Neuro-Behçet's disease: an update of clinical diagnosis, biomarkers, and immunopathogenesis

Neuro-Behçet's disease (NBD) is a more severe but rare symptom of Behçet's disease, which is mainly divided into parenchymal NBD (p-NBD) involving brain stem, spinal cord, and cerebral cortex. Non-p-NBD manifests as intracranial aneurysm, cerebral venous thrombosis, peripheral nervous system injuries, and mixed parenchymal and non-parenchymal disease. p-NBD is pathologically characterized by perivasculitis presenting with cerebrospinal fluid (CSF) pleocytosis, elevated total protein, and central nervous system (CNS) infiltration of macrophages and neutrophils, which are subdivided into acute and chronic progressive stages according to relapsing-remitting courses and responses to steroids. The diagnosis of NBD depends heavily on clinical features and magnetic resonance imaging (MRI) findings. The lack of laboratory biomarkers has hindered standard diagnostics. CSF interleukin (IL)-6 is the most investigated dimension of NBD and correlates with NBD activity, therapeutic responses, and prognosis. Further investigations have focused on inflammatory biomarkers that reflect the activation of innate and adaptive immune responses. Higher levels of CSF migration inhibitory factor and immunosuppressive acidic protein indicated the activation of macrophages in the CNS; increased IL-17, IL-10, T-bet/GATA-3, and retinoic acid related orphan receptor (ROR)-γt/Foxp3 ratios, marking the disrupted scale of the Th1/Th2 and Th17/Treg axis; and elevated B-cell activating factor of the TNF family (BAFF) and IgA/IgM intrathecal synthesis, suggesting that B cells play a dominant role in NBD. CNS destruction and degeneration as a consequence of neuroinflammatory cascades were confirmed by elevated CSF levels of NFL, β2MG, and MBP. Autoantibodies, including anti-STIP-1, anti-Mtch1, anti-B-Crystallin, and anti-m-Hsp65, provide substantial evidence for autoimmune essence and underlying microbiological infections in NBD immunopathogenesis. We summarized opinions on the clinical diagnosis, biomarkers, and pathological findings of NBD.