# Effects of Transcranial Direct Current Stimulation on Speech and Voice Changes in Parkinson's Disease: a Systematic Review with Meta-Analysis

## TL;DR

This study reviews evidence on how transcranial direct current stimulation (tDCS) affects speech and voice in Parkinson's disease patients.

## Contribution

It provides a systematic review and meta-analysis of tDCS effects on speech and voice in Parkinson's disease.

## Key findings

- Overall tDCS effect size was Z=0.89 (P=0.37), suggesting limited impact.
- Prefrontal cortex-targeted tDCS showed a larger effect size of 1.38 (P=0.17).
- Only three studies had low risk of bias, highlighting the need for more rigorous research.

## Abstract

This meta-analysis aims to evaluate the existing evidence on the effects of tDCS on speech and voice alterations in patients with PD.

PubMed, LILACS, EMBASE, Cochrane Central Register of Controlled Trials, Science Direct, Web of Science, Scopus, and gray literature searches: Google Scholar and Open Grey. The search included the descriptors: "Parkinson Disease, Transcranial Direct Current Stimulation, Voice, Speech" combined with AND and OR.

Patients with Parkinson's Disease, both sexes. Use of Transcranial Direct Current Stimulation (tDCS) to treat voice and speech parameters in patients with Parkinson's Disease.

A total of 1,345 articles were included, 14 articles in the systematic review and 6 articles in the meta-analysis. The risk of bias and level of evidence were assessed using REVIEW MANAGER 5.4.1 and GRADE software.

The results showed an overall effect size of tDCS of Z=0.89 (P=0.37). Studies targeting the prefrontal cortex (PFC) showed a larger effect size of 1.38 (P=0.17), thus demonstrating a greater impact on speech and voice outcomes with the use of tDCS for PD. Three studies presented a low risk of bias, and three studies presented an unclear risk.

Despite the small number of studies, the findings of this meta-analysis suggest the potential applicability of tDCS as an adjunctive tool in the treatment of voice and speech disorders in patients with PD.

Esta metanálise tem o objetivo de avaliar a evidência existente dos efeitos da tDCS nas alterações de fala e de voz de pacientes com DP.

PubMed, LILACS, EMBASE, Cochrane Central Register of Controlled Trials, Science Direct, Web of Science, Scopus e de literatura cinzenta Google Scholar e Open Grey. A busca incluiu os descritores: “Parkinson Disease, Transcranial Direct Current Stimulation, Voice, Speech” combinados com AND e OR.

Pacientes com a Doença de Parkinson, ambos os sexos. Uso da Estimulação Transcraniana por Corrente Contínua (tDCS) para tratar os parâmetros de voz e fala nos pacientes acometidos pela Doença de Parkinson.

Um total de 1.345 artigos, 14 artigos incluídos na revisão sistemática e 6 artigos na metanálise. O risco de viés e o nível de evidência foram avaliados pelo software REVIEW MANAGER 5.4.1. e GRADE.

Os resultados mostraram um tamanho de efeito geral da tDCS de Z= 0.89 (P=0.37). Estudos com área alvo no córtex pré-frontal (PFC) apresentaram maior tamanho de efeito 1.38(P=0.17), portanto com maior impacto para desfecho de fala e voz com uso de tDCS para DP. Três estudos apresentaram baixo risco de viés e três estudos apresentaram risco pouco claro.

Apesar do baixo número de estudos, os achados desta metanálise sugerem a potencial aplicabilidade da tDCS como ferramenta adjuvante no tratamento das alterações de voz e fala em pacientes com DP.