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** Fibrous replacement
** Fibrous replacement
==From musculoskeletal==
*Can arise in a number of ways but single common factor is elevated PTH
*Results in increased resorption of bone and replacement by fibrous connective tissue
=====<u>'''Primary hyperparathyroidism'''</u>=====
*This is increased production of PTH not related to calcium or phosphorus levels
*Due to parathyroid neoplasia or bilateral idiopathic parathyroid hyperplasia
*Rare
=====<u>'''Secondary hyperparathyroidism'''</u>=====
*Regardless of pathogenesis, the result is:
**Increased osteoclastic resorption of bone and deposition of fibro-osteoid matrix that fails to mineralise
**Flat bones of the skull swell, including maxillary and nasal bones
**Long bones become soft with thin cortices which fracture easily
[[Image:Renal osteodystrophy.jpg|right|thumb|100px|<small><center>Renal osteodystrophy (Image sourced from Bristol Biomed Image Archive with permission)</center></small>]]
*'''Renal hyperparathyroidism'''
**Pathogenesis:
***[[Kidney Renal Failure - Pathology#Chronic|Chronic renal failure]]
****-> Retention of phosphate (due to reduced glomerular filtration) and inadequate production of vitamin D by kidneys
*****-> [[Kidney Renal Failure - Pathology#Uraemia|Hyperphosphataemia]] and hypocalcaemia (high P depresses Ca)
******-> Increased PTH output
*******-> Increased bone resorption
********-> '''Fibrous osteodystrophy''' - increased osteoclastic resorption of cancellous and cortical bone + proliferation of fibrous tissue
**Mainly in dogs
**Affects whole skeleton but mainly skull
**Bones soft and pliable
**Canine teeth easily removed - rubber jaw
**Microscopically - ''Osteodystrophia fibrosa'' (above = fibrous osteodystrophy) +/- [[Bones Metabolic - Pathology#Osteomalacia|osteomalacia]]
*'''Nutritional hyperparathyroidism''' (nutritional osteodystrophy)
**Also called '''fibrous osteodystrophy, “rubber jaw”''' or '''“bran disease”'''
**More common in young, fast-growing animals
**Pathogenesis:
***Low calcium / high phosphate diets
****-> Decreased calcium levels in serum
*****-> Parathyroid gland stimulated (may become enlarged)
******-> Increased PTH
*******-> Increased bone resorption
**Caused by poor diet
***Cattle and sheep - usually mild disease
***'''Swine''' fed un-supplemented cereal grain, usually mild disease
***'''Dogs/cats''' fed all-meat or offal diets (Ca:P often as high as 1:20)
****Few weeks after weaning
****Provision of calcium alone correct the problem
****Very brittle bones -> sponataneous fractures
****Extreme porosity of the whole skeleton on radioghraphs
***'''Horses''' fed bran
****Very susceptible to high phosphorus diet
****Any time after weaning, susceptibility declines after seventh year
****Early signs:
*****Mild changes of gait
*****Stiffness
*****Transient shifting lameness
****Advanced signs:
*****Swelling of mandible and maxilla - 'Big head'
*****Dyspnoea caused by swelling of nasal and frontal bones
*****Teeth lost or buried in softened jaw
*****Fractures from mild trauma
*****Detached tendons and ligaments
*****Histologically:
******Marked loss of bone
******Replacement by proliferative tissue
****Often called '''''Osteodystrophia fibrosa'''''
[[Category:Bones - Metabolic Pathology]]
[[Category:Parathyroid Glands - Pathology]]
[[Category:Parathyroid Glands - Pathology]]
[[Category:To Do - Clinical]]