page_title: Osteitis fibrosa cystica
section_title: Pathophysiology
hierarchical_section_title: Osteitis fibrosa cystica / Pathophysiology
caption_attribution_description: English: Brown tumours of the hands in a patient with hyperparathyroidism. Image from Radiopaedia.org case here
context_page_description: Osteitis fibrosa cystica, 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, and the formation of cyst-like brown tumors in and around the bone. Osteitis fibrosis cystica, abbreviated OFC, also known as osteitis fibrosa, osteodystrophia fibrosa, and von Recklinghausen's disease of bone, 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.
context_section_description: The effects of OFC on bone are largely dependent on the duration of the disease and the level of parathyroid hormone (PTH) produced.  PTH is responsible for maintaining a homeostatic calcium concentration in the blood.  It activates the parathyroid-hormone related protein receptor located on osteoclasts and osteocytes, both of which are responsible for the breakdown and maintaining of bone.  Abnormalities affecting the parathyroid glands cause a surplus of PTH, which, in turn, increases the activity and frequency of osteoclasts and osteocytes.  Increased PTH levels trigger the release of stored calcium through the dissolution of old bone, as well as the conservation of serum calcium through a cessation in the production of new bone.
  Generally, the first bones to be affected are the fingers, facial bones, ribs, and pelvis. Long bones, which are longer than they are wide, are also among the first affected. As the disease progresses, any bone may be affected.
caption: X-ray of the hands showing brown tumors in the long bones of the fingers
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