The burden of Parkinson's disease: a worldwide perspective

Over history, diseases have appeared and disappeared, or have increased or decreased in frequency. These epidemiological trends have occurred more dramatically for infectious diseases (eg, the eradication of small pox), but have also occurred for chronic diseases (eg, reduction of vitamin deficiencies and cardiovascular disease).1Jones DS Greene JA The decline and rise of coronary heart disease: understanding public health catastrophism.Am J Public Health. 2013; 103: 1207-1218Crossref PubMed Scopus (29) Google Scholar Over the past three or four decades, changing trends in the epidemiology of neurological diseases have been reported. In some high-income countries (primarily in North America and western Europe), the risk of stroke and dementia has declined, but the risk of Parkinson's disease and parkinsonism, amyotrophic lateral sclerosis, and late-onset multiple sclerosis has increased.2Rocca WA Time, sex, gender, history, and dementia.Alzheimer Dis Assoc Disord. 2017; 31: 76-79Crossref PubMed Scopus (17) Google Scholar, 3Rocca WA The future burden of Parkinson's disease.Mov Disord. 2018; 33: 8-9Crossref PubMed Scopus (7) Google Scholar Other regions of the world with different physical or social environments to North America and western Europe have shown different trends. An understanding of these epidemiological trends is essential to guide decision making in medicine and public health.2Rocca WA Time, sex, gender, history, and dementia.Alzheimer Dis Assoc Disord. 2017; 31: 76-79Crossref PubMed Scopus (17) Google Scholar, 3Rocca WA The future burden of Parkinson's disease.Mov Disord. 2018; 33: 8-9Crossref PubMed Scopus (7) Google Scholar E Ray Dorsey, Alexis Elbaz, and colleagues from the GBD 2016 Parkinson's Disease Collaborators4GBD 2016 Parkinson's Disease CollaboratorsGlobal, regional, and national burden of Parkinson's disease, 1990–2016: a systematic analysis for the Global Burden of Disease Study 2016.Lancet Neurol. 2018; (published online Oct 1.)http://dx.doi.org/10.1016/S1474-4422(18)30295-3Google Scholar now report in The Lancet Neurology an extensive summary of indirectly estimated changes in global prevalence, disability, and death rates related to Parkinson's disease between 1990 and 2016.4GBD 2016 Parkinson's Disease CollaboratorsGlobal, regional, and national burden of Parkinson's disease, 1990–2016: a systematic analysis for the Global Burden of Disease Study 2016.Lancet Neurol. 2018; (published online Oct 1.)http://dx.doi.org/10.1016/S1474-4422(18)30295-3Google Scholar The authors did a series of analyses, projections, and extrapolations using the data and methods of the Global Burden of Diseases, Injuries, and Risk Factors (GBD) Study.5GBD 2015 Neurological Disorders Collaborator GroupGlobal, regional, and national burden of neurolo gical disorders during 1990–2015: a systematic analysis for the Global Bu rden of Disease Study 2015.Lancet Neurol. 2017; 16: 877-897Summary Full Text Full Text PDF PubMed Scopus (806) Google Scholar Despite the limited number of high-quality data sources for large geographical regions, and the broad and complex assumptions made in the GBD analyses, the results are of public-health interest. For countries in which incidence or prevalence of Parkinson's disease have not been reported, this study provides some tentative figures that could be used for health planning and future projections. The authors concluded that worldwide the burden of Parkinson's disease has more than doubled over 26 years, from 2·5 million patients (95% uncertainty interval 2·0–3·0) in 1990 to 6·1 million patients (5·0–7·3) in 2016. They suggest that this increase is due partly to the ageing of the population (resulting from increasing life expectancy), and also to longer disease duration and possible changes in environmental or social risk factors. For studies based on registries or medical records, there might also have been increased recognition and coding of Parkinson's disease in routine medical care. Because prevalence reflects both the incidence and the duration of the disease, a central question is whether the risk or incidence of Parkinson's disease has increased in the past three decades. Some data point to an increase in incidence in some high-income countries.3Rocca WA The future burden of Parkinson's disease.Mov Disord. 2018; 33: 8-9Crossref PubMed Scopus (7) Google Scholar, 6Savica R Grossardt BR Bower JH Ahlskog JE Rocca WA Time trends in the incidence of Parkinson disease.JAMA Neurol. 