Osteitis fibrosa cystica (OFC) is a disorder involving the bone which is resulted from excessive production of parathyroid hormone (PTH) due to parathyroid gland hyperactivity. It was first described by Recklinghausen in 1891. Bone changes are a late presentation of hyperparathyroidism. Bone involvement in hyperparathyroidism has shown a significant decrease in incidence over the past decades (from 80% to as low as 15%). This fact might be due to the early detection of asymptomatic cases via serum calcium monitoring. PTH induces osteoclast activity which results in a bone break down. Hyperparathyroidism (PHP) might be due to parathyroid adenoma (up to 85% of cases), parathyroid hyperplasia, parathyroid carcinoma, renal osteodystrophy, and hereditary factors. Up to 5% of PHP cases develop OFC which can indicate a prolonged or more severe disease.
Osteitis fibrosa cystica presents as bone pain and characteristic radiologic findings including subperiosteal bone resorption in middle phalanges and distal radius, thinning of distal clavicle, bone cyst formation, “salt and pepper” pattern of the skull, brown tumor involving long bones and generalized osteopenia (up to 5% of cases). Brown tumors are caused by bone demineralization due to osteoclast activation, microfractures, and microhemorrhages. Its name comes from characteristic color resulting from hemosiderin deposition. OFC and its radiologic findings are more common in cases with parathyroid carcinoma compared to benign causes of PHP.