Hyponatraemia in adults — KFP-style written assessment

KFP 1 (10 marks)

A 71-year-old woman presents after two falls in a month. Bendroflumethiazide started eight weeks ago for hypertension. Sodium 126 mmol/L, potassium 3.4 mmol/L, creatinine normal. Her daughter reports increasing 'fogginess'.^{[4] [2]}

1. What is the most likely diagnosis and what evidence quantifies the drug's role? (3) ^[4]
2. Outline your immediate management plan. (4) ^{[4] [2]}
3. Which complication of her chronic hyponatraemia likely contributed to the falls? (3) ^[2]

Model answers

1. Thiazide-induced hyponatraemia. Population cohort data: 2-year hyponatraemia incidence 3.83% with bendroflumethiazide versus calcium-channel-blocker comparators, with hazard ratios of 3.56 (CI 2.76-4.60) in the first 30 days; risk differences rose with age and comorbidity. Her timeline (eight weeks), age, and the fogginess fit the classic presentation exactly. ^[4]
2. Stop the bendroflumethiazide and switch antihypertensive class (ACE inhibitor/ARB or calcium-channel blocker); check paired osmolalities and urine sodium to confirm the pattern; review other culprits (SSRIs, carbamazepine); repeat sodium within days to confirm recovery trajectory; assess falls risk (gait, vision, home hazards); monitor BP after the switch. Severe symptoms would mandate hospital assessment, but lethargy and falls with sodium 126 in the community follow the switch-and-monitor pathway. ^{[4] [2]}
3. Mild chronic hyponatraemia associates with cognitive impairment, gait disturbances, and increased rates of falls and fractures — her fogginess and the two falls fit this pattern directly, and it reverses with sodium recovery. ^[2]