Clinicians in Varese report a case of a rarely observed consequence of primary hyperparathyroidism – multiple brown tumours initially misdiagnosed as malignant osteosarcoma. Brown tumours can occur when osteoclast activity is especially high, resulting in haemorrhage and fibrosis within the bone marrow. The brown colour is imparted by a build-up of haemosiderin. For the 70-year-old patient reported in this case study, chest X-ray incidentally detected an 8cm axillary mass, showing local invasion on CT, concurrent with hypercalcaemia. Giant cell-rich osteosarcoma was high on the list of initial diagnoses. Lesions were detected elsewhere in the skeleton. However, immunohistochemistry findings were not in keeping with malignancy and, instead, demonstrated haemorrhage and haemosiderin deposition. Parathyroid hormone levels, which were then measured, were elevated. Subsequent investigations led to the discovery of a large right-sided parathyroid adenoma. The patient was therefore treated with parathyroid surgery plus denosumab to improve bone density.

The authors reflect on the unusual nature of this case, in an era when primary hyperparathyroidism is frequently detected early, before complications have developed. They also comment on the value of the histopathology input, which led to the true diagnosis. This carried a profoundly different prognosis to the more sinister conditions initially suspected.

Read the full article in Endocrinology, Diabetes & Metabolism Case Reports doi:10.1530/EDM-20-0046