22. bone pathology 3 (metabolic & inflammatory)

metabolic & inflammatory bone disease

what is osteoporosis?

• decreased bone with clinical disease

• reduction in the quantity of bone mass, the quality of which is normal

• cortical bone is reduced in thickness and increased in porosity → lacks strength and is easily fractured

osteoporosis causes

• starvation

• corticosteroids (hyperadrenocorticism)

• disuse

• aging

• intestinal parasitism (chronic, severe)

  • trichostrongylus or ostertagia infections in lambs

• calcium deficiency with normal levels of phosphorus and vitamin C

• copper deficiency (various species) → brittle bone

what is the difference between rickets and osteomalacia?

• rickets → disease of young, rapidly growing animals

• osteomalacia → disease of mature animals

rickets/osteomalacia pathology

• failure of mineralization of growth cartilage (rickets) and/or osteoid matrix (both rickets and osteomalacia)

  • rickets: abnormal endochondral ossification and defective bone formation with subsequent bone deformities and fractures

  • osteomalacia: similar to rickets but does not result in growth cartilage lesions

most common causes of rickets/osteomalacia

• vitamin D deficiency

• phosphorous deficiency

consequences of rickets/osteomalacia

• bones break easily, marrow cavity enlarged, cortex thin and spongy

• fractures on ribs, pelvis, and long bones of cattle; vertebral column of pigs

• curving of keel bone with rib fractures common in laying hens

fibrous osteodystrophy pathology

increased osteoclastic resorption of bone, which is replaced by fibrous connective tissue

• weak bones → lameness, pathologic fractures, and bone deformities

pathogenesis/causes of fibrous osteodystrophy

• primary hyperparathyroidism (rare) → high PTH production

• paraneoplastic

  • production of PTH-related protein (PTHrP)

• secondary hyperparathyroidism

  • nutritional: low Ca:high P

  • renal: usually dog with renal disease → retain P, decreased 1,25 vitamin D (→ decreased Ca absorption)

causes of bacterial/fungal osteomyelitis

• direct trauma to bone

• extension from infected soft tissue/wounds

  • actinomyces bovis

• hematogenous → metaphysis

  • trueperella pyogenes, e. coli

  • staph aureus, mycobacterium avium

  • brucella sp.

  • coccidioides immitis, blastomyces dermatiditis

pathogenesis of bacterial/embolic osteomyeltitis

• most common in young animals at metaphysis

• capillaries make sharp turn to join medullary veins → slower and less turbulent blood flow → embolus gets trapped → abscess → sequestrum