Persistent COVID-19 improved with immunoglobulin replacement therapy in Good's syndrome.

A 69-year-old man with a history of thymoma resection was diagnosed with COVID-19 pneumonia. Initially, the patient responded well to molnupiravir, but he experienced a relapse. Subsequent steroids for COVID-19-related organizing pneumonia (OP) led to temporary improvement, but his condition deteriorated when the steroids were tapered off. Further investigation revealed hypogammaglobulinemia, and Good's syndrome (GS) was diagnosed. Immunoglobulin replacement therapy was administered, significantly improving the pulmonary shadows, and no subsequent relapse occurred. GS is an immunodeficiency condition associated with thymoma. If COVID-19 recurs or is refractory despite steroid therapy for OP, COVID-19 itself may not be resolved due to immunodeficiency.