgesia or other PBM effects, not considering functional aspects, studies in animals, and ongoing research, whose final results had not yet been published.

Hence, the sample comprised 23 articles, of which 19 were inMEDLINE/ PubMed and four, inVHL (Figure 1).

Figure 1:
Selection and analysis of the articles

The texts were fully read and analyzed considering year and place of publication, language, first author’s professional education, study design, classification of the level of scientific evidence by the Oxford scale³³, objectives, sample, types of PBM, wavelength, number of sessions, areas of application, energy per point, time of application, and outcomes in each identified theme. The Oxford scale³³ classifies, particularly, the study designs; the evidence is classified in levels, from best to worst, as 1a, 1b, 1c, 2a, 2b, 2c, 3a, 3b, 4, and 5.

Literature Review

Based on the methodology applied, 23 references were selected - 10 national and 13 international articles. Regarding language, 21 articles had been published in English (91.3%), one in Portuguese (4.35%), and one in Spanish (4.35%). Brazil led the number of articles, followed by the United States (Figure 2).

Figure 2:
Number of publications per country

As for the year, a larger number of publications were from 2012 and 2019 (Figure 3).

Figure 3:
Number of publications per year

Concerning the first author’s professional education, six (26.1%) were physical therapists, six (26.1%) were physicians, four (17.4%) were dentists, two (8.7%) were nurses, two (8.7%) were speech-language-hearing therapists, one (4.3%) was a psychologist, and two (8.7%) studies did not include this information.

Regarding the research design, there were 17 (73.9%) clinical trials (level of evidence: 2B) and six (26.1%) descriptive studies (level of evidence: 4). Of the selected clinical trials, 12 studies (70.5%) useda placebo, andseven (41.1%) described the blinding of the evaluators, thepatients, or both.

The sample size ranged from one to 99 people, aged 15 to 77 years. Only one article was conducted with children.

Concerning the type of PBM, 16 articles usedlaser (69.6%), six used LED (26.1%), and one (4.3%) did not describe it. The infrared wavelength was applied in 13 pieces of research (56.5%), the red one was applied in five (21.7%), and a combination of both was applied in four publications (17.4%).

The analysis of the publications led to the identification of the following main themes: Therapeutic PBM effects in Audiology, highlighting publications on hearing loss and tinnitus (n=3); in Oral-Motor Function, highlighting the treatment of TMD (n=6), nipple fissures (n=3), and facial palsy (n=5); and in Language (n=5) and Voice (n=1).

The results were described separately, by fields of specialization (Figures 4 to 9).

Figure 4:
Therapeutic effects of photobiomodulation related to the field of Audiology (treatment of hearing loss and tinnitus)

Figure 5:
Therapeutic effects of photobiomodulation related to the field of Language

Figure 6:
Therapeutic effects of photobiomodulation related to the field of Oral-Motor Functions (treatment of temporomandibular disorders)

Figure 7:
Therapeutic effects of photobiomodulation related to the field of Oral-Motor Functions (treatment of nipple fissures)

Figure 8:
Therapeutic effects of photobiomodulation related to the field of Oral-Motor Functions (treatment offacial palsy)

Figure 9:
Therapeutic effects of photobiomodulation related to the field of Voice

Therapeutic PBM Effects in Audiology

In the field of Audiology, PBM has been used in treatments for various decades, mainly to treat tinnitus^9,10.

In the two studies found, the number of treatment sessions ranged from three to 10^9-11, and two studies used the red wavelength^9,11. The areas of application were the external acoustic meatus and tympanic membrane, and the application time ranged from 4 to 20 minutes.

The LLL transmeatal stimulation in 43 patients was not an effective therapeutic means to treat tinnitus⁹. In another research, though, the tinnitus duration decreased significantly in the group treated with laser¹⁰.Studies are scarce in the national literature, as well as treatment protocols. The discrepancy in results may be due to the small sample and the different types of treatment protocols used. These factors hinder the adequate comparison between the results.

Although one piece of research did not reveal any improvement in hearing, speech comprehension, or cochlear function after applying LLL¹¹, there is evidence proving the increase in ATP production after PBM² - which could sustain the theory of beneficial effects in cases of hearing loss.

Therapeutic PBM Effects in Language

Five selected studies evaluated the effects of transcranial neurostimulation in both healthy participants¹² (with evidenced improvement in executive function) and cases of lesions in the nervous system from ischemic¹³, neurodegenerative¹⁴, and traumatic factors¹⁵. One study demonstrated improvementin the linguistic capacity of aphasic patients after neurostimulation¹⁶.

