MISCELLANEOUS BONE DISORDERS
Avascular necrosis (or aseptic necrosis and osteonecrosis) is the term used for isch-emic necrosis of bone and bone marrow. Causes include trauma and/or fracture (most common); idiopathic; steroid use; sickle cell anemia; Gaucher disease; and cais-son disease. Avascular necrosis can be complicated by osteoarthritis and fractures.
Osteitis fibrosa cystica (or von Recklinghausen disease of bone) is seen when exces-sive parathyroid hormone (hyperparathyroidism) causes osteoclast activation and generalized bone resorption, resulting in possible bone pain, bone deformities, and fractures.
• Seen commonly in primary hyperparathyroidism
• Excess parathyroid hormone may be produced by parathyroid adenoma or parathyroid hyperplasia
• Can be resolved if hyperparathyroidism is treated
Microscopic exam shows excess bone resorption with increased number of osteo-clasts, fibrous replacement of marrow, and cystic spaces in trabecular bone (dissect-ing osteitis). “Brown tumors” are brown bone masses produced by cystic enlargement of bones with areas of fibrosis and organized hemorrhage.
Hypertrophic osteoarthropathy presents with painful swelling of wrists, fingers, ankles, knees, or elbows.
• Seen in the setting of bronchogenic carcinoma (a paraneoplastic syndrome), chronic lung diseases, cyanotic congenital heart disease, and inflammatory bowel disease
• Can regress if underlying disease is treated
Pathologically, the ends of long bones show periosteal new bone formation, which can produce digital clubbing and often arthritis of adjacent joints.
Osgood-Schlatter disease is a common cause of knee pain in adolescents. It develops when stress from the quadriceps during rapid growth causes inflammation of the proximal tibial apophysis at the insertion of the patellar tendon. Permanent changes to the knees (knobby knees) may develop. The lesion is not usually biopsied.
Fibrous dysplasia presents with painful swelling, deformity, or pathologic fracture of involved bone (typically ribs, femur, or cranial bones), usually in children and young adults. GNAS gene mutations cause osteoblasts to produce fibrous tissue (microscopically, irregularly scattered trabelculae) rather than bone.
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