Costello, H;
Gould, R;
Abrol, E;
Howard, R;
(2019)
A systematic review and meta-analysis of the association between peripheral inflammatory cytokines and generalised anxiety disorder.
BMJ Open
, 9
(7)
, Article e027925. 10.1136/bmjopen-2018-027925.
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Abstract
Objective: Inflammation has been implicated in the aetiology of mental illness. We conducted the first systematic review and meta-analysis of the association between peripheral markers of inflammation and generalised anxiety disorder (GAD). Design: Systematic review and meta-analysis of studies measuring peripheral cytokine levels in people with GAD compared to controls. Data sources: MEDLINE(1950–), EMBASE(1947-), PsycINFO(1872–) and Web of Science(1945–) databases up until January 2018. Eligibility criteria: Primary, quantitative research studies of people with a diagnosis of GAD assessed using a standardised clinical interview that measured peripheral inflammatory markers. Data extraction and synthesis: Two independent reviewers extracted data and assessed study quality. Meta-analysis using a random-effects model was conducted for individual cytokines where data from three or more studies were available. Results: 14/1718 identified studies met inclusion criteria, comprising 1188 patients with GAD and 10,623 controls. In total 16 cytokines were evaluated. Significantly raised levels of CRP, IFN-γ and TNF-α were reported in GAD patients compared to controls in two or more studies. Ten further pro-inflammatory cytokines were reported to be significantly raised in GAD in at least one study. However, 5/14 studies found no difference in levels of at least one cytokine. Only CRP studies reported sufficient data for meta-analysis. CRP was significantly higher in people with GAD compared to controls, with a small effect size (Cohen’s d = 0.38, 0.06-0.69), comparable to that reported in schizophrenia. However, heterogeneity was high (I 2= 75%), in keeping with meta-analyses of inflammation in other psychiatric conditions and reflecting differences in participant medication use, co-morbid depression and cytokine sampling methodology. Conclusion: There is preliminary evidence to suggest an inflammatory response in GAD, but it remains unclear whether inflammatory cytokines play a role in aetiology. GAD remains a poorly studied area of neuroinflammation compared to other mental disorders and further longitudinal studies are required.
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