Primary hyperparathyroidism presenting as a brown cell tumour of the hallux

Abstract

A 46-year-old woman, with no contributory history, presented with a 7 month growth in her right hallux. Initially, she had noticed a dark discolouration of the distal aspect of the toe, followed by a gradual non-tender swelling and subsequent eff acement of the nail (fi gure). Results of an initial biopsy suggested that it could be a brown tumour, which prompted further biochemical tests, the results of which revealed a parathyroid hormone (PTH) concentration of 154 ng/L and a serum calcium concentration of 2·67 mmol/L in the setting of normal renal function and vitamin D suffi ciency. Her 24 h urinary calcium-tocreatinine ratio did not fi t the criteria for familial hypocalciuric hypercalcaemia. Results of parathyroid scintigraphy showed a right inferior parathyroid adenoma. A dual-energy x-ray absorptiometry scan of the distal radius revealed a bone mineral density of 0·471 g/cm2 (T score –3·7; Z score –3·1). After a right inferior parathyroidectomy and a disarticulation of the distal hallux, PTH fell to 23 ng/L and serum calcium to 2·0 mmol/L. Pathology confi rmed the presence of a parathyroid adenoma and a brown tumour of the hallux. Brown tumours are a rare presentation of primary and secondary hyperparathyroidism, and arise because of excessive osteoclast activity. They are composed of mononuclear stromal cells mixed with multinucleated giant cells. Haemorrhagic infi ltrates and haemosiderin deposits within the lesion give the characteristic brown colour. All reports describing brown tumours in the setting of primary hyperparathyroidism largely involve the jaw or the long bones. We believe that this is the fi rst documentation of a brown tumour in the small bones of the foot in a patient with primary hyperparathyroidism. This case shows that brown tumours can occur in an unusual location, and that the discovery of one should prompt further investigation. Although we do not advocate checking serum PTH concentrations in every patient, we suggest that bio chemical tests, starting with serum calcium, might help to uncover the underlying cause of a suspicious lesion.