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28th February 2025
An 86-year-old lady is referred from her care home with a 2-week history of worsening confusion and lethargy
An 86-year-old lady is referred from her care home with a 2-week history of worsening confusion and lethargy. She has a 25 pack-year smoking history and a longstanding history of cough with sputum production, although her carers think this has recently worsened. She takes regular amlodipine, simvastatin and colecalciferol, and a salbutamol inhaler taken as required.
On examination, she is pale, cachectic and drowsy. Her GCS is 13/15. There is mild generalised weakness on neurological examination, but tone, reflexes and sensation are all normal. She is euvolaemic.
Investigations:
| Haemoglobin | 96 g/L (115-155 g/L) |
| White cell count | 6.1 x 10^9/L (4.0-11.0 x 10^9/L) |
| Platelet count | 156 x 10^9/L (150-400 x 10^9/L) |
| Sodium | 115 mmol/L (137-144 mmol/L) |
| Potassium | 3.8 mmol/L (3.5-5.3 mmol/L) |
| Urea | 2.7 mmol/L (2.5-7.0 mmol/L) |
| Creatinine | 78 μmol/L (60-110 μmol/L) |
| Adjusted calcium | 2.5 mmol/L (2.2-2.6 mmol/L) |
| Glucose | 6 mmol/L (4-11 mmol/L) |
| Serum osmolality | 210 mOsmol/kg |
| Urine sodium | 39 mmol/L |
A plain CT scan of the head is normal. Peak flow readings are within normal limits.
What is the most likely cause of this lady’s hyponatraemia?
Select the SINGLE most appropriate option from the list below. Select ONE option only.
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