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A 56-year-old woman was diagnosed with IgA myeloma and treated with Z-DEX regimen (idarubicin + dexamethasone) and high-dose melphalan. She achieved a complete serological response, and bone marrow biopsy 3 months later showed no increase in plasma cells, but persistent paratrabecular reticulin fibrosis and an occasional large trabecular resorption cavity containing osteoclasts. She continued to receive monthly infusions of pamidronate without vitamin D or calcium and was commenced on thalidomide maintenance treatment. The patient remained seronegative, but her renal function continued to deteriorate without identifiable cause. A repeat marrow examination for increasing anaemia revealed progressive osteoclastic activity with increased bone destruction, and increasingly disordered structure with paratrabecular fibrosis but without significant plasmacytic infiltrate, appearances compatible with osteitis fibrosa cystica (figures).

A grossly elevated parathormone level of 76·9 pmol/l confirmed the diagnosis of secondary hyperparathyroidism, most likely due to the patient's continuing renal impairment, compounded by chronic mild hypocalcaemia as a result of continuous intravenous bisphosphonate prophylaxis. She was commenced on vitamin D, resulting in normalisation of the serum calcium. She later died of progressive myeloma without having suffered any skeletal event.

Despite the extensive use of bisphosphonates, osteitis fibrosis cystica is an uncommon finding in bone marrow biopsies for myeloma. Vitamin D supplementation should be considered in those patients who show persistently low calcium levels prior to monthly bisphosphonate prophylaxis.