Samuel J. Westwood, PhD; Joaquim Radua, PhD; Katya Rubia, PhD
Background: Repetitive transcranial magnetic stimulation (rTMS) or transcranial direct current stimulation (tDCS) could provide treatment alternatives to stimulant medication for attention-deficit/hyperactivity disorder (ADHD), given some evidence for improvements in cognition and clinical symptoms. However, despite a lack of solid evidence for their use, rTMS and tDCS are already offered clinically and commercially in ADHD. This systematic review and meta-analysis aimed to critically appraise rTMS and tDCS studies in ADHD to inform good research and clinical practice.
Methods: A systematic search (up to February 2019) identified 18 studies (rTMS 4, tDCS 14; 311 children and adults with ADHD) stimulating mainly the dorsolateral prefrontal cortex (dlPFC). We included 12 anodal tDCS studies (232 children and adults with ADHD) in 3 random-effects meta-analyses of cognitive measures of attention, inhibition and processing speed.
Results: The review of rTMS and tDCS showed positive effects in some functions but not others, and little evidence for clinical improvement. The meta-analyses of 1 to 5 sessions of anodal tDCS over mainly the left or bilateral dlPFC showed trend-level improvements in inhibition and processing speed, but not in attention.
Limitations: Heterogeneity in stimulation parameters, patient age and outcome measures limited the interpretation of findings.
Conclusion: The review and meta-analysis showed limited evidence that 1 to 5 sessions of rTMS and tDCS, mostly of the dlPFC, improved clinical or cognitive measures of ADHD. These findings did not support using rTMS or tDCS of the dlPFC as an alternative neurotherapy for ADHD as yet. Larger, multi-session stimulation studies identifying more optimal sites and stimulation parameters in combination with cognitive training could achieve larger effects.
Submitted Oct. 28, 2019; Revised Feb. 6, 2020; Accepted Feb. 29, 2020; Early-released Oct. 1, 2020
Acknowledgements: The authors thank Sophie Wallace Hanlon (S.W.H.) for assisting S.J.W. with the literature search and study identification. We also thank Zahra Soltaninejad43,64 for providing additional and original data from her study for the meta-analysis, and for translating her paper into English.
Affiliations: From the Department of Child & Adolescent Psychiatry, Institute of Psychiatry, Psychology & Neuroscience, King’s College London, London, United Kingdom (Westwood, Rubia); the Institut d’Investigacions Biomèdiques August Pi i Sunyer, Barcelona, Spain (Radua); the Mental Health Research Networking Centre (CIBERSAM), Madrid, Spain (Radua); the Department of Clinical Neuroscience, Centre for Psychiatric Research and Education, Karolinska Institutet, Tomtebodavägen 18A, Stockholm, Sweden (Radua); and the Department of Psychosis Studies, Institute of Psychiatry, Psychology and Neuroscience, King’s College London, De Crespigny Park, London, United Kingdom (Radua).
Competing interests: K. Rubia has received a grant from Shire pharmaceuticals (now Takeda) for another project not relevant to this work on the effects of guanfacine and lisdexamfetamine on fMRI brain function in ADHD. No other competing interests were declared.
Funding: S. Westwood is supported by Action Medical Research (GN2426), the Garfield Weston Foundation and the National Institute for Health Research (NIHR) Biomedical Research Centre at South London and the Maudsley NHS Foundation Trust and King’s College London. K. Rubia receives research support from the Medical Research Council (MR/P012647/1) and the National Institute for Health Research (NIHR) Biomedical Research Centre at South London and the Maudsley NHS Foundation Trust and King’s College London. The views expressed are those of the author(s) and not necessarily those of the NHS, the NIHR or the Department of Health and Social Care. J. Radua is supported by Miguel Servet Research Contract MS14/00041 and CPII19/00009, and Research Projects PI14/00292 and PI19/00394 from the Plan Nacional de I+D+i 2013–2016 and and 2017–2020, the Instituto de Salud Carlos III-Subdirección General de Evaluación y Fomento de la Investigación and the European Regional Development Fund (FEDER).
Contributors: S. Westwood, J. Radua and K. Rubia designed the study. S. Westwood and K. Rubia acquired the data, which all authors analyzed. S. Westwood and K. Rubia wrote the article, which all authors reviewed. All authors approved the final version to be published and can certify that no other individuals not listed as authors have made substantial contributions to the paper.
Content licence: This is an Open Access article distributed in accordance with the terms of the Creative Commons Attribution (CC BY-NC-ND 4.0) licence, which permits use, distribution and reproduction in any medium, provided that the original publication is properly cited, the use is non-commercial (i.e. research or educational use), and no modifications or adaptations are made. See: https://creativecommons.org/licenses/by-nc-nd/4.0/
Meeting presentations: An oral presentation of this systematic review and meta-analysis was given by S. Westwood at the European Network for Hyperkinetic Disorders (Eunethydis) International Conference, Edinburgh on Sept. 23, 2018, and at the 3rd International Brain Stimulation Conference, Vancouver, Canada, and the World Federation of ADHD (WFA) 2019. In 2019, the meta-analysis results were presented by K. Rubia at the WFA in Lisbon, at the Eunethydis conference in Nijmegen and with S. Westwood at the National Institute for Health Research Maudsley Biomedical Research Council Conference in London.
Correspondence to: S.J. Westwood, Department of Child and Adolescent Psychiatry PO46, Social, Genetic and Developmental Psychiatry (SGDP) Centre, Institute of Psychiatry, Psychology and Neuroscience, King’s College London, 16 De Crespigny Park, London, SE5 8AF, United Kingdom; email@example.com