Abstract
ObjectiveThe changes in olfactory bulb (OB) volume in Parkinson’s disease (PD) patients have not yet been comprehensively evaluated. The purpose of this meta-analysis was to explore whether the OB volume was significantly different between PD patients and healthy controls.MethodsPubMed and Embase were searched up to March 6, 2015 with no language restrictions. Two independent reviewers screened eligible studies and extracted data on study characteristics and OB volume. Additionally, a systematic review and meta-analysis using a random-effects model were conducted. Publication bias was determined by using funnel plots and Begg’s and Egger’s tests. Subgroup analyses were performed to assess possible sources of heterogeneity.ResultsSix original case-control studies of 216 PD patients and 175 healthy controls were analyzed. The pooled weighted mean difference (WMD) in the OB volume between the PD patients and the healthy participants was -8.071 for the right OB and -10.124 for the left OB; these values indicated a significant difference among PD patients compared with healthy controls. In addition, a significant difference in the lateralized OB volume was observed in PD patients, with a pooled WMD of 1.618; these results indicated a larger right OB volume than left OB volume in PD patients. In contrast, no difference in the lateralized OB volume was found in healthy controls. No statistical evidence of publication bias among studies was found based on Egger’s or Begg’s tests. Sensitivity analyses revealed that the results were consistent and robust.ConclusionsOverall, both the left and the right OB volume were significantly smaller in PD patients than in healthy controls. However, significant heterogeneity and an insufficient number of studies underscore the need for further observational research.
Highlights
Parkinson’s disease (PD) is the most common progressive neurological disorder that severely threatens human health and quality of life
The pooled weighted mean difference (WMD) in the olfactory bulb (OB) volume between the PD patients and the healthy participants was -8.071 for the right OB and -10.124 for the left OB; these values indicated a significant difference among PD patients compared with healthy controls
A significant difference in the lateralized OB volume was observed in PD patients, with a pooled WMD of 1.618; these results indicated a larger right OB volume than left OB volume in PD patients
Summary
Parkinson’s disease (PD) is the most common progressive neurological disorder that severely threatens human health and quality of life. A recent autopsy study by Hawkes revealed significant neuronal loss in the anterior olfactory nucleus in PD patients, and this finding suggested a strong association between changes in the olfactory bulb (OB) and PD-associated olfactory dysfunction [7]. These olfactory deficiencies have been associated to functional and/or structural changes at the level of the OB [8,9,10], which is an important component of the olfactory system. A series of studies on the changes in OB volume observed between PD patients and healthy controls have reported variable findings. To resolve this controversial issue, a systematic review and meta-analysis was performed to comprehensively assess whether the OB volume was significantly different between PD patients and healthy controls
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