Metabolic Bone Disease

Question 1

Osteoporosis

Answer 1

Clinical disease to reduce bone mass

Question 2

Osteopenia

Answer 2

reduced bone mass without clinical disease

Question 3

Causes of osteoporosis

Answer 3

humans–estrogen loss at menopause
animals–protein calorie malnutrition; low calcium with normal phosphorus diets (usually experiemental in mammals); localized due to disuse

Question 4

Pathogenesis of osteoporosis–post menopausal

Answer 4

increased resorption due to loss of protective effect of estrogen; formation is normal or decreased

Question 5

Ovariectomy and osteopenia

Answer 5

ovariectomy induces osteopenia mostly in animals with monthly estrous cycles–so does NOT affect ovariectomized dogs and cats

Question 6

Pathogenesis protein calorie malnutrition

Answer 6

decreased formation due to overall anti-antibolic effects of malnutrition; normal resorption

Question 7

Pathogenesis localized disuse

Answer 7

Increased resorption and decreased formation.

Osteocytes sense mechanical use and signal osteoblasts concerning what bone mass they think is appropriately needed

Question 8

Structural Changes

Answer 8

• *Less bone: thin, less connected and fewer trabeculae (in long appendicular bones of adults) –trabecular bone should span from epiphysis to metaphysis–increased porosity of cortices and thin cortices in advanced stages
• *Increased microcracks
• *pathologic fractures

Question 9

Clinical Consequences of Osteoporosis/osteopenia

Answer 9

• -Pathologic fractures=force to fracture was not as high as is necessary to fracture normal bone
• -bone pain

Question 10

What is Osteomalacia/Rickets

Answer 10

Failure of mineralization in adults=osteomalacia

Failure of mineralization of bone and growth plate in young=rickets

Question 11

Causes of Osteomalacia/rickets

Answer 11

Vitamin D deficiency

phosphorus deficiency

xenobiotics that inhibit mineralization

Question 12

Pathogenesis of osteomalacia/rickets

Answer 12

Inadequate calcium/ phosphorus product at the mineralization site

vitamin D metabolites needed at mineralization site or just for calcium absorption from intestine??

Inhibition of mineralization process by drugs

Question 13

Structural changes with osteomalacia/rickets

Answer 13

accumulation of osteoid (young/adult)

retention of chondrocytes in the growth plate due to failure of mineralization

deformity due to bone softness

accumulation of microcracks secondary to reduced ability to remodel bone because unmineralized surfaces are resistant to osteoclasis

pathologic fracture

Question 14

Retention of chondrocytes in growth plate (osteomalacia/rickets)

Answer 14

causing flaring of the metaphysis due to the thickened growth plate and failure of osteoclasts to taper the bone at the cut back zone OSTEOCLASTS CAN ONLY BIND TO AND RESORB MINERALIZED BONE MATRIX

Question 15

Clinical consequences of osteomalacia/rickets

Answer 15

1) deformity
2) pathologic fracture
3) Bone Pain

Question 16

Fibrous osteodystrophy (FOD)

Answer 16

response of bone pathologic levels of PTH

Question 17

Causes of FOD

Answer 17

PTH stimulates osteoclastic bone resorption and fivrous differentiation and hyperplasia of osteoprogenitor cells

Question 18

Stuctural changes with Fibrous osteodystrophy

Answer 18

1) less than normal bone mass
2) dimensions may be reduced due to bone resorption or increase. due to proliferation of fibrous/fibro-osseous tissue in the marrow spaces and periosteum by osteoprogenitor cells
3) bone may be pliable due to bone loss and replacement with fibrous tissue
4) pathologic fractures/deformity

Question 19

Clinical consequences of Fibrous osteodystrophy

Answer 19

• -deformity
• -pathologic fracture
• -bone pain