Syndrome of Inappropriate Secretion of Antidiuretic Hormone due to Malignant Thymoma

Abstract

The authors present the case of a 51-year-old female with a syndrome of inappropriate secretion of antidiuretic hormone (SIADH) due to a malignant thymoma. Laboratory examinations of the patient showed hyponatremia, plasma hypoosmolarity in the presence of concentrated urine and normal urine excretion of sodium. CT revealed a mass lesion in the mediastinum. A biopsy of the mediastinal mass was performed and the diagnosis of thymoma with SIADH was established. This is a rare description of a malignant thymoma associated with SIADH.

Malignant Thymoma Associated with Myasthenia Gravis, Graves' Disease, and SIADH

“…T h e e p i t h e l i a l c e l l s c a n b e r e c o g n i z e d b y t h e i r l a r g e r n u c l e i wi t h p a l e c h r o ma t i n a n d s ma l l n u c l e o l i ( a r r o w) . (2,4) and one case associated with SIADH and myasthenia gravis (5).…”

Thymoma and autoimmunity

“…Other immune-mediated cytopenias, such as thrombocytopenia and neutropenia, were also reported to occur in combination with thymoma. 15 The syndrome of inappropriate antidiuretic hormone secretion has been recently linked to autoimmune mechanisms 24 and thymic tumors. Several cases demonstrated syndrome of inappropriate antidiuretic hormone secretion codiagnosed with a mass lesion in the mediastinum 24 or with MG associated with thymoma; 25 however, the mechanisms underlying this connection remain to be elucidated.…”

Lanreotide therapy in a case of thymic neuroendocrine carcinoma associated with syndrome of inappropriate antidiuretic hormone secretion

“…The most common causes of SIADH comprise: lung malignancy (small cell lung carcinoma in particular, found in up to 15% of patients) [8], neoplasms of the gastrointestinal tract, lymphomas, as well as other pulmonary disease: pneumonia, tuberculosis, lung abscess, and central nervous system disorders (tumour, infection, intracranial haemorrhage, brain injury). There are also cases of this syndrome associated with thymic carcinoma [9] and thymoma [10] found in the medical literature. Moreover, SIADH may be an adverse effect of several medications.…”