Parathyroid Pathology Flashcards
carnivore parathyroid glands
4 total
two associated with each thyroid gland (1 internal, 1 external)
horse parathyroid glands
many; difficult to find
upper: medial/dorsal to thyroid near internal carotid
lower: near thoracic inlet
ruminant parathyroid glands
near parotid and mandibular LNs
what do parathyroid glands look like histologically
pink due to being highly vascularized
hypoparathyroidism
low PTH leading to hypocalcemia
clinical signs of hypoparathyroidism
tetany/paresis (“seizures”)
dogs: tetany
ruminants: paresis (milk fever)
causes of hypoparathyroidism
- idiopathic hypoparathyroidism
- surgery
- milk fever
idiopathic hypoparathyroidism
immune mediated destruction of PTG leading to lymphocytic parathyroiditis and atrophy of the chief cells
gets replaced with fibrous tissue
how does surgery lead to hypoparathyroidism
accidental removal of PTG during a thyroidectomy
OR
intentional removal of a parathyroid adenoma
PTG adenoma –> atrophy of other PTGs
- if removed, other PTGs need time to “reactivate”
- leads to hypocalcemia after surgery
milk fever
parturient paresis/hypocalcemia
the high demand on dairy cows for milk production and fetal development leads to hypocalcemia after parturition –> paresis (downer cow)
do NOT supplement high Ca feed because will suppress PTGs with negative feedback - need to feed low Ca feed to increase demand on PTGs
hyperparathyroidism
high PTH levels leading to either hyper OR hypocalcemia
causes of hyperparathyroidism
- primary hyperparathyroidism
- secondary nutritional
- secondary renal
- humoral hypercalcemia of malignancy
primary hyperparathyroidism
functional PTG adenoma leading to excess PTH secretion
what lesion is associated with primary hyperparathyroidism
1 enlarged PTG, the rest atrophied
Ca, P, and PTH levels with hyperparathyroidism
- high Ca
- low/normal P
- high/inappropriately normal PTH
what species is primary hyperparathyroidism common in
dogs > cats
clinical signs of primary hyperparathyroidism
vomiting, anorexia, urinary calculi, constipation, PU/PD, weakness/lethargy, fibrous osteodystrophy
or NO clinical signs
is primary hyperparathyroidism associated with metastatic mineralization
no because high PTH suppresses phosphorus, so the [Ca] x [P] does not exceed 60-80
secondary nutritional hyperparathyroidism
low dietary Ca/vitamin D3 or high dietary P
what lesion is associated with secondary nutritional hyperparathyroidism
diffuse PTG hyperplasia (all 4 enlarged)
what species is secondary nutritional hyperparathyroidism common in
dogs, cats, primates, horses, birds, reptiles
clinical signs of secondary nutritional hyperparathyroidism
fibrous osteodystrophy
(“big head” in horses, “rubber jaw” in dogs)
Ca and PTH levels in secondary nutritional hyperparathyroidism
- low Ca
- high PTH
secondary renal hyperparathyroidism
CKD leads to:
1. decreased renal functional mass
2. increased FGF-23
which causes decreased activation of vitamin D3 (low calcitriol) –> decreased absorption of Ca and P from GI tract
what lesion is associated with secondary renal hyperparathyroidism
diffuse PTG hyperplasia (all PTGs enlarged)
clinical signs of secondary renal hyperparathyroidism
metastatic mineralization and fibrous osteodystrophy
what 3 locations are common sites of metastatic mineralization
kidneys
stomach lining
lung
Ca and PTH levels in secondary renal hyperparathyroidism
- low Ca
- high PTH
humoral hypercalcemia of malignancy
secretion of PTHrP from certain tumors leading to hyperparathyroidism
what species and tumor types is humoral hypercalcemia of malignancy common in
dogs, cats
lymphosarcoma, anal sac adenocarcinoma, carcinomas, sarcomas
is metastatic mineralization common in humoral hypercalcemia of malignancy
no - protective against it (similar to primary hyperparathyroidism) because it decreases P levels
Ca, P, and PTH levels with humoral hypercalcemia of malignancy
- high Ca
- low/normal P
- high PTH
C cell disorders of growth
hyperplasia, adenoma, carcinoma
what species are C cell growth disorders common in
horses
dogs
dairy bulls
what C cell growth disorder is common in dogs
C cell hyperplasia from a parathyroid tumor
PTG adenoma –> inc PTH –> hypercalcemia –> overstimulation of C cells to secrete calcitonin
what C cell growth disorder is common in dairy bulls
C cell hyperplasia OR C cell adenoma (if chronic)
dairy bulls eat high Ca diet –> overstimulation of C cells to secrete calcitonin –> hyperplasia of C cells
can become a C cell tumor if chronically overstimulated
what lesion is associated with C cell growth disorders
hyperplasia of C cells within the thyroid interstitium
