A Case in which Eosinophilic Meningoencephalitis Occurred during Oral Corticosteroid Tapering and after Switching from Anti-IL-5 to Anti-IgE Treatment

A 49-year-old man with severe eosinophilic asthma, sinusitis, and esophagitis was admitted with a sudden severe headache. The patient was diagnosed with eosinophilic meningoencephalitis based on frontotemporal abnormalities on brain magnetic resonance imaging and high eosinophil counts in the cerebrospinal fluid. His allergic-disease control levels were poor, requiring regular oral corticosteroid (OCS) use. He was switched from anti-interleukin (IL)-5 to anti-IgE therapy because of worsening urticaria and asthma symptoms during OCS tapering. We suspect this was a case of complex eosinophilic meningoencephalitis caused by the combination of OCS tapering and anti-IL-5 therapy cessation that acquired anti-IgE antibody sensitization based on positive drug-induced lymphocyte stimulation test results.