Endocrine Abstracts

We would like to describe a case of resistant hyponatraemia. A 65-year-old Caucasian male presented to ED with a two-day history of blurred vision and transient numbness in his right hand. He was an ex-smoker with a past medical history of a transient ischaemic event in 2019 and a myocardial infarction in 2005. He admitted to a 10kg weight loss. He had no changes to his medications in the recent past which included lansoprazole, ramipril, mirtazapine, atenolol, clopidogrel, atorvastatin and isosorbide mononitrate. He used to drink eight to ten cups of tea a day and enjoyed soups. He was clinically euvolaemic with a serum sodium of 117mmol/l and urinary sodium of 83 on admission. After investigations, a diagnosis of syndrome of inappropriate of antidiuretic hormone (SIADH) was made. Mirtazapine, lansoprazole, ramipril and atenolol were stopped and he was commenced on fluid restriction. A CT chest, abdomen and pelvis was normal and his hyponatraemia persisted past the wash-out period after stopping medications. His sodium levels proved difficult to correct and he was maintained on a one litre fluid restriction four months on from diagnosis. He was intolerant to demeclocycline but had a good response to tolvaptan. A PET-CT three months after initial presentation confirmed an underlying small cell lung carcinoma (SCLC). Hyponatraemia is a common presentation on the medical take but not a common presentation for lung cancer. This case highlights the challenges of maintaining a patient on a long-term fluid restriction through patient education, considering the wash-out periods of possible offending drugs and undergoing further investigations if the clinical suspicion for malignancy is high. Hyponatraemia and the failure to normalise serum sodium both are independent negative prognostic factors in patients with malignancy. Our patient died of metastatic SCLS ten months after initial presentation having refused any chemotherapy.