Methods: A 77 year old female patient was admitted for the evaluation of hyponatremia and a generalized papulous exanthema with severe pruritus. Methods: The syndrome of inappropriate antidiuretic hormone secretion (SIADH) could be diagnosed as cause for hyponatremia. Biopsy of a soft tissue tumor revealed a T-cell lymphoma with widespread skelettal dissemination. Methods: Chemotherapy caused a rapid response and improvement of general well-being. SIADH could be controlled by the specific vasopressin-2-receptor antagonist tolvaptan.

Conclusions: In this patient, both the papulous exanthema and the SIADH are regarded as T-cell-lymphoma-associated paraneoplastic syndromes.