A Case of Treatment-Refractory Tumefactive Multiple Sclerosis Mimicking Brain Abscess

A 47-year-old female presented with one week of left facial numbness following recent dental extractions. Initial brain magnetic resonance imaging (MRI) with and without contrast revealed a contrast-enhancing lesion in the right parieto-occipital lobe with mild diffusion restriction and surrounding vasogenic edema, as well as smaller enhancing lesions in the right frontal and parietal lobes. Empiric intravenous (IV) antibiotic treatment was started due to a high concern for odontogenic brain abscesses. Despite antibiotic treatment, repeat brain MRI revealed new contrast-enhancing lesions in the left pons and cerebellar peduncle, suggesting that infection was unlikely and antibiotics were discontinued. The differential diagnosis broadened to neoplastic, inflammatory, and demyelinating pathologies. A brain biopsy of the right occipital lobe lesion was pursued for a definitive diagnosis. Following the brain biopsy, the patient received five days of IV methylprednisolone 1 g daily, followed by a two-week oral prednisone taper with clinical improvement. Brain biopsy subsequently demonstrated macrophages, reactive lymphocytosis, and astrogliosis with loss of myelin, confirming the diagnosis of tumefactive multiple sclerosis (TMS). Over the subsequent two years, she experienced recurrent flares of TMS with new demyelinating lesions despite disease-modifying therapy (DMT) with ocrelizumab, resulting in progressive disability accrual. Upon transition to natalizumab, disease remission was achieved. This case highlights the diagnostic challenges of TMS as it may radiographically resemble odontogenic brain abscesses, particularly in the setting of recent dental infections. Brain biopsy may be required when neuroimaging and cerebrospinal fluid findings are inconclusive. This case also suggests that natalizumab may be considered in selected treatment-refractory cases, although further evidence is needed.