What next in Parkinson's disease?

More than 200 years since the publication of James Parkinson's An Essay on the Shaking Palsy (1817), many uncertainties regarding the progressive neurological disorder now known by his name remain. This issue of The Lancet carries our first-ever Series dedicated to Parkinson's disease, which includes an exploration of some of the outstanding questions around the epidemiology, causes, and current treatment options for this disabling and currently incurable condition. Parkinson's is second only to Alzheimer's disease in the list of most common neurodegenerative disorders and, with increasing life expectancies and fewer competing causes of death, its prevalence is expected to increase to 12–17 million people by 2040. Such a rise will require increasing amounts of human and care resources, which will add to the strain already felt by health systems globally. The issue will be particularly acute in low-income and middle-income countries, where availability of treatments and supporting therapy are lowest; even in high-income countries, both minority ethnic groups and those in rural areas face broader challenges in accessing care. Difficulties in the diagnosis of Parkinson's (especially early disease) also hamper effective care, and there is much need for a better understanding of the specific needs of minority ethnic patients, in whom the clinical manifestations and morbidities associated with Parkinson's disease are still poorly described. As detailed in papers 1 and 2 of the Series, the pathogenesis of the disease remains largely elusive. The cause of Parkinson's disease is multifactorial and, although there is consensus among experts that Parkinson's is an age-related disease, questions regarding the extent to which Parkinson's can be attributed to external drivers (such as pollutants) do not yet have clear answers. Paper 3 reviews the latest evidence on the optimal management of Parkinson's disease. Ultimately, research needs to aim for treatments that can alter the course of the disease but, despite growing research funding, major breakthroughs have been few and far between. A move towards biologically based criteria for the classification of Parkinson's is proving controversial, but the hope is that these new criteria can help detect the disease in its early stages, preferably in the prodromal phase, which might also pave the way for further research on disease-modifying therapies. Meanwhile, clinical studies of new drugs to better treat dyskinesia and other motor symptoms are under way, as are trials covering several known mechanisms of disease in Parkinson's. Non-pharmacological approaches such as robotics to help with gait impairments and music-based interventions to help manage various non-motor symptoms also show promise. Additionally, the potential value of lifestyle interventions to improve control of Parkinson's symptoms should not be overlooked, particularly regarding physical activity and nutrition, which offer some means to take care out of the clinic and into a patient's home. Most health systems worldwide are ill-prepared to deal with the growing population of patients with Parkinson's disease. Despite an acute need for better access to specialist care, there is still much to be done in ensuring that essential drugs reach patients. 2017 data show that levodopa and carbidopa—mainstays of Parkinson's treatment—were consistently available in primary care settings in only 37 of 110 countries (and just three in Africa, and none in southeast Asia). Informal carers, especially women, remain essential for many patients with Parkinson's disease, yet their experiences are often overlooked, and there is little support for caregivers globally. Tackling stigma against the disease (which can lead to higher rates of depression, comorbidities, and mortality in individuals with Parkinson's) and dispelling the misconception that Parkinson's disease is a natural consequence of ageing can be achieved through education and advocacy—not least among health-care providers, especially to help to improve communication around a diagnosis of Parkinson's. A disease-modifying treatment to slow, halt, and reverse progression of Parkinson's disease must be the goal to strive for. But in the meantime, improvements in basic and specialist care for patients with Parkinson's disease—supporting caregivers, ensuring access to simple medication regimens, and expanding the provision of primary and multidisciplinary care for comorbidities—would make tremendous differences to the care and quality of life for millions of patients worldwide.