Effective Use of Mepolizumab in a Rare Case of Eosinophilic Granulomatosis With Polyangiitis Complicated by Pulmonary Tuberculosis

A 58-year-old woman was referred to our institution for infiltration shadows in the left upper lobe and a positive polymerase chain reaction for <i>Mycobacterium tuberculosis</i> (<i>Mtb</i>). She had worsening pain and sensory abnormalities in both lower legs. Red skin rashes were observed on both lower legs, which had resolved at the time of referral to our institution. She received oral prednisolone (PSL) monotherapy (10 mg/day) for these symptoms from her previous physician. She had a history of asthma and chronic rhinosinusitis. The nerve conduction studies and blood tests revealed mononeuritis multiplex and abnormally elevated peripheral eosinophil counts. She was diagnosed with eosinophilic granulomatosis with polyangiitis (EGPA) complicated by pulmonary tuberculosis (TB). The PSL dose was increased from 10 mg/day to 50 mg/day (1 mg/kg/day), and anti-TB treatment was initiated. Mepolizumab, a monoclonal antibody targeting interleukin-5, was also administered. Peripheral eosinophil counts were decreased, and her pain and sensory abnormalities were improved. Mepolizumab inhibited eosinophilic inflammation without compromising predominant immune function against <i>Mtb</i>. In the present case, mepolizumab was effective in treating EGPA and preventing pulmonary TB exacerbation. This is a valuable report suggesting the crucial role of mepolizumab in combined cases of both conditions.