Case report of intracranial tumor with serum MOG-IgG positivity.

Objective: To deepen understanding of the correlation between intracranial tumor and serum myelin oligodendrocyte glycoprotein immunoglobulin G (MOG-IgG) positivity, emphasizing the importance of avoiding misdiagnosis. Methods: We report a case involving a 24-year-old Chinese male whose clinical manifestations included slowed responsiveness, dysarthria, and right-sided limb weakness. Beyond serum MOG-IgG positivity, the nature of the central nervous system lesion was further evaluated based on therapeutic response and multimodal imaging. Results: The patient exhibited serum MOG-IgG positivity with an upward trend in titers. Immunotherapy failed to provide sustained and effective control of disease progression. Integrating the therapeutic response and characteristic imaging changes, a final diagnosis of malignant intracranial tumor was reached. Following diagnosis, he declined further oncologic therapy and died one month later due to a pulmonary infection. Conclusion: Serum MOG-IgG positivity and an initial response to immunotherapy may be misleading and contribute to diagnostic confusion with inflammatory demyelinating disorders. In atypical or treatment-refractory MOG antibody-associated disease, clinicians should remain vigilant for the possibility of a central nervous system space-occupying lesion.