French guidelines for the diagnosis and management of primary central nervous system vasculitis.

Primary central nervous system vasculitis (PCNSV) is a rare and heterogeneous disease whose diagnosis relies on a combination of clinical, radiological, and laboratory findings, and which requires a multidisciplinary hospital-based approach involving neurologists, neuroradiologists, and internists (or rheumatologists). This protocol is based on expert consensus and registry data, and aims to optimise and harmonise the diagnostic and therapeutic approach to PCNSV. Diagnosis is challenging due to non-specific clinical and radiological features. The diagnostic process includes (1) confirming vascular involvement (via MRI and angiography), and demonstrating the inflammatory process (via lumbar puncture, contrast-enhanced MRI and vascular wall sequences), (2) excluding more common differential diagnoses (especially intracranial atherosclerosis in patients with vascular stenosis), (3) and as often as possible discussing a brain or meningeal biopsy. Histological evidence obtained from a biopsy remains the gold standard for diagnosis, especially in case of small-vessel involvement. The therapeutic strategy is divided into induction (to achieve remission) and maintenance phases (to prevent relapse). Induction therapy consists of high-dose corticosteroids combined with an immunosuppressant, most often intravenous cyclophosphamide, to achieve remission. The initial corticosteroid dose is maintained for 2-3 weeks, then gradually tapered over 12-18 months. Once remission is achieved, maintenance therapy is introduced, typically using oral or subcutaneous immunosuppressants such as azathioprine, methotrexate, or mycophenolate mofetil, for 18-24 months. Preventive measures address treatment-related complications, including osteoporosis, infections, and metabolic disturbances. Relapses occur in a significant proportion of patients, necessitating prompt reassessment and possible escalation of immunosuppression. These guidelines emphasise the importance of individualised care, regular follow-up, and treatment adjustment based on disease activity and patient tolerance.