Neutrophil-to-lymphocyte ratio predicts diagnosis and prognosis of idiopathic sudden sensorineural hearing loss A systematic review and meta-analysis

Background: Chronic inflammation has been regarded as one of the causes of idiopathic sudden sensorineural hearing loss (ISSHL). Several individual studies have reported the association between neutrophil-to-lymphocyte ratio (NLR) and ISSHL. However, the findings have been inconsistent, and these data have not been systematically evaluated. Thus, we conducted this meta-analysis to further explore the predictive value of NLR on formation and prognosis of ISSHL. Methods: A comprehensive literature search was performed to identify eligible studies based on PubMed, Embase, Web of Science, and China National Knowledge Infrastructure. The Standardized mean deviation (SMD) with its 95% confidence interval (CI) was applied to be the effect size estimate. Results: A total 10 papers with 15 retrospective case-control studies, which included 1029 ISSHL patients (the case group) and 1020 healthy people (the control group), were selected for the meta-analysis of the relationship between NLR and onset of ISSHL. The NLR levels in the case group were observed to be higher than the control group (SMD= 1.65, 95% CI=1.20-2.09, P <. 001). The pooled results did not significantly change by the subgroup analyses based on study region, baseline matching, and laterality. Moreover, 9 publications with 12 retrospective cohort studies, which included 590 recovered ISSHL patients and 438 unrecovered ISSHL patients, explored the association between NLR and ISSHL prognosis, and the combined data showed that the NLR value was much higher in unrecovered patients rather than recovered patients (SMD= 1.27, 95% CI: 0.62-1.92, P <. 001). The subgroup analyses based on study region, laterality, type of steroid, medication administration, maintenance treatment, follow-up period, and definition of "recovered" further supported these results. Conclusion: The results of this meta-analysis suggest that NLR might be a useful biomarker to determine the onset and prognosis of ISSHL.