Elusive cause of hypomagnesaemiaBMJ 2011; 343 doi: https://doi.org/10.1136/bmj.d5087 (Published 30 September 2011) Cite this as: BMJ 2011;343:d5087
- Krishnan Swaminathan, consultant endocrinologist 1,
- John Wilson, consultant gastroenterologist2
- 1Department of Endocrinology, Victoria Hospital, Kirkcaldy KY2 5AH, UK
- 2Department of Gastroenterology, Victoria Hospital, Kirkcaldy, UK
- Correspondence to: K Swaminathan
A 46 year old man presented with carpopedal spasm, muscle cramps, and a prolonged QTc interval on a background of a week’s history of diarrhoea and vomiting. He had a history of Barrett’s oesophagus and had been taking 40 mg omeprazole daily for many years. He had severe hypocalcaemia and hypomagnesaemia, with a corrected calcium and magnesium of 1.77 mmol/L (reference range 2.15-2.65) and 0.13 mmol/L (0.75-1), respectively. Serum parathyroid hormone was low at 3.1 ng/L (8-55). Intravenous replacement of fluids and electrolytes restored the biochemical abnormalities. He was discharged on oral alfacalcidol and magnesium glycerophosphate.
At six week follow-up, calcium had normalised (2.25 mmol/L) but symptomatic hypomagnesaemia persisted, with a serum magnesium of 0.27 mmol/L. Extensive evaluation, including upper and lower gastrointestinal endoscopy and distal duodenal biopsies, failed to identify a cause for his persistent hypomagnesaemia. He was admitted for recurrent intravenous magnesium infusions because his magnesium values were between 0.27 mmol/L and 0.29 mmol/L in spite of oral magnesium supplements. An intervention (figure⇓arrows labelled A and B) resulted in dramatic normalisation of serum magnesium values with no need for further oral or intravenous magnesium replacement.
1 What are the causes of hypomagnesaemia?
2 What interventions on the graph (indicated by the arrows) are responsible for the fluctuations in magnesium …