MOG-IgG-associated encephalitis and bronchopneumonia in a child with negative infection screening: a case report and literature review

Myelin oligodendrocyte glycoprotein (MOG) antibody-associated disorder (MOGAD) is a central nervous system demyelinating disease in children, frequently induced by infection. We report the case of a 9-year-10-month-old boy with a 13-day fever and headache. He was admitted to our hospital for fever of unknown origin. He was diagnosed with bronchopneumonia via chest X-ray and encephalitis via cranial magnetic resonance imaging (MRI) and laboratory tests, which revealed increased white blood cells (WBC) (67 × 10 6 /L) and a high proportion of segmented granulocytes (31%) in cerebrospinal fluid (CSF). Further examination showed positive serum MOG-immunoglobulin G (IgG). After treatment with high-dose methylprednisolone (20 mg/kg/day, 3 days) and gamma globulin (400 mg/kg/day, 5 days), the patient's temperature returned to normal with decreased CSF WBC count (11 × 10 6 /L) and segmented granulocytes (5%). No abnormal bacterial growth was found in CSF. Oral methylprednisolone (32 mg/day), calcitriol soft capsules (1 capsule/day), and calcium carbonate D3 tablets (1 tablet/day) were prescribed after discharge, with a follow-up examination 1 week later. We present a rare case of a child with fever of unknown origin, diagnosed with MOG-IgG-associated encephalitis, bronchopneumonia, and MOG-IgG seropositivity despite negative infection screening. This report offers new insights into atypical MOGAD and a reference for MOGAD diagnosis and treatment in children. It highlights the importance of conducting MOG-IgG tests in children with encephalitis and bronchopneumonia despite negative infection screening.