Abstract
<title>Abstract</title> <p>Background Myelin oligodendrocyte glycoprotein antibody-associated disease (MOGAD) is a neuroinflammatory disorder of the central nervous system that can present with a cerebrospinal fluid (CSF) pleocytosis. Eosinophils in the CSF are uncommonly identified in MOGAD and true eosinophilia of > 10 eosinophils/µL or > 10% of CSF leukocyte composition has not been previously reported. Case Presentation: We describe the case of a 4-year-old male who initially presented with headache and fever followed by a seizure one week later. Initial evaluations were suggestive of meningoencephalitis due to leptomeningeal enhancement on magnetic resonance imaging (MRI) and pleocytosis on CSF analysis. He subsequently developed encephalopathy and right leg weakness two weeks later. Repeat MRI demonstrated lesions in the basal ganglia and a longitudinally extensive thoracic spinal cord lesion. CSF analysis was significant for pleocytosis with 18% eosinophils. Comprehensive infectious workup initiated due to concern for a possible parasitic infection returned negative. He was presumptively treated for a neuroinflammatory disorder with pulse intravenous corticosteroids and intravenous immunoglobulin and returned to his neurologic baseline. Subsequent testing revealed positive serum MOG antibodies (titer 1:100), confirming a diagnosis of MOGAD with an acute disseminated encephalomyelitis (ADEM) core clinical event type. Conclusions This case demonstrates that MOGAD can present as true eosinophilic meningoencephalitis, expanding the recognized laboratory spectrum of the disorder. Clinicians should consider demyelinating etiologies like MOGAD in the differential diagnosis of CSF eosinophilia, particularly when infectious and neoplastic evaluations are negative. Identifying these atypical presentations is critical for the prompt initiation of appropriate immunotherapy.</p>