Massive atelectasis by mucoid impaction in an asthma patient during treatment with anti‐interleukin‐5 receptor antibody

Benralizumab is an interleukin‐5 (IL‐5) receptor α‐directed cytolytic monoclonal antibody that reduces rapid and nearly complete depletion of eosinophils by enhancing antibody‐dependent cell‐mediated cytotoxicity. The depletion of eosinophilic inflammation is expected to reduce mucus hypersecretion and mucoid impaction. A 75‐year‐old non‐smoking female had been treated for uncontrolled bronchial asthma with multiple drugs. Treatment with benralizumab was initiated after the asthma attack; however, four months later, she developed massive atelectasis in the left lung leading to the tracheal deviation, to the extent that nasal high‐flow therapy was required. The laboratory data showed elevated neutrophil count, whereas blood eosinophils were almost completely depleted. The thick mucus was removed by bronchofiberscopy and the atelectasis was completely resolved. No exacerbation has been observed for nine months after discontinuation of benralizumab and initiation of erythromycin. This is the first documented case that developed atelectasis by mucoid impaction during treatment with anti‐IL‐5 receptor antibody.