Parkinson’s disease (PD) is a chronic, progressive motor-system disorder due to the loss of dopaminergic brain cells. PD’s symptoms include tremor, rigidity, bradykinesia (slow movement), and impaired postural stability. The disease was first described in 1817, and the National Institute of Neurological Disorders and Stroke estimates that at least 500,000 people in the US are affected by PD, and that the cost to society in terms of public health and other financial aspects is over $6 billion a year. In our Special Topics analysis of PD, we examine the highly cited research in this field over the past decade and over the past two years.

Heavy-hitting research topics in PD over the past decade include studies of the parkin gene and the role of alpha-synuclein in the disorder. Other topics garnering attention include familial trends of PD, mechanisms behind the formation of Lewy bodies, and various forms of treatment, such as GPi pallidotomy, electrical stimulation therapy, and glial-cell-line-derived neurotrophic factor (GDNF). The possibility of using human embryonic dopamine neuron transplants is explored, as is a Drosophila model of PD. One paper reports on a five-year study of dyskinesia (difficulties with voluntary movement) in PD patients treated with ropinirole or levodopa. Another study examines the possibility of environmental causes in PD. Several review articles are featured, including the 1999 Annual Review of Neuroscience paper by Warren Olanow and William Tatton, "Etiology and pathogenesis of Parkinson’s disease," which Dr. Olanow discusses with us in an interview.

The most prevalent subject in the past two years on our list is the exploration of mutations in the leucine-rich repeat kinase 2 (LRRK2) gene, with seven papers total. There are also two reports of clinical trials using rasgiline in PD treatment. Other highly cited papers published in the past two years include bilateral deep-brain stimulation, animal models, whole-genome studies, GDNF therapy, and the prevalence of pathological gambling in PD patients treated with dopamine agonists.

Methodology

To construct this database, papers were extracted based on title-supplied keywords for Parkinson's Disease. The keywords used were as follows: 

parkinson*

The baseline time span for this database is 1996-December 31, 2006 (sixth bimonthly). The resulting database contained 10,298 (10 years) and  2,179 (2 years) papers; 23,117 authors; 87 countries; 1,067 journals; and 5,388 institutions.

Rankings

Once the database was in place, it was used to generate the lists of top 20 papers (two- and ten-year periods), authors, journals, institutions, and nations, covering a time span of 1996-December 31, 2006 (sixth bimonthly, an eleven-year period).

The top 20 papers are ranked according to total cites. Rankings for author, journal, institution, and country are listed in three ways: according to total cites, total papers, and total cites/paper. The paper thresholds and corresponding percentages used to determine scientist, institution, country, and journal rankings according to total cites/paper, and total papers respectively are as follows:

Entity:	Scientists	Institutions	Countries	Journals
Thresholds:	32	96	10	88
Percentage:	%1	%1	%50	%20

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