A Systematic Review on Disease-Modifying Therapies in Parkinsonian Disorders

Parkinsonian disorders, including Parkinson's disease, Lewy body dementia, multiple system atrophy, and progressive supranuclear palsy, are progressive neurodegenerative conditions with no treatment options to slow disease progression. This systematic review provides an overview of evidence of disease-modifying therapies that have been evaluated in clinical studies across these disorders, based on a comprehensive literature search up to May 2025. Eligible studies included clinical trials investigating pharmacological interventions aimed at slowing disease progression. Most clinical development has focused on Parkinson's disease, with limited progress in other Parkinsonian disorders. Therapies targeting alpha-synuclein, such as monoclonal antibodies and small molecules, have shown target engagement but limited clinical efficacy. Glucocerebrosidase-enhancing agents, particularly ambroxol, demonstrated promising biomarker and clinical signals in early-phase trials. Glucagon-like peptide-1 receptor agonists and kinase inhibitors have yielded mixed results, with some agents progressing to phase 3 trials. Neurotrophic factors, cell survival and neuroprotective therapies, stem cell therapies, and anti-inflammatory agents remain largely investigational, with limited evidence of efficacy. Repurposed drugs, including memantine and riluzole, have shown preliminary signals of benefit, though confirmatory trials are lacking. Despite substantial research efforts, no disease-modifying therapy has been approved for any Parkinsonian disorder. The heterogeneity of disease mechanisms and the limitations of current clinical endpoints, such as the Unified Parkinson's Disease Rating Scale, underscore the need for biomarker-driven approaches and stratified trial designs. Future success will likely depend on improved patient selection, mechanistic targeting, and the integration of fluid and imaging biomarkers to demonstrate disease modification.