Systematic Review and Meta-Analysis of Sniffin Sticks Test performance
in different countries.
Abstract
Introduction: Olfaction impairment occurs in about 90% of patients with
Parkinson’s Disease. The Sniffin Sticks Test is a widely used instrument
to measure olfactory performance and is divided into three subtests that
assess olfactory threshold, discrimination and identification. However,
cultural and socioeconomic differences can influence test performance.
Objectives: We performed a systematic review and meta-analysis of the
existent data about Sniffin Sticks Test performance of Parkinson’s
Disease patients and healthy controls in different countries and
investigated if there are other cofactors which could influence the
olfactory test results. A subgroup analysis by country was performed as
well as a meta-regression using age, gender and air pollution as
covariates. Results: Four hundred and thirty studies were found and
sixty-six articles were included in the meta-analysis. Parkinson’s
Disease patients showed significantly lower scores on the Sniffin Sticks
Test and all its subtests than healthy controls. Overall, the
heterogeneity among studies was moderate to high as well as the
intra-country heterogeneity. The subgroup analysis, stratifying by
country, maintained a high residual heterogeneity. Conclusion: The
meta-regression showed a significant correlation with age and air
pollution in a few subtests. A high heterogeneity was found among
studies which was not significantly decreased after subgroup analysis by
country. This fact signalizes that maybe cultural influence has a small
impact on the Sniffin Sticks Test results. Age and air pollution have
influence in a few olfactory subtests.