Case Report: Eosinophilic granulomatosis with polyangiitis presenting as a multiple sclerosis mimic

Eosinophilic granulomatosis with polyangiitis (EGPA) rarely involves the central nervous system and may closely resemble inflammatory demyelinating disease. We report a 32-year-old woman with adult-onset asthma and recurrent sinusitis who presented with bilateral lower-extremity sensory symptoms and neuropathic pain. Brain and spinal magnetic resonance imaging (MRI) demonstrated multifocal T2-hyperintense lesions fulfilling dissemination in space and time according to the 2017 McDonald criteria. Cerebrospinal fluid (CSF) analysis revealed mild pleocytosis, CSF-restricted oligoclonal bands, and eosinophils on qualitative cytological examination. Multiple sclerosis (MS) was initially suspected and intravenous methylprednisolone resulted in partial improvement. Three weeks later, the patient developed palpable purpura, inflammatory arthralgia, and left foot-elevating paresis. Follow-up MRI demonstrated a new enhancing lesion and electrophysiological studies revealed axonal neuropathy. Retrospective review of the initial laboratory results showed that peripheral eosinophilia was already present at baseline, while subsequent evaluation identified eosinophilic gastritis on gastroscopic biopsy and eosinophilic bone marrow infiltration. The diagnosis of EGPA was established based on the clinical presentation, laboratory findings, and histopathological evidence of eosinophilic inflammation, and the patient fulfilled the 2022 ACR/EULAR classification criteria for EGPA. Treatment with corticosteroids and cyclophosphamide followed by maintenance mepolizumab resulted in sustained clinical stability. This case highlights that EGPA may present with radiological and CSF-findings suggestive of MS and emphasizes the importance of integrating systemic manifestations to avoid diagnostic delay.