Repetitive transcranial magnetic stimulation as adjunctive treatment in Parkinson's disease: are we missing opportunities? An umbrella and scoping review.

Despite the availability of effective treatments, many symptoms of Parkinson's disease remain insufficiently addressed. Repetitive transcranial magnetic stimulation (rTMS), a non-invasive neuromodulation technique, may help fill these therapeutic gaps, but its clinical role remains unclear. We conducted an umbrella review of systematic reviews and a scoping review of original studies on rTMS for Parkinson's disease, focusing on motor and non-motor symptoms. Review-level evidence and guideline statements support probable benefit of high-frequency rTMS targeting bilateral motor areas (particularly primary motor cortex) for improving motor symptoms. Low-frequency stimulation of premotor and cerebellar circuits has also shown signals for reducing levodopa-induced dyskinesias, although evidence is less definitive. For non-motor symptoms, high-frequency rTMS of the left dorsolateral prefrontal cortex (DLPFC) appears clearly beneficial for depression, with positive signals for cognitive symptoms, while right-DLPFC stimulation has shown preliminary signals on sleep disturbances. Across most domains, conclusions are limited by small sample sizes, short follow-up periods, heterogeneous stimulation protocols, inconsistent outcome measures and variable methodological quality of both trials and reviews. Evidence therefore remains insufficient to support broad clinical implementation across many symptom domains. Future research should adopt a circuit-based, symptom-specific approach, aligning stimulation targets with the neural substrates of each symptom. This requires clear inclusion criteria, well-characterized patient subgroups and standardized outcome measures across studies. The current literature suggests that rTMS may have therapeutic potential as part of multidisciplinary Parkinson's disease care, but adequately powered and rigorous trials are needed to determine its clinical utility and define where it may meaningfully address persistent therapeutic gaps.