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New Study on Incidence of Parkinsonism

A group of brain disorders caused by misfolded proteins are called proteinopathies and include Parkinson’s disease, Lewy body dementias, multiple system atrophy, progressive supranuclear palsy and corticobasal syndrome. A new study analyzed how frequently new cases of parkinsonism were diagnosed in one geographic area of the U.S. and which proteinopathies were the underlying cause.

Studying medical records, Rodolfo Savica, MD and researchers at Mayo Clinic identified all new diagnoses of parkinsonism in Olmstead County, MN for a period of 15 years, from January, 1991 through December, 2005. Researchers identified 542 parkinsonism diagnoses made during that time. Movement disorder experts reviewed the medical records in each case and made a diagnosis as to the most likely underlying case of the parkinsonism.

75.5% of cases were presumed to be caused by proteinopathies, the most common being Parkinson’s disease in 48% of cases. Combined diagnoses of dementia and parkinsonism were made in 20% of cases. The number of new cases identified per year of Lewy body disorders was 21.0 per 100,000 person-years overall and this rate increased steeply with age. (Lewy body disorders include Parkinson’s disease, Lewy body dementias and multiple system atrophy.) Men had a higher incidence than women for most types of parkinsonism. Findings at autopsy confirmed the clinical diagnoses in 81.5% of cases.

Parkinsonism associated with tau proteins was classified in 20 cases, resulting in an incidence of 1.0 new cases overall per 100,000 person years, with the most common cause being progressive supranuclear palsy (16 cases). Other causes were drug-induced parkinsonism (36 cases), vascular parkinsonism (11 cases), amyotrophic lateral sclerosis (1) and parkinsonism secondary to surgery (1). There were 84 cases that remained unspecified.

The authors indicated this as the first population-based study to examine the incidence of clinically-presumed proteinopathies. The study suggests that Lewy body disorders are the most common cause of parkinsonism, and that within that group of disorders, Parkinson’s is most common, followed by Lewy body dementias. More work is needed to understand how the rate of new diagnoses of Lewy body disorders relates to overall prevalence (or total patient population) of these diseases. An upcoming study from the same author will futher explore the specific incidence of dementia with Lewy bodies (DLB) and Parkinson’s disease dementia (PDD).

The study was published online in May 2013 in JAMA Neurology and was funded by the National Institute on Aging and the Mayo Foundation for Medical Education and Research.

Savica R, Grossardt BR, Bower JH, Ahlskog JE, Rocca WA. Incidence and Pathology of Synucleinopathies and Tauopathies Related to Parkinsonism. JAMA Neurol. 2013 May 20:1-7. Abstract