Progressive peripheral CD8+ T lymphocytosis complicated by pure red cell aplasia following immunosuppressive therapy for thymoma-associated myasthenia gravis

Autoimmune disorders and paraneoplastic syndromes in thymoma

Thymomas are counted among the rare tumour entities which are associated with autoimmune disorders (AIDs) and paraneoplastic syndromes (PNS) far more often than other malignancies. Through its complex immunological function in the context of the selection and maturation of T cells, the thymus is at the same time highly susceptible to disruptive factors caused by the development and growth of thymic tumours. These T cells, which are thought to develop to competent immune cells in the thymus, can instead adopt autoreactive behaviour due to the uncontrolled interplay of thymomas and become the trigger for AID or PNS affecting numerous organs and tissues within the human body. While myasthenia gravis is the most prevalent PNS in thymoma, numerous others have been described, be they related to neurological, cardiovascular, gastrointestinal, haematological, dermatological, endocrine or systemic disorders. This review article sheds light on the pathophysiology, epidemiology, specific clinical features and therapeutic options of the various forms as well as courses and outcomes of AID/PNS in association with thymomas. Whenever suitable and backed by the limited available evidence, the perspectives from both the thymoma and the affected organ/tissue will be highlighted. Specific issues addressed are the prognostic significance of thymectomy on myasthenia gravis and other thymoma-associated AID/PND and further the impact and safety of immunotherapies on AID and PND relating to thymomas.

Peripheral blood T lymphocytosis in thymoma: an insight into immunobiology

PURPOSE

Peripheral blood T lymphocytosis (PBTL) is a rare, yet poorly understood manifestations of thymoma, which is postulated to be linked with autoimmune/paraneoplastic manifestations such as myasthenia gravis (MG), pure red cell aplasia (PRCA), etc.; more commonly encountered in this neoplasm.

METHOD

We aim to describe the flowcytometric immunophenotypic data of PBTL in a 43-year-old male; 6 months after successful completion of chemoradiotherapy (CT/RT) for a large, invasive, and metastatic type B1 thymoma; and present a comprehensive review of all such cases reported over last 42 years (N = 21) (1977-2019).

RESULT

A larger size of the tumors (≥ 10 cm), presence of local invasion and/or distant metastasis, and type B (cortical or lymphocyte rich) histology were more likely to be associated with PBTL. Tumors associated with MG/PRCA (N = 9/21) tend to have lower PBTL compared to those without such manifestations; and PBTL subsided following thymectomy with or without CT/RT. Immunophenotypic analysis of PB revealed a CD8 +  > CD4 + mature (naïve) polyclonal T cells resembling late cortical thymocytes.

CONCLUSION

Thymic intratumoral microenvironment might influence occurrence PBTL that may have a pathophysiologic link to development of autoimmune manifestations. Immunophenotypic characteristics of peripheral blood lymphoid cells should be the clue for accurate characterization and to avoid a misdiagnosis of a lymphoproliferative neoplasm.