Osteitis fibrosa cystica

Osteitis fibrosa cystica (sometimes called "brown tumor of bone") is a rare condition that develops when the parathyroid glands make too much parathyroid hormone for a long time, usually from a parathyroid gland problem or, less often, from kidney disease that disrupts calcium and phosphate balance. The excess hormone pushes bone cells to break down bone faster than it can rebuild, leaving weak, thinned-out areas.

Over time, this constant bone breakdown can create fibrous scar-like tissue and cyst-like spaces inside the bone, sometimes with areas of bleeding that give them a brownish color under the microscope — hence the nickname "brown tumor," even though it isn't a true tumor or cancer. These spots can cause bone pain, deformity, or make a bone more likely to fracture.

Diagnosis typically involves blood tests for calcium, phosphate, and parathyroid hormone, along with imaging like X-rays or a DEXA scan to look at bone density and structure. Treatment focuses on addressing the underlying cause of the excess parathyroid hormone, which your doctor will guide based on whether it comes from a parathyroid gland issue or kidney-related disease. With appropriate medical care, affected bone areas can often heal over time.