The dosimetry ranged from 10.65 to 196 Joules (J) per session; the treatment lasted 8 to 18 sessions; the stimulation time was 4 to 36 minutes; both laser and LED were used - most of the time, infrared wavelength.Transcranial laser stimulation is a new, safe, and noninvasive brain PBM method that has benefits such as increased blood flow, decreased edema, neuroprotection, neurogenesis, and an anti-inflammatory effect⁵.The frontal cortex was stimulated in most of the studies, while there was no association between language exercises and neurostimulation in any of them.

One study revealed an improvement in the neuropsychological scores in traumatic brain lesions after transcranial stimulation¹⁵. There is a growing need for rehabilitation strategies, as the different cognitive rehabilitation techniques and combinations can be useful to treat various cognitive deficits due to traumas in the nervous system³⁴.

Research with PBM in cases of ischemic, neurodegenerative, and traumatic diseases show cognitive improvement, probably due to factors such as increased brain blood flow and neurogenesis⁵.

The ideal energy wavelength, duration, dosage, flow, and density for each treatment have not yet been established, and it is not clear how long the neurostimulation effects last, although the evidence suggests that transcranial stimulation is an important medical tool to treat cognitive deterioration.

Therapeutic PBM Effects in Oral-Motor Function

TMD Treatment

The studies presented various objectives, such as assessment of bite strength¹⁷, masticatory performance and analgesia¹⁸, effects of different dosimetry on the treatment of TMD¹⁹ in oral-motor function²⁰, comparison of PBM effects, either alone or in combination with manual therapy²¹, and impact on the amplitude of mandibular movements²².

In only one study, electromyography was used to assess muscle electrical activity²². In four studies, the interventions were applied to experimental and placebo groups^17-19,23. In one, the PBM effects were combined with manual therapy, which did not reveal any increase in therapy effectiveness when the treatment modalities were combined²¹. These data agree with a study that demonstrated eased pain and improved masticatory function and orofacial myofunctional conditions with myofunctional therapy, both alone and in combination with laser therapy⁸. Another research, on the other hand, did not evidence any changes in mandibular movements or electrical activity of the masticatory muscles²² with laser application. The lack of a standardized protocol may contribute to discrepancies in the findings, as the dosimetry, time of exposure, wavelength, irradiation points, and the number of applications are important factors to determine the use of LLL therapy on damaged tissues.

In the last research carried out by speech-language-hearing pathologists²⁰, it was found that speech-language-hearing therapy conducted after analgesia with LLL balanced the oral-motor functions in TMD. However, that therapy began one month after finishing LLL therapy, which was not described.

The number of sessions ranged from six to 10, and the most used wavelength was the infrared. Five studies applied laser, and the main application points were the masticatory musculature, temporomandibular joint, and external acoustic meatus^17-21. The dosimetry ranged from 0.96 to 12.64 J, and the application time per point ranged from 10 to 60 seconds.

Thus, the evidence does not make it possible to establish an application dosage window, and the lack of consensus on the measures limits the conclusions about PBM.

Therapeutic PBM Effects in Oral-Motor Function

Nipple Fissure Treatment

In the present study, three selected pieces of research evaluated the PBM effects on the treatment of nipple fissures due to breastfeeding. The number of sessions ranged from 1 to 12, the applied energy ranged from 0.6 to 2 J per point, and the application time ranged from 5 to 79 seconds on the affected region of the breast.

The selected articles aimed to evaluate the scarring and the eased pain when breastfeeding^24-26; two of them evidenced positive effects when using either LED or laser in the red and infrared wavelengths^23,24. A study that did not identify any improvement conducted only one session, which may have influenced the results²⁵. Research shows positive PBM effects on scarring and on the reduction of the inflammatory process, even after a surgical procedure³. The scarring effect may be due to physiological processes that take place when ATP production increases² in the cells, which stimulates mitosis and metabolism, and consequently increases the endothelium cell proliferation, angiogenesis, and speeds tissue reparation.

The literature lacks randomized controlled clinical trials that objectively assess whether the area with nipple fissures has decreased, as well as the ideal dosimetry and time of treatment to achieve the desired results.

Therapeutic PBM Effects in Oral-Motor Function

Facial Palsy Treatment

Five selected publications approached the use of PBM on peripheral facial palsy, four of which were cases of Bell’s palsy (BP). In idiopathic facial palsy or BP, there may be functional sequelae such as oral incompetence, contractures, dysgeusia, synkinesis, and hemifacial spasms³⁵.

