The Joint Annual Scientific Meetings of the Endocrine Society of Australia and the Society for Reproductive Biology 2018

Hypoparathyroidism-independent hypocalcaemia in severe hypomagnesaemia. (#262)

Walter E. Plehwe 1 , Ayesha Saqib 1
  1. The Epworth Centre, Richmond, VIC, Australia

A 77yo Caucasian female was admitted for investigation of dysphagia. Gastroscopy, biopsy and imaging revealed metastatic small-cell carcinoma of the oesophagus. Her past history included post-surgical hypoparathyroidism from early adult life after thyroidectomy for probable multinodular goitre. She was normocalcaemic (total Ca++ 2.57mmol/L, albumin 39g/L) taking calcitriol 0.25µg bd without calcium supplements.
She was treated with chemotherapy including carboplatin. She developed severe hypomagnesaemia (0.47mmol/L; N: 0.70-1.10) (a recognised complication of platinum-based drugs due to injury to the distal convoluted tubule) but also symptomatic hypocalcaemia (total Ca++ 1.40, albumin 28, corrected Ca++ 1.64). Supplementation with calcium and increased calcitriol alone was ineffective but normocalcaemia was restored with both intravenous and oral MgSO4.
Chemotherapy was continued in 3 week cycles with carboplatin on Day1 maintaining normocalcaemia with concurrent iv infusions of 10g MgSO4 followed by oral magnesium supplements. Additionally oral calcium was given days 1-7 in each cycle. She achieved a partial remission of her malignancy but then developed progressive disease requiring palliative care. She passed away 8 months after her initial presentation.
It is well-accepted that PTH secretion is magnesium-dependent. Hypomagnesaemia also induces resistance to PTH. Our patient was hypoparathyroid but normocalcaemic on presentation. Possible explanations for her hypocalcaemia include alteration of the normal heteroionic exchange of Ca++ and Mg++ at the bone surface with increased Mg++ release in exchange for increased skeletal uptake of Ca++ (1) or a possible role of Mg++ in regulation of vitamin D action in bone or gut.
Hypoparathyroidism is now an uncommon complication of thyroid surgery. However platinum-containing drugs are used commonly in chemotherapy. This case highlights the necessity to consider repletion of magnesium in patients receiving platinum especially in those with known hypoparathyroidism.

  1. Seelig M. Magnesium deficiency in the pathogenesis of disease. New York: Plenum Publishing Corporation; 1980, p278.