Changes in Olfactory Bulb Volume in Parkinson’s Disease: A Systematic Review and Meta-Analysis

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.

Improvement of Olfactory Function With High Frequency Non-invasive Auricular Electrostimulation in Healthy Humans

“…In the meta-analysis and review (Li et al, 2016 ), it was reported that PD patients presented a significantly larger OB volume on the right hemisphere, indicating the presence of lateralized differences between the two hemispheres. In support, several articles have indicated that the right hemisphere is more important for higher-order processing of smell sensation that the left hemisphere (Zatorre et al, 1992 ; Jones-Gotman and Zatorre, 1993 ; Hummel et al, 1995 ).…”

“…Impairments in PD are associated with the presence of lewy bodies, which represent distinctive inclusion bodies that underlie neuroanatomical dysfunctions in this condition. Lewy bodies are present from the earliest stage of PD, identified in the olfactory nucleus and the OB, but also in the dorsal nucleus of the vagus nerve (DMV) (Li et al, 2016 ). The spread of lewy bodies throughout the stages of PD, initially begins at the DMV, then spreads throughout the brainstem nuclei to the substantia nigra-pars compacta and finally the cortex (Braak et al, 2003 ; Doty, 2012 ; Li et al, 2016 ).…”

“…Lewy bodies are present from the earliest stage of PD, identified in the olfactory nucleus and the OB, but also in the dorsal nucleus of the vagus nerve (DMV) (Li et al, 2016 ). The spread of lewy bodies throughout the stages of PD, initially begins at the DMV, then spreads throughout the brainstem nuclei to the substantia nigra-pars compacta and finally the cortex (Braak et al, 2003 ; Doty, 2012 ; Li et al, 2016 ). This evidence points to an important connection between the vagus nerve and the olfactory processing areas of the cortex which is responsible for the early development of olfactory dysfunction in PD.…”

T cell dysfunction in chronic hepatitis B infection and liver cancer: evidence from transcriptome analysis

“…Vice versa, the coinhibitory factor PD-1 negatively regulates CD8 +cell function by facilitating oxidative metabolism 48. The connection between PD and cancer has been raised but poorly characterised 49. Taken together, our GO and KEGG analysis of differentially expressed genes distinguished CD8 +T cell exhaustion associated with HCC from CHB and provided pivotal clues for future investigation.…”

Microstructural network alterations of olfactory dysfunction in newly diagnosed Parkinson’s disease

“…Specifically, patients with hypos-PD showed reduced activation in the bilateral rectus, orbitofrontal cortex (OFC), amygdala and parahippocampus and reduced functional connectivities between the left rectus and prefrontal, temporal, occipital, and limbic areas, compared with healthy controls (HCs) 14 . Structural MRI studies using region-of-interest (ROI) methods have unraveled the neuroanatomical basis of the metabolic and functional changes and have found that olfactory-related atrophy occurred not only in the primary olfactory cortex (e.g., the piriform and amygdala), but also extended to the OFC, temporal, parietal-occipital, and cingulate cortex in PD 9 , 15 – 17 .…”