Thymoma associated with syndrome of inappropriate antidiuretic hormone secretion and 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.

Thymoma and autoimmunity

The thymus is a central lymphatic organ that is responsible for many immunological functions, including the production of mature, functional T cells and the induction of self-tolerance. Benign or malignant tumors may originate from the thymus gland, with thymoma being the most common and accounting for 50% of anterior mediastinal tumors. Malignancies linked to thymoma include the loss of self-tolerance and the presence of autoimmunity. In this review, we compiled the current scientific evidence detailing the various interactions between thymoma and autoimmune diseases, including myasthenia gravis, systemic lupus erythematosus, inappropriate antidiuretic hormone secretion, pure red cell aplasia, pernicious anemia, pemphigus and autoimmune thyroid diseases. In recent years, several mechanisms have been proposed to explain these interactions. Most are based on the assumption that the 'sick' thymus, like the 'normal' thymus, can generate mature T cells; however, the T cells generated by the sick thymus are impaired and thus may exert cellular autoreactivity. Here, we present several theories that may shed light on the loss of self-tolerance associated with this epithelial tumor of the thymus.

Malignant thymoma associated with myasthenia gravis, Graves' disease, and SIADH

Patients with thymoma are likely to present with associated autoimmunologic disorders. The occurrence of syndrome of inappropriate antidiuretic hormone (SIADH) attributable to thymoma is extremely rare. We herein present an extremely rare case of a 59-year-old man patient who was discovered to have malignant thymoma associated with myasthenia gravis, Graves' disease, and SIADH. He was admitted for evaluation and treatment of hyponatremia (Na 125 mEq/l). SIADH was diagnosed, and thymoma was identified as its cause. The patient was also found to have both Graves' disease and myasthenia gravis. The hyponatremia was normalized with water restriction and 3% saline therapy before thymectomy. The thymic tumor was a Masaoka stage III thymoma that resulted in direct invasion to the wall of the innominate vein, but there was no finding of invasion to other mediastinal organs. Complete thymectomy with innominate vein graft was performed. Microscopic histopathology findings corresponded to those of a mixed-type thymoma and type B2. However, immunohistochemical stain for antidiuretic hormone was negative in the tumor cells. Adjuvant radiation therapy was employed postoperatively, and the patient's postoperative recovery was uneventful. He subsequently reached a euthyroid state. And the reversal to normal sodium and osmolality levels was continued after the tumor removal without any further management for hyponatremia. The observation of this interesting case and a literature review provided us with the opportunity to explore the pathogenesis and clinical aspects of thymoma-related autoimmune and/or endocrine disorders which must be suspected in patients with thymoma.

Thymoma-associated hypocalcemic crisis

A previously healthy male was diagnosed with a malignant thymoma. During the workup, he had syncope, which was due to severe unrecognized hypocalcemia. Additional workup was suggestive of parathyroid failure. In particular, there was no evidence of autoimmune parathyroid failure due to antibodies against the calcium-sensing receptor. Literature review reveals one additional thymoma case with these clinical features of chronic hypoparathyroidism of unknown cause.

Paraneoplastic Neurologie Syndrome and Autoimmune Addison Disease in a Patient with Thymoma

A 48-year-old man with autoimmune Addison disease developed the following paraneoplastic neurologic syndromes (PNNS): limbic encephalitis, opsoclonus/myoclonus, and sensorimotor and autonomic neuropathies. An anterior mediastinal mass detected on a chest computed tomographic scan was found on resection to be a noninvasive lymphocytic thymoma. The PNNS went into remission 1 year after the thymectomy. This is the first case of thymoma associated with autoimmune Addison disease and PNNS to be described in the literature.