Chapter 18 Flashcards
What causes acondroplasia?
Activating mutation in FGFR3 (AD) where overactivation inhibits endochondrial ossification but not intramembranous bone formation (normal sized head)
Mental function, life span, and fertility are not affected
What is osteogenesis imperfecta?
Congenital defect of bone formation resulting in structurally weak bone, most commonly due to a AD defect in type 1 collagen synthesis
May present with fractures, blue sclera, and hearing loss
What is osteopetrosis?
An inherited defect of bone resorption due to poor osteoclast function resulting in abnormally thick, heavy bone that fractures easily
Most commonly due a mutation in carbonic anhydrase II leading to a loss of acidic microenvironment required for bone resorption
How might osteopetrosis present?
bone fractures
anemia, thrombocytopenia, and leukemia with extramedullary hematopoiesis due to bony replacement of the marrow
Vision and hearing impairment
Hydrocephalus due to narrowing of the foramen magnum
Renal tubular acidosis
How is osteopetrosis tx?
Bone marrow transplant
What causes rickets/osteomalacia?
Defective mineralization of osteoid (osteoblasts normally produce osteoid, which is then mineralized with calcium and phosphate to form bone) typically due to low vitD, resulting in low levels of calcium and phosphate
How is vitD activted?
25-hydroxylation in the liver and then 1,25-hydroxylaton via 1a-hydroxylase in the proximal tubule
How does vitD act?
Increases serum calcium and phosphate by acting on:
- Intestine to increase absorption of calcium and phospahte
- Kidney to increase reabsorption of both
- bone to increase resorption of both into serum
How does rickets present?
Pigeon-breast deformity-inward bending of the ribs with anterior protrusion of the sternum
Frontal bossing (enlarged forehead)- due to osteoid deposition in the skull
Rachitic rosary due to osteoid deposition at the costochondral junction
Bowing of the legs
What is osteoporosis?
Reduction in trabecular bone mass resulting in porous bone with an increased risk for fracture
Risk is based on the peak bone mass and rate of bone loss therafter
What are the most common forms of osteoporosis?
senile and postmenopausal
What are the lab findings of osteoporosis?
serum calcium, phosphate, PTH, and alkaline phosphatase are normal (helps exlcude osteomalacia which has a similar presentation but low calcium and phosphate, and increased Alk phos)
T or F. Glucocorticoids are contraindicated with osteoporosis
T. Makes worse
What causes Paget disease of bone?
LOCALIZED (not systemic) imbalance between osteoclast and osteoblast function usually occurring in late adulthood (avg. age 60+)
Etiology unknown, but possibly viral
What are the stages of Paget disease?
osteoclastic
mixed blastic-clastic
osteoblastic
With an end result of a thick, sclerotic bone that fractures easily
Describe the histo appearance of Paget disease of bone
Mosaic
How does Paget disease of bone present?
Bone pain due to microfractures
Increasing skull/hat size
- Hearing loss due to CN impingement
- Lion facies
What are the major complications of Paget disease of bone?
High-output cardiac failure
Osteosarcoma
What is osteomyelitis?
infection of marrow and bone usually occurring in children and most commonly due to bacterial infection arising from heme spread (transient bacteremia seeds the metaphysis, while open-wound bacteremia (adults) seedss the epiphysis)
What are the major causes of osteomyelitis?
S. aureus (90%)
N. gonorhoeae- sexually active adults
Salmonella-sickle cell disease
Pseudomonas- diabetics or IVDU
Pasteurella- cat or dog bites
Mycobacterium- usually Potts disease
How does osteomyelitis present?
Bone pain with systemic signs of infection (e.g. fever and leukocytosis)
Lytic focus (abscess) surrounded by sclerosis of bone on x-ray (i.e. sequestrum surrounded by involucrum)
What is avascular (aseptic) necrosis?
Ischemic necrosis of bone and bone marrow
What are the major causes of avascular (aseptic) necrosis?
