Dysgeusia in parkinson's disease: a systematic review

Abstract

Background: Taste has an extreme importance on individual nutrition, health and quality-of-life status. Parkinson's disease (PD), one of the most frequent neurodegenerative disorders, is becoming a systemic disease with an increasing awareness to the importance of non-motor symptoms for early PD diagnosis and early intervention. Dysgeusia may be a non-motor symptom of PD, similar to olfaction, however its role in PD diagnosis have not been well established yet. Purpose: To determine whether taste function is impaired in patients with PD. Research strategy: A systematic review research was carried out on the 30 of November 2015, using PubMed, Cochrane Library, SciELO, Web of Science, Index of Portuguese Medical Journal (IndexRMP.pt) and National Guideline Clearinghouse (guideline.gov). The metaRegister of Controlled Clinical Trials and ClinicalTrials.gov were also searched. We utilized the following equation: (“taste” (MeSH) OR “taste*”) OR “dysgeusia” (MeSH) OR “taste disorders” (MeSH) AND (“Parkinson’s disease” (MeSH) OR “Parkinson*”). Selection criteria: We have selected original studies conducted with PD patients that investigated the symptoms, incidence, prevalence and severity of taste impairment. There was no restriction on the study design, and publication date or status, but on the PubMed database, we have activated filters concerning to species (humans), and language (English, French, German, Spanish, and Portuguese). Data Extraction: Independent extraction of articles by 2 authors in accordance with the pre-established selection criteria. A standardized template was filled including the following information: author, year, sample, diagnosis and severity of PD, cognition and therapeutic status, purpose, type of intervention, main results and study limits. Results: We have found 334 studies by using the keywords and above search criteria. After adjusting for duplicates 173 remained. Out of this total, 125 were excluded by the title, 26 by the abstract, and 11 after we read the full text. Thus, a total of 11 studies were selected and analyzed in this review. Conclusion: We have observed a lack of standardization on the measurement methods used to assess taste function in PD patients, with great heterogeneity in the participants samples, which reduces the effectiveness and reliability of the results. Even though, an impairment of taste in PD has been described by the majority of the studies, but the clinical usefulness of taste testing seems to be limited at present, and, therefore, further research is encouraged.