13 - Bone III Flashcards
What are metabolic bone diseases?
- Generalized or systemic disease of bone caused by various reasons
- *osteodystrophy: ‘bad bone growth’
- Unclear why there are different forms
What can metabolic bone disease be caused by?
- Nutritional deficiencies or imbalances
- Hormonal deficiencies or excesses
- Toxicities
What are the 3-4 types of metabolic bone disease?
- Osteoporosis
- Osteomalacia and rickets
- Fibrous osteodystrophy
What is osteoporosis?
- Most common metabolic bone disease
- Reduction in bone density or quality
- Remaining bone is normally mineralized
What do the lesions of osteoporosis include (2)? What is the result?
- Reduction in trabecular bone with a corresponding increase in medullary cavity
a. Due to large SA available for resorption - Reduced thickness and increased porosity of cortical bone
*bone of decreased density: more brittle and easily fractured
What are the causes of osteoporosis?
- Calcium deficiency
- Starvation/malnutrition
- Lactation (following pregnancy)
How does calcium deficiency cause osteoporosis?
- Increased demand for circulating calcium=increased secretion of PTH=increase bone resorption
- *seen in cattle and sheep
What does PTH do?
- Promotes release of Ca from bone by activating osteoclasts and inhibiting osteoblasts
- Indirectly promotes increased intestinal absorption of Ca
- Promotes renal tubular reabsorption of Ca and increased renal excretion of phosphates
How does starvation cause osteoporosis?
- Lack of energy, protein and minerals
- *seen in grazing animals
How dose lactation cause osteoporosis?
- Due to inadequate calcium supplementation during pregnancy and lactation
- *seen in gilts
What are some less common causes of osteoporosis?
- Primary or secondary copper deficiency
- Hyperadrenocorticism
o Chronic glucocorticoid therapy - Physical inactivity or disuse
Osteopenia
- Bone deficiency
- Reduced amount of bone
o Does not consider the quality of remaining bone=DIFFERS from osteoporosis
Osteoporosis vs. osteopenia (humans)
- Osteoporosis: clinical condition of postmenopausal women defined by decrease BMD (disease that resulted from the osteopenia)
- Osteopenia: decrease in BMD without clinical disease
Osteomalacia vs. rickets
- Osteomalacia: disease of mature skeleton
- Rickets: disease of growing skeleton
What are the 2 causes of Osteomalacia and rickets?
- Vitamin D deficiency
- Phosphorus deficiency
What is the primary lesion of osteomalacia?
- Inadequate mineralization of osteoid leading to abnormally SOFT BONE
o Leads to deformed bones and fractures - Mature animals: defective mineralization is limited to osteoid formed during remodeling
What are the lesions of rickets?
- Also include defective mineralization of cartilage and osteoid at site of endochondral ossification
o Results in irregular thickening of physes that is most severe in most rapidly growing physes (and enlarged costochondral junctions)
What are the roles of Vitamin D?
- Increase Ca levels in ECF by promoting absorption of Ca in intestines with PTH
- Mobilization of Ca from bone
- Reabsorption of calcium by kidneys
- Promote absorption of phosphorus in intestines
What do the gross changes in Rickets depend on?
- Severity of disease (malacia)
- Duration of disease
- Stresses on individual bones
o Those that bear weight=more likely to deform
What is fibrous osteodystrophy?
- Result of prolonged bone resorption and its replacement with fibrous tissue
- Produces swelling and weakening of affected bones
What can fibrous osteodystrophy cause?
o Lameness
o Deformities
o Infractions
o Pathological fractures
What is osteodystrophy most commonly the result of?
- hyperparathyroidism (primary or secondary)
What is hyperparathyroidism?
- Any condition associated with prolonged elevation of circulating PTH
- Primary and secondary
Primary hyperparathyroidism
- Uncontrolled and excessive release of PTH from parathyroid tissue
- *characterized by hypercalcemia
- Rare in domestic animals
What kind of cases is primary hyperparathyroidism seen in (2)?
- Parathyroid gland neoplasia
- Idiopathic parathyroid gland hyperplasia
Secondary hyperparathyroidism
- Stimulus to decrease serum calcium AND
- Compensatory increased production and secretion of PTH
- *relatively more common in domestic animals: nutritional or renal in origin
What is secondary hyperparathyroidism usually characterized by?
- low-normal serum calcium concentration (normocalcemia) OR
- less commonly: mild hypocalcaemia or mild hypercalcemia
Nutritional secondary hyperparathyroidism
- Growing animals diets with deficient calcium and relatively high phosphorous
- *can get a BIG HEAD: mass of fibrous tissue (fibrosis osteodystrophy)
- *cattle and sheep develop osteoporosis
What kind of diets in pigs cause nutritional secondary hyperparathyroidism?
- All grain diet
What kind of diets in horses cause nutritional secondary hyperparathyroidism?
- Cereal hay (ex. oats, barley)
- Large amounts of grain or bran
What kind of diets in dogs and cats cause nutritional secondary hyperparathyroidism?
