Search Strategy

In this study, we conducted a systematic review of the literature using the Preferred Reporting Items for Systematic reviews and Meta-Analyses model (14). Relevant articles were identified from MEDLINE, Scopus, and Web of Science published until June 2017. No registered clinical trials were identified from http://clinicaltrials.gov or http://clinicaltrialsregister.eu. Our search was aimed to identify studies that reported the clinical response to different kinds of therapeutic interventions in adult subjects with VP diagnosis. As historically VP has been poorly defined, we included only those studies that clearly and systematically defined VP. Given the difficulties of establishing VP diagnosis, all results and conclusions must take into account these operational definitions (Tables 1 and 2). To avoid possible bias, studies that used levodopa response as part of the definition of VP were not included. We used the following terms and Mesh terms (medical subject headings): PD, secondary; parkinsonian disorders; vascular; blood vessels; therapeutics; vitamin D; ergocalciferols; levodopa; amantadine; aripiprazole; transcranial magnetic stimulation. Full details on the search algorithm can be found in the Supplemental data. Further analysis of the references of each article was carried out to find articles that could have been excluded by the search algorithm. Only articles published in English were considered. Also, using the information retrieved by the search criteria of this systematic review, we conducted a meta-analysis focused on the prevalence of response VP subjects have to levodopa therapy. We followed the MOOSE guidelines for conducting meta-analyses of observational studies (15). Results of the search strategy are summarized in Figure ​Figure11.

Flowchart for study selection.