Introduction: Hyponatraemia following surgery is usually due to a mismatch between fluid input and output peri- and post-operatively. Syndrome of inappropriate antidiuretic hormone secretion (SIADH) is another important cause of hyponatraemia, commonest cause being medications, and intrathoracic and intracranial infections and neoplasia. SIADH has been reported to occur after pituitary surgery but rarely after other types of surgery. We present a severe case of SIADH-related hyponatraemia after minor surgery.
Case: A 70-year-old man presented to the emergency department complaining of vomiting, loss of appetite, fatigue, and abdominal discomfort. A week prior to presentation he had a transurethral resection of a bladder tumour, which was discovered during investigation for painless haematuria. He was asked to ensure adequate fluid intake post-surgery. He had a past medical history of type 2 diabetes for which he took Metformin and Simvastatin. His sodium level was normal prior to surgery. On examination his blood pressure was normal and he was clinical euvolaemic. Neurological examination was normal.
Investigations and management: Initial investigations revealed severe hyponatraemia (sodium 116 mmol/l), hypo-osmolality (234 mOsm/kg) and an inappropriately elevated urinary osmolality (577 mOsm/kg) and urine sodium level (74 mmol/l). His random cortisol rule out adrenal insufficiency and his thyroid and renal function test results were normal. He was diagnosed with acute SIADH. He was treated with concentrated sodium chloride solution (hypertonic saline) and oral fluid restriction. His serum sodium level was monitored which gradually improved over the next few days. He remains well.
Discussion: We have presented a case of SIADH with severe hyponatraemia following a minor surgical procedure. The condition may have been exacerbated by increased fluid intake post-operatively. Prompt treatment with hypertonic saline and controlled fluid intake is the mainstay of management while avoiding rapid correction of serum sodium levels which would precipitate pontine demyelination.