Blood and CSF levels of brain-derived neurotrophic factor in patients with encephalopathy/encephalitis: a systematic review and meta-analysis

Background Brain-derived neurotrophic factor (BDNF) is critical for enhancing the survival and growth of neurons and modulating the synaptic plasticity. BDNF levels have been demonstrated to be changed in plasma and cerebrospinal fluid (CSF) following brain insults such as inflammation or ischemia or infection in several studies. Currently, there is no systematic review regarding BDNF levels in encephalitis or encephalopathy patients. Considering inconsistency between studies, we aimed to pool the data from existing studies to determine whether blood or CSF levels of BDNF are different in patients with encephalopathy/encephalitis. Methods We comprehensively searched Web of Science, PubMed, Scopus, and Embase databases to identify eligible studies. The last search occurred in December 2022. Results 12 studies met our inclusion criteria and ten studies including 283 patients and 323 healthy controls were enrolled in this meta-analysis. In comparison to controls, patients with encephalitis/encephalopathy had higher levels of BDNF in their CSF [standardized mean difference (SMD) = 1.48, 95% CI 0.18–2.77; P = 0.03)], while their blood levels of BDNF did not differ significantly [standardized mean difference (SMD) = 0.27, 95% CI = − 0.71 to 1.25; P = 0.58)]. Moreover, regarding the heterogeneity among studies reporting BDNF blood levels, we performed two subgroup analyses based on the disease etiology and the specimen (plasma and serum); none of them indicated statistically significant difference in BDNF levels between the subgroups ( P = 0.41 and 0.20, respectively). Conclusion Meta-analysis provides evidence that patients with encephalopathy/encephalitis have higher CSF levels of BDNF compared to controls.