Osteitis fibrosa is a complication of hyperparathyroidism in which the bones turn soft and become deformed.

The parathyroid glands are four glands in the neck that help control calcium use and removal by the body. They do this by producing parathyroid hormone, or PTH. PTH helps control calcium, phosphorus, and vitamin D levels within the blood and bone.

Too much parathyroid hormone (hyperparathyroidism) can lead to increased bone break down, which can cause bones to turn soft.

Rarely, parathyroid cancer may cause osteitis fibrosa.

Before 1950, about half of people diagnosed with hyperparathyroidism had osteitis fibrosa. Now it is uncommon, because patients with hyperparathyroidism are diagnosed earlier, before bone softening has occurred.

People with severe hyperparathyroidism have a higher risk for developing osteitis fibrosa.