Regarding the study designs, there were two case reports^26,27 and three clinical trials^28-30. Only one study was conducted with children²⁸. The LLL has been proposed as a painless, noninvasive treatment modality, with no side effects, and with faster clinical improvement³⁰.

The infrared laser was the most used, whereas the irradiated points, the dosage, laser contact application time, and the number of sessions varied widely between the studies. The number of stimulated points ranged from eight to 80, the energy density ranged from 4 to 20 J/cm², the irradiation time ranged from 10 seconds to 2.7 minutes, and there was an average of 11 to 18 treatment sessions.

A study conducted with 48 patients with BP demonstrated that low- and high-level laser combined with orofacial exercises is more effective in treatment than exercises alone²⁹. This corroborates another research with 46 subjects which also presented better results when applying combined treatments³⁰. Intervention can be enhanced by applying LLL, as it speeds nerve regeneration acting as a cell stimulant and connective tissue modulator³⁶.

A systematic review with meta-analysis evaluated pre-exercise PBM effects on large muscle groups and evidenced that laser therapy is effective to improve the exercise capacity of skeletal muscles⁴.

Two studies did not present full motor recovery²⁶ or any difference between the experimental and placebo groups²⁸. The results may vary when different dosages or application techniques are used - as there is no consensus in the literature concerning dosage, application time, and the irradiation points in peripheral facial palsy procedures³⁷.

Even though the studies evaluated facial nerve recovery using orofacial exercises combined with laser therapy, the first author was not a speech-language-hearing therapist in any of them.

Therefore, laser can be used as a complementary therapy for facial palsy recovery. It should be highlighted, though, that the literature lacks great randomized controlled clinical trials that consider the patients’ characteristics - such as their skin color and condition, whether it is acute, subacute, or chronic-, besides the ideal stimulation window, in order to prove the effectiveness of this therapeutic resource.

Therapeutic PBM Effects in Voice

There is a scarcity of studies on the effectiveness of PBM to treat voice disorders. Only one study assessed the effectiveness of low-level light therapy with LED irradiation to treat vocal fatigue in 16 vocally healthy people³¹.The results showed that the red light proved to be more effective in the acoustic, aerodynamic, and auditory-perceptual measures, with better responses one hour after the procedure. Recent research has demonstrated beneficial PBM effects on muscle fatigue based on the metabolic and photochemical effects, which help increase cell energy⁵. Also, there is evidence of greater proliferation and migration of epithelial cells of the human vocal fold in culture, as well as increased expression of some genes involved in tissue scarring, after PBM application³⁸.

Further studies are necessary to establish the ideal light dosages, the best effectiveness of the wavelengths (whether alone or in combination), and the time when to apply the dosages (before, during, or after the vocal technique) to furnish resistance to fatigue, speed recovery, or improve muscle performance.

Conclusion

This integrative review identified pieces of research that approached therapeutic PBM effects in situations related to speech-language-hearing practice. There is a concentration of studies on Oral-Motor Function, particularly on TMD treatment. There are also studies in the fields of Audiology, Language, and Voice, although in almost all of them the first author’s professional training was in some other field of health, especially Physical Therapy, Medicine, and Dentistry.

The results suggest that PBM benefits different disorders treated by speech-language-hearing therapists. However, considering the diversity of methodologies, scarcity of studies conducted by professionals of the field, lack of specific and standardized protocols for the ideal dosimetry for each disorder, the data in the literature are controversial, with questionable evidence of the application of this resource.

Hence, it is suggested that randomized controlled clinical trials be conducted by speech-language-hearing therapists of different fields of practice, with a detailed description of the dosimetric parameters and speech-language-hearing techniques used in the procedures, to prove the results, better guide their use by professionals of the field, and establish evidence within the Speech-Language-Hearing Sciences.

Acknowledgments

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - Brasil (CAPES) - Finance Code 001.

Conselho Nacional de Desenvolvimento Científico e Tecnológico- Brasil (CNPq - no. 309108/2019-5).

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• This study was carried out in the Department of Speech-Language-Hearing Sciences at the Faculdade de Medicina da Universidade Federal de Minas Gerais - UFMG, Belo Horizonte, Minas Gerais, Brazil.
• Research support source: Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - Brasil (CAPES) - Finance Code 001. Conselho Nacional de Desenvolvimento Científico e Tecnológico- Brasil (CNPq - no. 309108/2019-5).

Publication Dates

• Publication in this collection
  05 Mar 2021
• Date of issue
  2021

History

• Received
  23 July 2020
• Accepted
  05 Jan 2021