- All meat (‘organ meat’)
Renal secondary hyperparathyroidism
- Kidney doesn’t function properly (chronic, severe, renal disease)
o Decreased GFR: increase serum phosphorus (‘mass law’)
o Phosphorus will bind to calcium and deposited in soft tissues
Decreased serum Ca=increased PTH - *older dogs and cats
What is the pathogenesis of renal secondary hyperparathyroidism (renal osteodystrophy)?
- Loss of glomerular function
- Inability to excrete phosphate
- Hyper-phosphatemia
- *phosphate reacts with Ca and promotes hypocalcemia
o Ca-P products precipitates in soft tissues - *also get impaired vitamin D metabolism
- *uremia promotes bone resorption and poor mineralization
Osteopetrosis (marble bone disease) is a term used as a
- Syndrome or disease
- Morphologic diagnosis (descriptive term)
What is osteopetrosis?
- Abnormally dense bone in the diaphysis and metaphyses due to DEFECTIVE RESORPTION OF IMMATURE BONE
- *marble bone disease
Osteopetrosis as a disease can be seen in and is a result of
- People and animals
- Genetic defect in osteoclast production or function
- Ex. angus calves, Peruvian Paso foals (osteoclasts are ‘upside down’), lab strains of mice
Bovine calf: osteopetrosis
- Incompatible with life=still born
- Impacted molars: all arising from same site
- Short mandible
- *really dense bone=no bone marrow cavity
o Continuous columns of bone: never have been modeled or remodeled
Peruvian Paso foal: osteopetrosis
- Born alive, but have bones that fracture more easily than normal
- Recognized during investigation of spontaneous fractures
- *develops b/c the resorptive surface of osteoclasts face away from bone surface
Why is it believed that osteopetrotic bone is subject to fractures?
- Weaker, immature, woven bone is NEVER replaced by stronger, mature lamellar bone
- Microdamage is NOT properly repaired
- Bones do not model in response to biomechanical forces placed on them
In which animals does acquired osteopetrosis or osteopetrosis-like lesions occur?
- Those with severe growth retardation lattices
- Claves with BVD infections
- Cats with leukemia virus infections
- Variable degree in congenitally hypothyroid foals
What does aseptic (free of infection) necrosis of bone refer to?
- Ischemic necrosis of bone or infarction
o Ischemia=result of loss of blood supply
What are some causes of aseptic necrosis of bone?
- Legg-Calve-Perthe’s disease
- Neoplasia (including lymphoma)
- Other
Legg-Calve-Perthe’s disease
- Kids and small dogs
- Ischemic necrosis of head of femur
- Articular cartilage is spared=may contine to proliferate and become thickened if endochondral ossification is not complete at time of onset of ischemia
o May become revascularized=allows for removal of dead bone, deposition of new bone or BOTH
o Turnover may lead to collapse of articular surface - *underlying cause and pathogenesis not fully understood
What does chronic Legg-Calve-Perthe’s disease result in?
- Degenerative joint disease
Calf with lymphosarcoma (LSA)
- Irregular pale areas in bone
o Pale=due to extra lymphocytes in marrow have lead to collapse of blood vessels due to increased pressure
*not the sarcoma
Osteitis
- Inflammation of bone OR of a bone (ex. pedal osteitis)
Osteomyelitis
- Inflammation of bone and bone marrow OR
- Inflammation of bone with involvement of the metaphysis or medullary cavity
Periostitis
- Inflammation of periosteum
What often causes osteitis and osteomyelitis?
- Bacteria
- Fungi, protozoa and viruses can be involved
How might a bacteria locate in a bone?
- Direct introduction during traumatic event
- Extension from soft tissue
- Extension from a bacterial arthritis
- Hematogenously
What is osteomyelitis often characterized by?
- Chronic disease
- Necrosis and removal of necrotic bone and production of new bone
o *2 processes proceed simultaneously
Hematogenous osteomyelitis
- *Neonatal farm animals (young piglets, calves and folas)
o Lack of colostrum - Common
- Metaphyses of LONG bone and vertebrae
o Can be in any capillary bed with bone
Lumpy jaw
- Caused by Actinomyces bovis
o Enters mandible through breaks in oral mucosa - Pyogranulomatous inflammation (bone loss and bone production)
Metaphyseal osteopathy
- Aka hypertrophic osteodystrophy
- Young, large and giant breed DOGS
- Cause unknown
- *most recover spontaneously
What happens to affected dogs with metaphyseal osteopathy?
- Lame and febrile
- Swollen, painful metaphyses of long bones
Lesions of metaphyseal osteopathy (gross or radiographic)
- Periosteal new bone over metaphyses
- Lines of increased and decreased bone density adjacent and parallel to physes
Lesions of metaphyseal osteopathy (histologically)
- Suppurative inflammation and necrosis of metaphyseal bone and marrow
o Not often as it is self-limiting and usually get better on their own in 7-10 days
