Spinal Cord Diffuse Midline Glioma: A Lethal Masquerade

Spinal cord diffuse midline gliomas (DMGs) are rare World Health Organization (WHO) grade IV neoplasms with a poor prognosis. Due to the limited number of reported cases and the absence of standardized treatment protocols, most patients undergo biopsy or subtotal resection followed by radiotherapy. We report a rare case of spinal DMG, H3K27-altered, WHO grade IV, in an 18-year-old male that was initially misdiagnosed as inflammatory myelopathy due to a partial clinical response to steroids leading to diagnostic delay. This case underscores the diagnostic challenges posed by longitudinally extensive intramedullary lesions, where initial steroid responsiveness does not exclude neoplasm and may simply indicate reduction of perilesional edema. It highlights the importance of identifying imaging red flags, specifically heterogeneous expansile cord lesions, cystic changes, and lack of significant radiological improvement or progression on prolonged steroid therapy, which should raise suspicion for DMG.