Case Report: A case of diffuse midline glioma, H3 K27-altered presenting with long-segment spinal cord lesions.

Diffuse midline glioma H3 K27-altered is a subtype of pediatric-type diffuse high-grade gliomas, characterized as an infiltrative high-grade glioma involving midline structures with H3 K27 mutation. This clinically rare entity poses diagnostic challenges in the early stages and carries an extremely poor prognosis. We report a case of diffuse midline glioma H3 K27-altered, primarily manifesting as spinal cord lesions, and detail its clinical characteristics to enhance understanding of this disease entity. A 21-year-old male presented with "progressive quadriparesis over 7 months." Seven months prior, he had developed bilateral lower limb weakness (grade II) following a cold. MRI at a local hospital revealed abnormal signals at T2-T5, diagnosed as "myelitis." The disease progressed with lesion expansion despite treatment with glucocorticoid pulse therapy and intravenous immunoglobulin. The patient visited our hospital 7 months after the onset of the disease. At that time, the patient exhibited grade I muscle strength in the right upper limb and grade 0 in all other limbs, with sensory impairment below the neck. MRI revealed abnormal signals in the medulla oblongata and thoracic spinal cord. The patient received high-dose glucocorticoid pulse therapy again, but the symptoms did not improve despite treatment. The definitive diagnosis of diffuse midline glioma H3 K27-altered was established through spinal cord biopsy. The patient was discharged from the hospital due to respiratory failure 12 days post-diagnosis.