Osteitis fibrosa cystica ( OSS-tee-EYE-tis fy-BROH-sə SIS-tik-ə) is a skeletal disorder resulting in a loss of bone mass, a weakening of the bones as their calcified supporting structures are replaced with fibrous tissue (peritrabecular fibrosis), and the formation of cyst-like brown tumors in and around the bone. Osteitis fibrosis cystica (OFC), also known as osteitis fibrosa, osteodystrophia fibrosa, and von Recklinghausens disease of bone (not to be confused with von Recklinghausens disease, neurofibromatosis type I), is caused by hyperparathyroidism, which is a surplus of parathyroid hormone from over-active parathyroid glands. This surplus stimulates the activity of osteoclasts, cells that break down bone, in a process known as osteoclastic bone resorption. The hyperparathyroidism can be triggered by a parathyroid adenoma, hereditary factors, parathyroid carcinoma, or renal osteodystrophy. Osteoclastic bone resorption releases minerals, including calcium, from the bone into the bloodstream, causing both elevated blood calcium levels, and the structural changes which weaken the bone. The symptoms of the disease are the consequences of both the general softening of the bones and the excess calcium in the blood, and include bone fractures, kidney stones, nausea, moth-eaten appearance in the bones, appetite loss, and weight loss. First described in the nineteenth century, OFC is currently detected through a combination of blood testing, X-rays, and tissue sampling. Before 1950, around half of those diagnosed with hyperparathyroidism in the United States saw it progress to OFC, but with early identification techniques and improved treatment methods, instances of OFC in developed countries are increasingly rare.
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.