Thymoma associated good syndrome presenting with combined immunodeficiency severe neutropenia and opportunistic infection

Thymomas can disrupt normal thymopoiesis through reduced expression of the autoimmune regulator (AIRE) gene, leading to immune dysregulation and paraneoplastic syndromes such as Good’s syndrome. This rare condition is characterized by hypogammaglobulinemia, profound B-cell lymphopenia, T-cell dysfunction, neutralizing autoantibodies against cytokines such as interferon-α and interleukin-12, and increased susceptibility to opportunistic infections, particularly those caused by intracellular and encapsulated pathogens. We present the case of a 54-year-old Colombian woman with a previously unidentified anterior mediastonic mass who presented with chronic diarrhea, severe neutropenia, and mucocutaneous herpes simplex infection. Immunological evaluation demonstrated hypogammaglobulinemia (IgG 473 mg/dL), undetectable IgM (< 21 mg/dL), and an absence of circulating B cells on flow cytometry (CD19⁺ < 1%). Bone marrow flow cytometry revealed a markedly expanded CD8⁺ T cell population with an inverted CD4/CD8 ratio and a complete absence of B lymphocytes, without evidence of dysplasia or hematologic malignancy. The preserved trilineage hematopoiesis in the bone marrow biopsy suggests an immune-mediated mechanism of neutrophil destruction rather than primary bone marrow failure. Due to severe neutropenia and a high risk of infection, and following a multidisciplinary risk-benefit assessment, temporary immunomodulatory therapy was initiated with rabbit antithymocyte globulin (rATG, 3.5 mg/kg for 5 days), cyclosporine, and filgrastim, along with intravenous immunoglobulin replacement and antiviral therapy with acyclovir, to stabilize hematological parameters and allow for invasive procedures. After clinical stabilization, the patient underwent video-assisted thoracoscopic surgery with complete resection of the mediastonic mass. Histopathological analysis confirmed a type A thymoma, establishing the diagnosis of Good syndrome. Following thymectomy and the initiation of regular intravenous immunoglobulin replacement therapy, the patient has not experienced any new opportunistic infections. Good’s syndrome should be suspected in patients with thymoma presenting with hypogammaglobulinemia, inverted CD4/CD8 ratio, and opportunistic infections. This case highlights the importance of early immunological evaluation and the need for careful multidisciplinary risk-benefit assessment when considering potent immunosuppressive agents such as rATG in patients with pre-existing combined immunodeficiency. When administered with close monitoring for viral reactivation and appropriate antimicrobial prophylaxis, targeted immunomodulatory therapy may offer a viable rescue strategy for the management of severe immune-mediated cytopenias prior to definitive surgical treatment.