Case Report: Here, we present the case of a 40-year-old Thai male who presented with progressive proximal muscle weakness with dysphagia, anemia, hepatosplenomegaly, and an anterior mediastinal mass. After a thorough investigation, the patient was diagnosed with stage I type AB thymoma with GM and PRCA. Following treatment with thymectomy, corticosteroids, and immunosuppressive agents, muscle weakness improved, hepatosplenomegaly resolved, and laboratory abnormalities normalized. The patient was then able to resume his normal daily activities and return to work.

Conclusion: In this case, we report a rare association of GM, PRCA, hepatosplenomegaly, and thymoma. Early detection with prompt treatment with tumor removal and immunosuppressive medications resulted in a good clinical response. Based on our review of the literature, this is the first published case report to describe this combination of coexisting conditions.

Keywords: Thymoma, Granulomatous myositis, Pure red cell aplasia, Hepatosplenomegaly, Paraneoplastic syndrome