MRCP2-1427

MRCP2-1427

An elderly female presents with a 2 week history of breathlessness. Her past medical history includes diet-controlled type 2 diabetes, ischaemic heart disease, hypothyroidism and depression. Her medication list includes levothyroxine, aspirin, simvastatin, ramipril, bisoprolol and citalopram. Observations on presentation to Emergency Department are as follows: respiratory rate 26/min, saturations 94% (on 4 litres oxygen via Venturi), heart rate 80 beats per minute, blood pressure 156/82 mmHg. Auscultation demonstrates crackles at the left base with no wheeze. The abdomen is soft and non-tender. There is no oedema peripherally.

Blood results on admission are provided below:

Hb 134 g/l
Platelets 172 * 109/l
WBC 13.3 * 109/l
Na+ 128 mmol/l
K+ 5.1 mmol/l
Urea 13 mmol/l
Creatinine 178 µmol/l
Serum osmolality 220 mosm/kg
Urinary sodium 50 mEq//l

What is the most likely cause of hyponatraemia in this elderly female patient?