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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.
* In secondary hyperparathyroidism, the gland is overactive due to another condition coexisting in the body, rather than a primary parathyroid gland defect.
* There are two common forms of secondary hyperparathyroisism:
* There are two common forms of secondary hyperparathyroisism:
*# [[Parathyroid Glands - Pathology#Nutritional Hyperparathyroidism|'''Nutritional Hyperparathyroidism''']]
*# [[Hyperparathyroidism#Nutritional Hyperparathyroidism|'''Nutritional Hyperparathyroidism''']]
*#* This includes [[Metabolic Bone Disease]].
*#* This includes [[Metabolic Bone Disease|Metabolic Bone Disease]].
*# [[Parathyroid Glands - Pathology#Renal Hyperparathyroidism|'''Renal Hyperparathyroidism''']]
*# [[Hyperparathyroidism#Renal Hyperparathyroidism|'''Renal Hyperparathyroidism''']]
* Both forms result in increased osteoclastic resorption of bone and deposition of fibro-osteoid matrix that fails to mineralise.
* Both forms result in increased osteoclastic resorption of bone and deposition of fibro-osteoid matrix that fails to mineralise.
** Flat bones of the skull swell.
** Flat bones of the skull swell.
=====Pathogenesis=====
=====Pathogenesis=====
* Pathogenesis follows low calcium/high phosphate diets.
* Pathogenesis follows low calcium/high phosphate diets.
** These lead to decreased serum calcium levels, stimulating [[Parathyroid Glands - Pathology#Hormonal Control|PTH]] release.
** These lead to decreased serum calcium levels, stimulating [[Parathyroid Glands - Anatomy & Physiology#Hormonal Control|PTH]] release.
** The increase in PTH gives an increase in bone resorption, causing pathology.
** The increase in PTH gives an increase in bone resorption, causing pathology.
=====Pathology=====
=====Pathology=====
** Osteoclastic resorption
** Osteoclastic resorption
** Fibrous replacement
** Fibrous replacement
=====[[Metabolic Bone Disease]]=====
=====Metabolic Bone Disease=====
* Metabolic bone disease affects lizards in captivity, particularly young green iguanas
* The condition is caused by:
** Dietary deficiency of calcium and vitamin D
*** For example, due to poor lighting (which diminishes viatmin D production).
** Dietary excess of phosphorus
** Certain toxicities
** Diseases of the kidneys, [[Liver - Anatomy & Physiology|liver]] or parathyroid
*** This aetiology is rare
* Clinical signs include:
** Lethargy
** Inability to support weight
** Rounded skull
** Spontaneous fractures
** Adult animals also show signs of [[Hypocalcaemia|hypocalcaemia]]
* The skeleton shows reduced density on radiography.
====Renal Hyperparathyroidism====
====Renal Hyperparathyroidism====
* Renal Hyerparathyroidism is mostly seen in the dog as an expression of chronic renal disease.
* Renal Hyerparathyroidism is mostly seen in the dog as an expression of chronic renal disease.