INTRODUCTION. since calcium assays availability in clinical practice from 1970s, the awareness of hyperparathyroidism is grown and usually patients are diagnosed before they can develop late complications, such as overt skeletal disease.

MATERIALS AND METHODS. retrospective analysis of a paradigmatic case report.

A 38-year-old woman presented to the ambulatory of rheumatology, complaining of low back pain radiating to the thighs. Clinical examination revealed dolorability of right sacro-iliac joint and limited flexion-extension of the lumbosacral spine. MRI of the lumbosacral spine revealed the presence of two lesions, respectively on the left ilium and on the right supero-anterior margin of the iliac crest, suspected with malignancy. Laboratory analysis showed hypercalcemia (total calcium 3,79 mmol/L), elevated PTH levels (PTH 1719 ng/L) and renal failure (creatinine 1,72 mg/dL). Bone densitometry performed on the femur neck showed a T-score of -2,8 DS. Ecography of the neck demonstrated the presence of an hypoechogenic nodule of 2 cm, posterior to the lower right pole of thyroid, consistent with adenoma, and a Tc-99 sestamibi scintigraphy confirmed this finding. A CT-guided biopsy of the left iliac mass showed a fibrous proliferation with osteoclastic giant cells, a picture compatible with brown tumour.

The patient underwent lower right parathyroidectomy with intraoperative PTH assays.

One year later she was asymptomatic, the pelvic lesions were decreasing and calcium, PTH and creatinine values returned into the normal range.

RESULTS AND CONCLUSIONS. brown tumours, although rare, are disabling conditions that enter into differential diagnosis with other primary or secondary bone lesions. In these cases, a simple calcium and PTH assays may rule out this diagnosis.