Unstimulated whole salivary flow in Sjogren's Syndrome: systematic literature review and meta-analysis

Background: Sjogren's Syndrome compromises the exocrine function, producing xerostomia and xerophthalmia. It can appear as an isolated condition or associated with other autoimmune diseases (polyautoimmunity). The Unstimulated Salivary Flow rate (UWSF) is used to quantify saliva production. There is no objective evidence to differentiate the values in patients with Sjogren's versus healthy people or patients with non-Sjogren's sicca. The objective of the present review was to evaluate the UWSF in patients with Sjogren's syndrome in comparison to controls (healthy and non-Sjogren's sicca patients). Methods: A systematic literature review was carried out (PRISMA guidelines). Analytical observational studies of cases and controls, cross-sectional studies, cohort studies and randomized clinical trials (including healthy controls) were considered. The Medline/OVID, Lilacs, Embase, and Cochrane/OVID databases were consulted. MeSH, DeCS, keywords, and Boolean operators were used. The meta-analysis (RevMan 5.2) was done through the random-effects model [mean difference (MD)]. Level and quality of evidence were evaluated by the Oxford Center Levels of Evidence and Joanna Brigs list respectively. Results: Thirty-two articles were included (20 were case-control studies, 6 were cross-sectional, 2 prospective cohort, 2 retrospective cohort, and 2 studies were abstracts) and 28 were meta-analyzed. The unstimulated whole salivary flow rate in the Sjogren's group was lower than in controls (healthy and patients with non-Sjogren Sicca syndrome) (MD-0.18 ml/min; 95% CI, - 0.24 to - 0.13; chi(2)-P-value < 0.00001). Heterogeneity was 97% and there was publication bias (funnel plot). The level of evidence was mostly 3 or 4. The quality of evidence was met (97% of items valued). Conclusion: For the first time, the unstimulated whole salivary flow rate is found to be lower in patients with Sjogren's syndrome compared to controls (healthy and non-SS sicca) through a meta-analysis.