Parathyroid Pathology

Question 1

carnivore parathyroid glands

Answer 1

4 total

two associated with each thyroid gland (1 internal, 1 external)

Question 2

horse parathyroid glands

Answer 2

many; difficult to find

upper: medial/dorsal to thyroid near internal carotid

lower: near thoracic inlet

Question 3

ruminant parathyroid glands

Answer 3

near parotid and mandibular LNs

Question 4

what do parathyroid glands look like histologically

Answer 4

pink due to being highly vascularized

Question 5

hypoparathyroidism

Answer 5

low PTH leading to hypocalcemia

Question 6

clinical signs of hypoparathyroidism

Answer 6

tetany/paresis (“seizures”)

dogs: tetany
ruminants: paresis (milk fever)

Question 7

causes of hypoparathyroidism

Answer 7

1. idiopathic hypoparathyroidism
2. surgery
3. milk fever

Question 8

idiopathic hypoparathyroidism

Answer 8

immune mediated destruction of PTG leading to lymphocytic parathyroiditis and atrophy of the chief cells

gets replaced with fibrous tissue

Question 9

how does surgery lead to hypoparathyroidism

Answer 9

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

Question 10

milk fever

Answer 10

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

Question 11

hyperparathyroidism

Answer 11

high PTH levels leading to either hyper OR hypocalcemia

Question 12

causes of hyperparathyroidism

Answer 12

1. primary hyperparathyroidism
2. secondary nutritional
3. secondary renal
4. humoral hypercalcemia of malignancy

Question 13

primary hyperparathyroidism

Answer 13

functional PTG adenoma leading to excess PTH secretion

Question 14

what lesion is associated with primary hyperparathyroidism

Answer 14

1 enlarged PTG, the rest atrophied

Question 15

Ca, P, and PTH levels with hyperparathyroidism

Answer 15

• high Ca
• low/normal P
• high/inappropriately normal PTH

Question 16

what species is primary hyperparathyroidism common in

Answer 16

dogs > cats

Question 17

clinical signs of primary hyperparathyroidism

Answer 17

vomiting, anorexia, urinary calculi, constipation, PU/PD, weakness/lethargy, fibrous osteodystrophy

or NO clinical signs

Question 18

is primary hyperparathyroidism associated with metastatic mineralization

Answer 18

no because high PTH suppresses phosphorus, so the [Ca] x [P] does not exceed 60-80

Question 19

secondary nutritional hyperparathyroidism

Answer 19

low dietary Ca/vitamin D3 or high dietary P

Question 20

what lesion is associated with secondary nutritional hyperparathyroidism

Answer 20

diffuse PTG hyperplasia (all 4 enlarged)

Question 21

what species is secondary nutritional hyperparathyroidism common in

Answer 21

dogs, cats, primates, horses, birds, reptiles

Question 22

clinical signs of secondary nutritional hyperparathyroidism

Answer 22

fibrous osteodystrophy
(“big head” in horses, “rubber jaw” in dogs)

Question 23

Ca and PTH levels in secondary nutritional hyperparathyroidism

Answer 23

• low Ca
• high PTH

Question 24

secondary renal hyperparathyroidism

Answer 24

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

Question 25

what lesion is associated with secondary renal hyperparathyroidism

Answer 25

diffuse PTG hyperplasia (all PTGs enlarged)

Question 26

clinical signs of secondary renal hyperparathyroidism

Answer 26

metastatic mineralization and fibrous osteodystrophy

Question 27

what 3 locations are common sites of metastatic mineralization

Answer 27

kidneys stomach lining lung

Question 28

Ca and PTH levels in secondary renal hyperparathyroidism

Answer 28

- low Ca - high PTH

Question 29

humoral hypercalcemia of malignancy

Answer 29

secretion of PTHrP from certain tumors leading to hyperparathyroidism

Question 30

what species and tumor types is humoral hypercalcemia of malignancy common in

Answer 30

dogs, cats lymphosarcoma, anal sac adenocarcinoma, carcinomas, sarcomas

Question 31

is metastatic mineralization common in humoral hypercalcemia of malignancy

Answer 31

no - protective against it (similar to primary hyperparathyroidism) because it decreases P levels

Question 32

Ca, P, and PTH levels with humoral hypercalcemia of malignancy

Answer 32

- high Ca - low/normal P - high PTH

Question 33

C cell disorders of growth

Answer 33

hyperplasia, adenoma, carcinoma

Question 34

what species are C cell growth disorders common in

Answer 34

horses dogs dairy bulls

Question 35

what C cell growth disorder is common in dogs

Answer 35

C cell hyperplasia from a parathyroid tumor PTG adenoma --> inc PTH --> hypercalcemia --> overstimulation of C cells to secrete calcitonin

Question 36

what C cell growth disorder is common in dairy bulls

Answer 36

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

Question 37

what lesion is associated with C cell growth disorders

Answer 37

hyperplasia of C cells within the thyroid interstitium