Hypercalcaemia in primary oxalosis: role of increased bone resorption and effects of treatment with pamidronate

Primary oxalosis is a rare congenital disorder characterised by widespread deposition of calcium oxalate crystals throughout the body. In this paper, we describe the development and treatment of hypercalcaemia associated with oxalosis in a child who had undergone renal transplantation, combined liver and kidney transplantation, and two liver retransplant procedures in the past 5 years. Hypercalcaemia occurred on three separate occasions in association with liver dysfunction due to graft rejection; renal function was not grossly impaired and serum intact parathyroid hormone levels were normal. Intravenous pamidronate therapy led to rapid normalisation of the serum calcium concentration on all three occasions. Iliac crest biopsy revealed large numbers of oxalate crystals in the bone marrow, many of which were associated with macrophages, identified using the antibody MAC 387. Bone histomorphometry demonstrated an increase in the percentage eroded surface but no increase in osteoid surface. These observations indicate that hypercalcaemia associated with oxalosis can occur in the absence of renal dysfunction and may result from excessive bone resorption, induced either directly or indirectly by macrophages surrounding oxalate crystals in the bone marrow. Pamidronate therapy was effective in restoring serum calcium to normal.