Definition of Osteitis fibrosa:

Osteitis fibrosa is a complication of hyperparathyroidism (too much parathyroid hormone) in which the bones turn soft and become deformed.

Causes, incidence, and risk factors:

There are four parathyroid glands in the neck. They produce parathyroid hormone, which helps control calcium levels in the body. Parathyroid hormone increases the break down of bone (bone metabolism). Too much parathyroid hormone (hyperparathyroidism) can lead to increased bone metabolism, 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.