Relative importance of renal failure and increased bone resorption in the hypercalcaemia of myelomatosis.

In order to define the relative importance of renal failure and increased bone resorption in the hypercalcaemia of myelomatosis 22 untreated patients were studied, of whom 12 were hypercalcaemic. Most patients had malabsorption of radiocalcium from the gastrointestinal tract and evidence of increased bone resorption as assessed by fasting urinary hydroxyproline/creatinine ratio. The mean OHPr/Cr ratio, however, was similar in patients with and without hypercalcaemia. Renal failure and Bence Jones proteinuria occurred more frequently in the hypercalcaemic patients. In four patients with hypercalcaemia there was an increase in OHPr/Cr after saline infusion accompanied by an improvement in renal function and hypercalcaemia. Mithramycin given to the same patients further reduced hypercalcaemia, presumably by inhibiting bone resorption. It was concluded that the hypercalcaemia of myelomatosis is due to the combination of renal failure and increased bone resorption, but that the OHPr/Cr ratio in the untreated state is a poor indicator of the degree of bone resorption in hypercalcaemic patients.