Unaccountable severe hypercalcemia in a patient treated for hypoparathyroidism with dihydrotachysterol.

This report describes a forty-seven-year-old female patient with a complex medical history. She was suffering from an unspecified interstitial lung disease, papillary thyroid carcinoma which had been treated, hypoparathyroidism after thyroidectomy for which she was receiving dihydrotachysterol and calcium, and atrial fibrillation and congestive heart failure as a result of mitral stenosis. Shortly after mitral valve replacement she developed a severe hypercalcemia (serum calcium 5.95 mmol/l) during a febrile illness. At that time anti-tuberculous agents were also being administered for presumed tuberculosis. The possible mechanisms for this severe elevation of the calcium level are discussed. Immobilization, while Paget's bone disease was present, and perhaps enhanced activation of dihydrotachysterol by rifampicin, could have led to increased calcium-release into the circulation. Continuous supplecation of calcium and vitamin D, provoked dehydration and the mechanism of the milk-alkali syndrome also contributed to this extremely high calcium level. It is concluded that hypoparathyroid patients being treated with vitamin D and calcium should be carefully monitored in the case of an intercurrent illness or a change in medication.