Caisson disease (the bends)
Trauma/fracture
Steroids
Sickle cell
Legg-Calve Perthes Disease
What is Legg-Calve Perthes Disease?
Legg–Calvé–Perthes disease (LCPD) is a childhood hip disorder initiated by a disruption of blood flow to the femoral head. Due to the lack of blood flow, the bone dies (osteonecrosis or avascular necrosis) and stops growing. Over time, healing occurs by new blood vessels infiltrating the dead bone and removing the necrotic bone which leads to a loss of bone mass and a weakening of the femoral head. The bone loss leads to some degree of collapse and deformity of the femoral head and sometimes secondary changes to the shape of the hip socket. It is also referred to as idiopathicavascular osteonecrosis of the capital femoral epiphysis of the femoral head since the cause of the interruption of the blood supply of the head of the femur in the hip joint is unknown.
The condition is most commonly found in children between the ages of 4 and 8, but it can occur in children between the ages of 2 and 15. The main long-term problem with this condition is that it can produce a permanent deformity of the femoral head, which increases the risk of developing osteoarthritis in adults. It is also commonly known as Perthes disease, or Legg–Perthes disease. Perthes is a form of osteochondritis which only affects the hip, although other forms of osteochondritis can affect elbows, knees, ankles, and feet. Bilateral Perthes, which means both hips are affected, should always be investigated thoroughly to rule out multiple epiphyseal dysplasia.
Overview of osteoma
Benign tumor of bone, most commonly arising on the surface of facial bones and associated with Gardner syndrome
Describe osteoid osteomas
A benign tumor of osteoblasts (that produce osteoid) surrounded by a rim of reactive rim commonly occurring in young adults less than 25 yo (more common in males) and classically arising in the cortex of long bones like the femur
How might a osteoid osteoma present?
Presents as bone pain that resolves with aspirin
What should be on the Ddx for osteoid osteoma?
Osteoblastoma which is larger (2+cm, while osteoid osteomas are smaller), arise in the vertebrae, and presents as bone pain that does not respond to aspirin
Describe osteochondromas
Tumor of bone with an overlying cartilage cap (most common benign tumor of bone) arising from a lateral projection of the growth plate (metaphysis)
Can rarely transform to chondrosarcoma
Where do osteosarcomas arise?
The metaphysis of long bones, usually the distal femur or proximal tibia
What is a classic x-ray finding of osteosarcoma?
Describe giant cell tumors
Tumor composed of multinucleated giant cells and stromal cells (occurs in young adults) arising in the EPIPHYSIS of long bones, usually the distal femur or proximal tibia
“soap bubble” appearance on x-ray
Local aggressive, and may recur
What is Ewing sarcoma?
Malignant proliferation of poorly-differentiated cells derived from NEUROECTODERM arising in the diaphysis of long bones usually in males less than 15 yo
Classic ‘onion skin’ appearance on x-ray
Describe the histo of a Ewing Sarcoma
What is dermatomyositis?
Inflammatory disorder of the skin and skeletal muscle with an unknown cause (but some cases are associated with gastric carcinoma)
What are the lab findings of dermatomyositis?
Increased creatine kinase
positive ANA and anti-Jo-1 Ab
Perimysial inflammation (CD4)
Describe polymyositis
Inflammatory disorder of skeletal muscle classically seen in child-bearing women, with clinical symptoms similar to dermatomyositis but without skin involvement
Endomysial inflammation (CD8 cells)
Describe lipomas
Benign tumor of adipose tissue, most common benign soft tissue in adults
Describe liposarcomas
Malignant tumor of adipose tissue, with classic lipoblast cells
Describe rhabdomyosarcomas
Malignant tumor of skeletal muslce (most common malignant soft tissue tumor in children)
Rhabdomyoblast is the classic cell; desmin positive
Most common site is the head/neck and the vagina in young girls
