Multifocal osteolytic lesions of the skeletal system are a challenge regarding diagnosis especially when multi-nucleated giant cells which are not specific for a tumour entity are found in the histological specimen. Therefore multiple differential diagnosis have to be considered such as metastases, primary malignant bone tumours, multicentric giant cell tumour of bone and brown tumours of primary hyperparathyroidism.

A 49 year old woman underwent medical investigation in an external surgical department due to right hip pain after a fall. The radiologic skeletal status surprised with multiple osteolytic pelvic lesions and one tumour in the left scapula and first histological diagnosis described a giant cell tumour of bone with malignant aspects. After confirmation of this diagnosis by a second histopathological inquiry accomplished by a bone tumor specialist the patient was transferred to our tumour centre. To exclude the differential diagnosis of brown tumours a close look on the parathormon level was done which revealed an exorbitantly high serum amount of 922.7 pg/ml (normal 15–65 pg/ml). Further examination confirmed a parathyroid adenoma. After its extirpation serum levels of parathormon decreased and two months after therapy with high dose calcium substitution radiologic controls show a decline of osteolysis with bone consolidation.

Brown tumours of hyperparathyroidism have always to be considered as a rare differential diagnosis of multiple giant cell containing tumours. The disease cannot be distinguished by the histological pattern but can very easily be excluded by normal parathormon levels. First step of therapy in brown tumours should be surgical extirpation of parathyroid adenomas or carcinomas followed by an endocrinological regime. Only failure of this treatment requires further surgical stabilisation of the bone lesions.