Abstract
In cases of Sweet's syndrome with pulmonary involvement, fever of unknown origin, and macrocytic anaemia, VEXAS syndrome can be considered in the differential diagnosis. A 67-year-old man who was taking prednisolone for a fever of unknown origin and Sweet's syndrome was referred to us because of an abnormal chest shadow. Computed tomography revealed a nonfibrotic hypersensitivity pneumonitis-like opacity, and blood test results indicated macrocytic anaemia. His pulmonary symptoms spontaneously improved but again exacerbated approximately 1 month later. Methylprednisolone pulse therapy improved his condition, but he had recurring fever flare and pulmonary involvement post-treatment. A peripheral blood UBA1 gene test planned at a specialized institution was not performed, making the diagnosis difficult. We attempted careful tapering of methylprednisolone, but his macrocytic anaemia led to pancytopenia and he unfortunately died of sepsis due to neutropenia.