First reported case of thymoma‐associated multiorgan autoimmunity induced by COVID‐19

Thymoma‐associated multiorgan autoimmunity (TAMA) presents with skin symptoms similar to those of graft‐versus‐host disease (GVHD), liver dysfunction, and enteritis, in the absence of a history of hematopoietic stem cell or bone marrow transplantation. TAMA is a type of paraneoplastic syndrome associated with thymoma. Its etiology is unclear but is thought to be a result of breakdown of immune tolerance. Histopathologically, TAMA is characterized by epidermal acanthosis with parakeratosis, individual cell keratinization, liquefaction degeneration, and intraepidermal infiltration of CD8‐positive lymphocytes. A 64‐year‐old female patient with a history of myasthenia gravis and thymoma treated with prednisolone (10 mg/day) and cyclosporine (150 mg/day) experienced erythema on her trunk after coronavirus disease 2019 (COVID‐19) onset. A psoriatic drug eruption was suspected and the possible causative drug was discontinued, but the skin rash failed to improve. A skin biopsy demonstrated GVHD‐like histopathological findings. Diarrhea, abdominal pain, and duodenal perforation occurred concurrently, leading to the diagnosis of TAMA. Thereafter, the patient continued prednisolone and cyclosporine in the same doses as the TAMA treatment and added topical steroids. During the disease course, candida fungemia and cytomegalovirus infection developed, resulting in the patient's death. The TAMA was considered to have been caused by the release of inflammatory cytokines, autoreactive T cell activation, and regulatory T cell dysfunction induced by COVID‐19.