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