Mimics of Pediatric Small Vessel Primary Angiitis of the Central Nervous System

Objective Small vessel primary angiitis of the central nervous system is a rare and often severe disease characterized by central nervous system‐restricted inflammatory vasculitis on histopathology. Diagnosis requires brain biopsy for confirmation and is suggested prior to starting immunotherapy when feasible. However, emerging evidence suggests that other neuroinflammatory conditions may have a clinical and radiographic phenotype that mimics small vessel primary angiitis, at times with overlapping pathologic features as well. Such diagnoses, including myelin oligodendrocyte glycoprotein antibody‐associated disease and central nervous system‐restricted hemophagocytic lymphohistiocytosis, can be non‐invasively diagnosed with serum antibody or genetic testing that would prompt different monitoring and treatment paradigms. To determine the ultimate diagnosis of patients who were suspected prior to biopsy to have small vessel primary angiitis, we reviewed the clinical, radiographic, and pathological features of a cohort of patients at a single center undergoing brain biopsy for non‐oncologic indications. Methods Clinical data were retrospectively extracted from the medical record. Pathology and neuroimaging review was conducted. Results We identified 21 patients over a 19‐year time‐period, of whom 14 (66.7%) were ultimately diagnosed with entities other than small vessel primary angiitis that would have obviated the need for brain biopsy. Diagnoses included anti‐myelin oligodendrocyte glycoprotein antibody associated disease (n = 9), central nervous system‐restricted hemophagocytic lymphohistiocytosis (n = 3), anti‐GABA A receptor encephalitis (n = 1), and Aicardi‐Goutières syndrome (n = 1). Interpretation This study highlights the importance of pursuing now readily available non‐invasive testing for mimicking diagnoses before performing a brain biopsy for suspected small vessel primary angiitis of the central nervous system. ANN NEUROL 2023;93:109–119