[Severe eosinophilic granulomatosis with polyangiitis-related peripheral neuropathy after the cessation of mepolizumab. A case report].

A 78-years-old man was treated for asthma and pansinusitis for >5 years, and mepolizumab was initiated two years previously. Two months after the cessation of mepolizumab treatment, the asthma symptoms worsened and acute progressive muscle weakness and sensory disturbance developed. On day 8 after the onset of weakness and hypoesthesia, the patient presented with complete flaccid tetraplegia and diffuse hypoesthesia of all extremities, without paresthesia or pain, and was admitted to our hospital. Blood tests revealed eosinophilia without anti-neutrophil cytoplasmic antibody elevation. Nerve conduction studies revealed severe axonal polyneuropathy and multifocal absent F-waves. Cerebrospinal fluid was normal. Eosinophilic granulomatosis with polyangiitis (EGPA) and Guillain-Barré syndrome (GBS) were suspected, and high-dose methylprednisolone was administered, followed by oral prednisolone. Eosinophils rapidly disappeared; however, the neurological symptoms did not improve. On day 16, sural nerve biopsy revealed myelinated fiber loss in most of the fibers in every nerve bundle regardless of fiber size, while eosinophilic infiltration in the epineurium and findings suggestive of necrotizing vasculitis were not observed. The results did not fulfill the pathological criteria for EGPA but supported the changes in vasculitis; hence, EGPA was diagnosed. Intravenous immunoglobulin, azathioprine, and rituximab were administered, and the prednisolone dose was gradually reduced to 10 ‍mg/d. The eosinophil count increased to 50/μl without pneumonia recurrence or worsening asthma. Neuropathy in the upper limbs gradually improved over two years, whereas that in the lower limbs did not change. This is the first reported case of sequential exacerbation of asthma and onset of EGPA after mepolizumab discontinuation. Among patients with asthma, the cessation of mepolizumab treatment may lead to the development of EGPA with an atypical clinical course, such as rapidly progressive severe neuropathy mimicking GBS.