2016; 73: 981-989Crossref PubMed Scopus (104) Google Scholar, 7Isotalo J Vahlberg T Kaasinen V Unchanged long-term rural-to-urban incidence ratio of Parkinson's disease.Mov Disord. 2017; 32: 474-475Crossref PubMed Scopus (8) Google Scholar However, some studies did not confirm the increase, or reported a decrease.8Darweesh SK Koudstaal PJ Ikram MA Trends in the incidence of Parkinson disease.JAMA Neurol. 2016; 73: 1497Crossref PubMed Scopus (2) Google Scholar It is possible that different countries have experienced different trends because of differences in the physical or social environment.3Rocca WA The future burden of Parkinson's disease.Mov Disord. 2018; 33: 8-9Crossref PubMed Scopus (7) Google Scholar For example, smoking, the use of agricultural pesticides, the availability of purified water, or head trauma, which have all been implicated as either potential protective or risk factors for Parkinson's disease, might have decreased in some countries but increased or remained stable in other countries.3Rocca WA The future burden of Parkinson's disease.Mov Disord. 2018; 33: 8-9Crossref PubMed Scopus (7) Google Scholar Therefore, we urgently need high-quality sources of data on incidence, prevalence, and risk or protective factors for Parkinson's disease in different countries or regions. The analyses by Dorsey, Elbaz, and colleagues confirm the higher prevalence of Parkinson's disease in men than women starting at age 50 years. This dimorphic pattern could provide a key to understanding the environmental or social risk factors for Parkinson's disease. The frequency of exposure to some risk factors (eg, smoking, head trauma, and use of pesticides) is different in men and women, and it is possible that the effects of these risk factors are different in men and women because of interactions with sex variables (eg, specific genes on chromosomes X or Y, effects of sex hormones, and effects of pregnancy) or gender variables (eg, different education or occupations).9Savica R Grossardt BR Bower JH Ahlskog JE Rocca WA Risk factors for Parkinson's disease may differ in men and women: an exploratory study.Horm Behav. 2013; 63: 308-314Crossref PubMed Scopus (42) Google Scholar, 10Kaasinen V Vahlberg T Suominen S Increasing age-adjusted male-to-female incidence ratio of Parkinson's disease.Mov Disord. 2015; 30: 286-288Crossref PubMed Scopus (5) Google Scholar Parkinson's disease is also aetiologically heterogeneous (different patients might have different causes) and multifactorial (multiple risk or protective factors might contribute to the disease in a given patient), in addition to being dimorphic (the multifactorial causes might involve factors affected by sex and gender). If the reported doubling of the number of patients with Parkinson's disease between 1990 and 2016 is real, and is confirmed by other studies, we can expect that the trend will continue in the next approximately 30 years. A relatively conservative projected doubling of the number of patients over the next 30 years would yield more than 12 million patients worldwide by about 2050.4GBD 2016 Parkinson's Disease CollaboratorsGlobal, regional, and national burden of Parkinson's disease, 1990–2016: a systematic analysis for the Global Burden of Disease Study 2016.Lancet Neurol. 2018; (published online Oct 1.)http://dx.doi.org/10.1016/S1474-4422(18)30295-3Google Scholar However, if population ageing continues, medical management keeps improving survival, and environmental or social risk factors remain stable or increase, we can expect an even greater increase in the number of patients. I agree with Dorsey, Elbaz, and colleagues that there is an urgent need for research focusing on identifying new preventive interventions and new treatments for people with Parkinson's disease. The preventive interventions might need to be tailored to men and women separately, and to specific countries or regions of the world. I report grants from the US National Institutes of Health. Global, regional, and national burden of Parkinson's disease, 1990–2016: a systematic analysis for the Global Burden of Disease Study 2016Over the past generation, the global burden of Parkinson's disease has more than doubled as a result of increasing numbers of older people, with potential contributions from longer disease duration and environmental factors. Demographic and potentially other factors are poised to increase the future burden of Parkinson's disease substantially. Full-Text PDF Open Access