G. Mlawa, L. Fraser, S. Price, R. Green, B. Turner, R. Guy

 Basingstoke & North Hampshire NHS Foundation Trust  UK


BACKGROUND: Hyponatraemia is the commonest electrolyte abnormality in clinical practice, and may be a biochemical manifestation of different diseases including malignancy. About 14% of hyponatremia in medical inpatients is due to underlying tumour related conditions. The tumours most commonly resulting in hyponatremia of the syndrome of inappropriate anti-diuretic hormone secretion (SIADH) type are lung, breast and head and neck tumors. Uterine neuroendocrine tumours causing hyponatraemia are rare and can cause a diagnostic challenge as demonstrated in this case report.

We present a case of 68 years widow who was referred by her General Practitioner with  3 weeks history of   nausea, occasional vomiting, confusion, increased urinary frequency, and urinary incontinence but no dysuria. She also complained of chronic constipation, and weight loss. Her past medical history included left knee arthroscopy, cochlea implant and sterilisation in 1976.  She was non smoker but her husband was a heavy smoker. On admission to the medical admission unit she was haemodynamically stable with normal observations. Blood test revealed profound hyponatraemia (Na+ 118 mmol/l), and serum osmolarity of 247mOsm/kg, urine osmolarity of 701 mOsm/kg, urinary sodium of 110 mmol/l, random cortisol of 542 nmol/l, in keeping with SIADH. Tumour markers were negative. Her chest x-ray was unremarkable but abdominal ultrasound revealed a uterine heterogeneous enhancing mass which was also confirmed on staging CT of chest, abdomen and pelvis. Flexible sigmoidoscopy was normal. Her medications included Paracetamol and Codeine Phosphate. She was started on fluid restriction of 750mls/24hrs. She remained hyponatraemic  (116-117 mmol/l) despite this. Oral  Demeclocycline 300mg TDS was added, but she was unable to tolerate it and she was changed to tolvaptan ( 30mg od). She was discharged home on tolvaptan ( 30mg) and was reviewed by gynaecology team  in outpatient clinic; cervical biopsy histology showed a high grade neuroendocrine malignant tumour confirmed by positive immuno labelling for chromogranin, AE1/3 and CAM5.2. She is currently undergoing chemotherapy and still on tolvaptan.  Her sodium remains low but at safer levels of 127-130 mmol/L.

DISCUSSION:Hyponatraemia secondary to uterine neuroendocrine tumours is rare and  generally associated with chemotherapy treatment rather than being related to the uterine neuroendocrine tumour. Conventional treatment for hyponatraemia due to SIADH was ineffective or not tolerated. Tolvaptan treatment was more successful even though it is mainly used in patient with mild to moderate euvolaemic hyponatraemia. This case report demonstrates the possibility of using tolvalptan in severe hyponatraemia.