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| | ==[[Hyperparathyroidism]]== | | ==[[Hyperparathyroidism]]== |
| − | [[Image:parathyroidadeoma.jpg|thumb|right|100px|Parathyroid adenoma. Image courtesy of Biomed Archive.]]
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| − | ===Primary===
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| − | * Primary hyperparathyroidism is caused by glandular hyperplasia or neoplasia. [[Image:parathyroidhyperplasia.jpg|thumb|right|100px|Parathyroid hyperplasia. Image courtesy of Biomed Archive.]]
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| − | * Rare.
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| − | ===Secondary===
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| − | * Secondary hyperparathyroidism causes [[Bones Metabolic - Pathology#Hyperparathyroidism|fibrous osteodystrophy or "rubber jaw"]].
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| − | * In secondary hyperparathyroidism, the gland is overactive due to another condition coexisting in the body, rather than a primary parathyroid gland defect.
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| − | * There are two common forms of secondary hyperparathyroisism:
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| − | *# [[Parathyroid Glands - Pathology#Nutritional Hyperparathyroidism|'''Nutritional Hyperparathyroidism''']]
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| − | *#* This includes [[Parathyroid Glands - Pathology#Metabolic Bone Disease|Metabolic Bone Disease]].
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| − | *# [[Parathyroid Glands - Pathology#Renal Hyperparathyroidism|'''Renal Hyperparathyroidism''']]
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| − | * Both forms result in 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.
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| − | ** Fibrous tissue is seen around the tooth roots.
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| − | ** Bone softens in adult animals.
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| − | *** This is what gives rise to the term "rubber jaw".
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| − | *** Long bones become soft with thin cortices.
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| − | **** These fracture easily.
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| − | ====Nutritional Hyperparathyroidism====
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| − | [[Image:secondaryhyperparathyroidism.jpg|thumb|right|100px|Secondary hyperparathyroidism - "rubber jaw". Image courtesy of Biomed Archive.]]
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| − | * Nutritional hyperparathyroidism is also known as nutritional osteodystrophy.
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| − | * This occurs most commonly in:
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| − | ** Young, fast-growing animals
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| − | ** Animals with a poor diet, for example:
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| − | *** Swine fed unsupplemented cereal grain
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| − | *** Dogs and cats fed all-meat diets
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| − | *** Horses fed bran
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| − | **** In this case, nutritional hyperparathyroidism is known as "bran disease".
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| − | =====Pathogenesis=====
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| − | * Pathogenesis follows low calcium/high phosphate diets.
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| − | ** These lead to decreased serum calcium levels, stimulating [[Parathyroid Glands - Pathology#Hormonal Control|PTH]] release.
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| − | ** The increase in PTH gives an increase in bone resorption, causing pathology.
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| − | =====Pathology=====
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| − | * '''Gross'''
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| − | ** Severe cases may show:
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| − | *** Maxillary and mandibular swelling
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| − | *** [[:Category:Teeth - Anatomy & Physiology|Teeth]] lost or buried in soft tissue
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| − | *** Nasal and frontal bone enlargement, leading to dyspnoea
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| − | *** Long bone fracture
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| − | *** Detatchment tendons and ligaments
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| − | ** Early or less severe cases are characterised by shifting lameness and ill thrift.
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| − | * '''Histological'''
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| − | ** Osteoclastic resorption
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| − | ** Fibrous replacement
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| − | =====Metabolic Bone Disease=====
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| − | * Metabolic bone disease affects lizards in captivity, particularly young green iguanas
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| − | * The condition is caused by:
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| − | ** Dietary deficiency of calcium and vitamin D
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| − | *** For example, due to poor lighting (which diminishes viatmin D production).
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| − | ** Dietary excess of phosphorus
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| − | ** Certain toxicities
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| − | ** Diseases of the kidneys, [[Liver - Anatomy & Physiology|liver]] or parathyroid
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| − | *** This aetiology is rare
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| − | * Clinical signs include:
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| − | ** Lethargy
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| − | ** Inability to support weight
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| − | ** Rounded skull
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| − | ** Spontaneous fractures
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| − | ** Adult animals also show signs of [[Parathyroid Glands - Pathology#Hypocalcaemia|hypocalcaemia]]
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| − | * The skeleton shows reduced density on radiography.
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| − | ====Renal Hyperparathyroidism====
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| − | * Renal Hyerparathyroidism is mostly seen in the dog as an expression of chronic renal disease.
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| − | =====Pathogenesis=====
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| − | [[Image:renalhyperparathyroidism.jpg|thumb|right|100px|Parathyroid hyperplasia in renal hyperparathyroidism. Image courtesy of Biomed Archive.]]
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| − | # Chronic renal disease results in reduced glomerular filtration.
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| − | # As glomerular filtration is reduced, phosphate is retained. Chronic renal failure also causes inadequate vitamin D production in the kidneys.
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| − | # Hyperphosphataemia develops due to phosphate retention.
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| − | #* Hypocalcaemia also occurs, as high levels of phosphate depress calcium levels.
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| − | # PTH is released in an attempt to maintain the correct blood calcium:phosphorous ratio. This can have several effects:
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| − | #* Parathyroid hyperplasia
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| − | #** I.e. '''renal secondary hyperparathyroidism'''.
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| − | #* Soft tissue mineralisation
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| − | #** Particularly seen in dogs
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| − | #** Calcium is commonly deposited in the subpleural connective tissue of the intercostal spaces.
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| − | #** Calcification also occurs in other sites, e.g. [[Monogastric Stomach - Anatomy & Physiology|stomach]] wall, lungs, kidneys.
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| − | #* Increased bone resorption
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| − | #** This causes fibrous osteodystrophy, or "rubber jaw".
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| − | =====Pathology=====
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| − | [[Image:Renal_osteodystrophy.jpg|thumb|right|100px|"Rubber jaw" in renal osteodystrophy. Image courtesy of Biomed Archive.]]
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| − | * Pathology seen in renal hyperparathyroidism is very similar to that seen in nutritional hyperparathyroidism.
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| − | * '''Gross'''
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| − | ** The major gross presentation is a fibrous osetodystrophy, or rubber jaw.
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| − | *** The maxillae and mandible appear swollen.
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| − | *** Radiographically, bone shows reduced density, and [[:Category:Teeth - Anatomy & Physiology|teeth]] hence appear embedded in soft tissue.
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| − | *** However, only a few cases of chronic renal disease show such severe bone lesions.
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| − | ** Other lesions may also be seen.
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| − | *** Intercostal muscles may be calcified.
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| − | *** Bone marrow lesions may cause anaemia.
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| − | *** The lung may show oedema, and have calcified alveolar walls.
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| − | * '''Histological'''
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| − | ** Osteoclastic resorption
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| − | ** Fibrous replacement
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| − | [[Category:Parathyroid Glands - Pathology]]
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