Neuroimaging Evidence of Acupuncture Effects in Parkinson’s Disease: A Systematic Review of fMRI-Based Clinical Studies

Background/Objectives: Parkinson’s disease is the second most prevalent neurodegenerative disorder, and many patients seek adjunctive non-pharmacological treatments such as acupuncture, whose neural mechanisms remain poorly characterized. Functional magnetic resonance imaging (fMRI) allows those mechanisms to be examined in vivo. We systematically synthesized the available fMRI evidence on the neural effects of acupuncture in Parkinson’s disease and appraised the methodological quality of that evidence. Methods: EMBASE, MEDLINE, PubMed, ScienceDirect, The Cochrane Library, CENTRAL and SciELO were searched, with no restriction on year of publication. Eligible studies were clinical fMRI studies of acupuncture in patients with Parkinson’s disease, of any interventional or controlled cross-sectional design, published in English or Portuguese. Screening and data extraction were performed independently by two reviewers using Rayyan. Risk of bias was assessed with RoB 2 for studies with a randomized element and with ROBINS-I for non-randomized studies. Results: Seven studies, reported in eight publications and published between 2009 and 2024, were included, comprising 151 patients with Parkinson’s disease (147 contributing analysable data) and 36 healthy controls, with sample sizes from 8 to 74 participants. One was a three-arm randomized controlled trial, one was a random-order crossover placebo study, one a non-randomized two-group study, two were single-arm interventional studies, and two were controlled cross-sectional comparisons. GB34 was used in five of the seven studies, and all used 3-Tesla echo-planar BOLD imaging. Acupuncture was consistently associated with modulation of the precentral gyrus, prefrontal cortex, thalamus, cerebellum, insula and putamen, accompanied in individual studies by improvements in pain, gait or motor scores. Risk of bias was high in both studies with a randomized element and serious or critical in the five non-randomized studies; no study was at low risk of bias. Conclusions: These findings are preliminary and hypothesis-generating. They are not sufficient to establish clinical efficacy, to separate specific neuromodulatory effects from non-specific ones, or to support a change in clinical practice. Adequately powered, sham-controlled randomized trials with harmonized imaging protocols are required.