A 16-year-old male presents with lethargy. He takes no medication and has generally been otherwise
well. Examination reveals that he is obese with a BMI of 36.4 kg/m and a blood pressure of 120/72
There are no abnormalities of the cardiovascular, respiratory or abdominal systems.
Sodium 141 mmol/L (137-144)
Potassium 2.8 mmol/L (3.5-4.9)
Urea 5.6 mmol/L (2.5-7.5)
Creatinine 76 µmol/L (60-110)
Which of the following is the most likely diagnosis?
Apparent mineralocorticoid excess
Bartter’s syndrome This is the correct answer
Hypokalaemic periodic paralysis
Bartter’s syndrome is an autosomal recessive renal disorder, caused by a number of different
mutations. Presentation is often in childhood with gastrointestinal upset, failure to thrive and polyuria,
but it can present in adolescence also.
The classic abnormalities seen on bloods are hypokalaemic alkalosis and elevated renin and
aldosterone levels. The blood pressure is usually normal, and oedema is not a classic sign.
Hyponatraemia and hypochloraemia may also be present. Urinary sodium, potassium and chloride
Treatment is aimed at preventing potassium wasting, for example with spironolactone and electrolyte
supplements. Indomethacin is also effective, by inhibiting excess prostaglandin synthesis.
Apparent mineralocorticoid excess is a rare form of pseudohyperaldosteronism which is associated
with early onset severe hypertension, which is not present in this case.
In Cushing’s disease/syndrome the patient is often hypertensive rather than normotensive as
described here. Proximal muscle wasting is often marked and is often commented on in the stem in
combination with a description of the truncal obesity. This level of hypokalaemia is also unusual in
Conn’s syndrome presents with hypertension in addition to hypokalaemia and alkalosis.
Hypokalaemic periodic paralysis is a rare channelopathy characterised by intermittent weakness and
paralysis with corresponding falls in the potassium levels in the blood. The presentation described
here does not fit with this diagnosis