Background: Hyponatraemia is a frequently encountered problem in primary care. Management should be based on the cause as inappropriate treatment e.g. fluid restriction in patients with hypoadrenalism is dangerous and potentially life-threatening.
Aims: We present five cases who presented with hyponatraemia in the primary care setting, to highlight diagnostic approach and implications for management.
Case 1 - Hyponatraemia secondary to thiazide diuretic: 69-year-old lady who presented with serum sodium 121 mmol/l 10 days after being started on bendroflumethiazide. Sodium previously 139 mmol/l, improved to 134 mmol/l 10 days after stopping bendroflumethiazide.
Case 2 - SIADH due to Ca bronchus. An 88 year old man with previously uninvestigated mild stable hyponatraemia, serum sodium 130133 mmol/l for at least 3 years. Presented acutely unwell with sodium 120 mmol/l and signs of pleural effusion. Chest CT scan showed extensive inoperable bronchial carcinoma.
Case 3 - Reset osmostat and cerebral small vessel disease: An 81 year old lady with serum sodium 126134 mmol/l for several years. Normal urinary concentrating and diluting ability. Brain CT scan showed small vessel disease. Patient was managed conservatively.
Case 4 - Hyponatraemia due to fluid and electrolyte loss in high flow stoma: 83 year old lady with serum sodium persistently 126129 mmol/l following AP resection and ileostomy. Urine analysis showed maximal sodium conservation. Serum sodium normalised subsequent to reversal of ileostomy.
Case 5 - Acute hyponatraemia due to primary adrenal insufficiency: 56 year old man presented with a ten day history of diarrhoea and vomiting. Sodium 108 mmol/l and potassium 5.5 mmol/l. Subsequent in-patient investigations confirmed Addisons disease.
Summary: A proposed algorithm for the investigations and differential diagnosis of hyponatraemia in primary care is presented.
Conclusion: Hyponatraemia is not a definitive diagnosis and requires further diagnostic evaluation in order to treat appropriately.