Cerebellar Involvement in Immune-Mediated Pediatric Acute Ataxia: Clinical Spectrum, MRI Findings, and Predictors of MOG Antibody Positivity.

Acute ataxia is a common pediatric neurological presentation with diverse etiologies. While autoimmune mechanisms are increasingly recognized, the spectrum of autoimmune cerebellar ataxia in children remains poorly characterized. This study aimed to systematically compare the clinical, neuroimaging, and laboratory features of children with immune-mediated ataxia against seronegative controls, with particular focus on cerebellar involvement and predictors of MOG antibody positivity. This retrospective case-control study enrolled 73 children with acute ataxia who tested positive for neural autoantibodies or CSF oligoclonal bands (OCBs), and 59 seronegative controls. The immune-mediated cohort included subgroups with MOG, NMDAR, GD1b, MBP antibodies, or isolated OCBs. Demographic, clinical, neuroimaging, and laboratory data were analyzed. Multivariate logistic regression identified independent predictors of MOG antibody positivity. Immune-mediated patients exhibited higher acute mRS scores (3.07 vs. 2.63, p = 0.003), more frequent lethargy / altered sensorium (30.1% vs. 10.2%, p = 0.005), and higher relapse rates (15% vs. 0%, p = 0.002) than seronegative controls. Cerebellar MRI abnormalities were observed in 42.8% of MOG-positive patients and 77.7% of OCB-positive patients. MOG-positive patients (n = 20) had more severe encephalopathy and multifocal MRI lesions involving cerebral hemispheres, brainstem, and cerebellum compared to OCB-positive (n = 38) and seronegative groups. Multivariate regression identified younger age (OR = 0.718), higher acute mRS score (OR = 5.917), and cranial MRI abnormalities (OR = 27.746) as independent predictors of MOG positivity (all p < 0.01). Pediatric autoimmune cerebellar ataxia encompasses a heterogeneous spectrum. MOG antibody-associated ataxia represents a severe encephalitic syndrome with widespread MRI lesions including frequent cerebellar involvement, while isolated OCB positivity defines a clinically mild but relapsing-prone subgroup with predominant cerebellar MRI findings. Early recognition of clinical and imaging "red flags" enables timely risk stratification and targeted immunomodulatory intervention in children with autoimmune cerebellar ataxia.