successful in filling the lesions caused by OFC. A report showed that in 8 out of 11 instances where cavities caused by OFC were filled with transplanted bone, the lesion healed and the transplanted bone blended rapidly and seamlessly with the original bone. Prognosis Almost all who undergo parathyroidectomy experience increased bone density and repair of the skeleton within weeks. Additionally, patients with OFC who have undergone parathyroidectomy begin to show regression of brown tumors within six months. Following parathyroidectomy, hypocalcaemia is common. This results from a combination of suppressed parathyroid glands due to prolonged hypercalcaemia, as well as the need for calcium and phosphate in the mineralization of new bone. Thirty percent of patients with OFC-like tumors caused by metastatic parathyroid carcinoma who undergo surgery see a local recurrence of symptoms. The post-surgical survival rate hovers around seven years, while patients who do not undergo surgery have a survival rate of around five years. Epidemiology Osteitis fibrosa cystica has long been a rare disease. Today, it appears in only 2% of individuals diagnosed with primary hyperparathyroidism, which accounts for 90% of instances of the disease. Primary hyperparathyroidism is three times as common in individuals with diabetes mellitus. The hospitalization rate for hyperparathyroidism in the United States in 1999 was 8.0 out of 100,000. The disease has a definite tendency to affect younger individuals, typically appearing before the age of 40, with a study in 1922 reporting that 70% of cases display symptoms before the age of 20, and 85% before 35. Primary hyperparathyroidism, as well as OFC, is more common in Asiatic countries. Before treatment for hyperparathyroidism improved in the 1950s, half of those diagnosed with hyperparathyroidism saw it progress into OFC. Rates of OFC increase alongside cases of unchecked primary hyperparathyroidism. In developing countries, such as India, rates of disease as well as case reports often mirror those published in past decades in the developed world. The other 10% of cases are primarily caused by primary hyperplasia, or an increase of the number of cells. Parathyroid carcinoma accounts for less than 1% of all cases, occurring most frequently in individuals around 50 years of age (in stark contrast to OFC as a result of primary hyperparathyroidism) and showing no gender preference. Approximately 95% of hyperparathyroidism caused by genetic factors is attributed to MEN type 1. This mutation also tends to affect younger individuals. History The condition was first