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Brown tumours of hyperparathyroidism are seldom seen in the lower limb.
A man of 56 was seen at the orthopaedic clinic with a 3-4 year history of bilateral knee pain. This was worsening, and the knee had become swollen. On examination there was retropatellar tenderness and the patello-femoral joint was painful on movement. Abnormal bony architecture was seen on plain radiography (Figure 1). While awaiting an MRI scan he received physiotherapy, which exacerbated the pain. The MRI scan (Figure 2) showed multiple bone lesions, lobulated masses of low signal, in the lower femora. There was also breakthrough of the cortex. The menisci and cruciates were normal. The changes were consistent with a lymphatic or vascular abnormality, but all the blood tests (including myeloma screen and bone profile) were normal apart from a high serum calcium, 3.42 mmol/L. Vitamin D metabolites and 24-hour urinary calcium were not measured. The patient had noticed a swelling on the right side of his mandible and was referred to the oral and maxillofacial team. On plain radiography there was a radiolucency between the two premolar teeth, and biopsy showed a brown tumour of hyperparathyroidism. The parathyroid hormone concentration was 553 mmol/L (normal range 10-70). On ultrasonography there was no evidence of a mass lesion in the neck. A skeletal survey was not performed.
Neck exploration, undertaken by the general surgical team, revealed a 2 cm diameter left parathyroid adenoma, which was completely excised; a normal parathyroid gland was also excised. Postoperatively the patient became hypocalcaemic, and needed intravenous calcium. Oral calcium and vitamin D supplements were also prescribed. At follow-up serum calcium had stabilized at 2.20 mmol/L, alkaline phosphatase was normal, the bony symptoms had completely resolved, and plain radiographs of the femora showed resolution of the previous abnormalities.
Brown tumours of bone or osteitis fibrosa cystica (von Recklinghausen's disease of bone) are a feature of longstanding hyperparathyroidism. Microscopically, there is a combination of osteoblastic and osteoclastic activity, with associated cyst formation. Giant cells, haemosiderinladen macrophages and fibroblasts fill the lytic lesions. These are not neoplasms and the brown appearance results from vascularity, haemorrhage and haemosiderin. They also contain fibrous tissue.
The earliest bony changes in hyperparathyroidism are seen in radiographs of the hands, where subperiosteal erosions can be detected in the phalanges, especially on the radial aspect of the middle phalanx and terminal tufts. The skull acquires a mottled appearance with lucent cystic areas (‘pepperpot skull’).
In retrospect, the lesion in our patient's knee was probably a brown tumour, though a biopsy was not done. Brown tumours are now rare in the UK because biochemical assays allow early diagnosis of hyperparathyroidism. The usual sites of these lesions are the ribs, clavicles, pelvic girdle and facial bones1 and the presentation may be a pathological fracture. The lower limb is seldom affected. Lloyd2 describes the case of a 14-year-old boy with genu valgum, apathy, chorea, ataxia and hypercalcaemia. Osteitis fibrosa cystica was seen in the metaphyses of both femora, and iliac crest biopsy showed brown tumour.
In Asia the condition is more commonly encountered. From India, Mishra et al.3 report 20 patients with primary hyperparathyroidism and brown tumours in the spine, pelvis and lower limbs, some associated with spontaneous fractures. These patients had a low mean age (38 years) and showed vitamin D deficiency with low bone mineral density. The authors postulate that, in these Indian patients, deficiency of vitamin D contributed to the pathogenesis of primary hyperparathyroidism.