Endocrine Abstracts

Low potassium and magnesium are common findings found in patients seen on acute medical take which is often not followed up.

A 23-year-old previously well Asian lady, presented with history of fatigue, weight loss and palpitations. She has been always thirsty and polyuric at night. There was history of tetany in childhood. There was a family history of an aunt who had Barter’s syndrome and her parents were first cousins.

She had low potassium (2.7–3 mmol/l) and low magnesium (0.08 mmol/l). She was normotensive. Plasma rennin activity (12.8 pmol/l per h after overnight recumbency and 25.4 pmol/l per h after 30 min upright) and aldosterone levels were high (425 pmol/l after overnight recumbency, and 1255 pmol/l after 30 min standing). She had normal serum calcium levels (2.30 mmol/l) and hypocalciuria (<0.4 mmol/day).

She was started on oral potassium 600 mg QDS and magnesium glycerol phosphate initially on 2 tablets three times daily and spironolactone 50 mg (Mg 0.27 mmol/l). She continued to be symptomatic affecting her day to day life. She was started on magnesium infusions fortnightly which improved her symptoms and magnesium levels remained at 0.5 mmol/l. Spironolactone has been switched to amiloride as it was causing polymenorrhoea and breast enlargement.

Genetic testing confirmed Gitelman syndrome (Homozygous for two SLC12A3 mutation). She was weaned off infusion by gradually increasing oral supplementation to 16 tablets in a day with magnesium remaining around 0.41 mmol/l.

Her symptoms returned with fall in magnesium levels to 0.21–0.3 mmol/l and was put back on fortnightly magnesium infusions for the last more than 3 years. Currently she is on 16 tablets of oral magnesium, 20 mg BD of Amiloride and fortnightly magnesium infusions.

Currently pre infusion magnesium levels are 0.24–0.56 mmol/l and post infusion levels are 1.5 mmol/land patient continues to be asymptomatic.

This case illustrates the need for follow up investigations for these electrolyte abnormalities.