Endocrine calcium phosphate metabolism

Question 1

How is a drop in Ca2+ rectified by the body

Answer 1

Parathyroid glands detect this and cause release of PTH which increases uptake from bone, intestine and from urine by kidneys

Question 2

How is a rise in Ca2+ rectified by the body

Answer 2

Calcitonin is released from thyroid gland which increases calcium deposition in bone and decreases uptake from intestines and urine

Question 3

How is calcium distributed in the body

Answer 3

50% is free ionised calcium
50% is protein or complex bound

Question 4

What is PTHrP

Answer 4

A PTH like factor that mimics action of PTH and can be involved in mediating hypercalcaemia of malignancy

[Normally regulates calcium in fetus + acts in neonate due to secretion in milk]

Question 5

How many parathyroid glands are there

Answer 5

Normally 4

Question 6

How is vitamin D made active

Answer 6

gets hydroxylated in liver; then again in kidney by renal 1 alpha hydroxylase to active form

The second hydroxylation (from 25-OH-cholecalciferol) is regulated by calcium levels

Question 7

If we had very high dietary vitamin D, what intermediate would we get lots of

Answer 7

25-OH cholecalciferol since the conversion of vit D to this in liver is not regulated

Question 8

What are the two types of parathyroid dependent causes of hypercalcaemia

Answer 8

Primary hyperparathyroidism

Chronic renal failure

Question 9

Differentials of hypercalcaemia which are vitamin D dependent

Answer 9

Iatrogenic e.g cod liver oil
Plants e.g nightshade, jessamine due to containing calcitriol glycosides

Rodenticide toxicity
Anti-psoriasis creams

Question 10

What disease causes hypercalcaemia via local vitamin D production

Answer 10

Granulomatous disease e.g paniculitis

Question 11

What is the most common cause of hypercalcaemia in dogs

Answer 11

Malignancy (i.e parathyroid independent)

e.g **lymphoma, **anal sac adenocarcinoma, thymoma, **multiple myeloma, bone neoplasia (primary or metastatic)

Question 12

How can renal failure lead to hypercalcaemia

Answer 12

Decrease in phosphate excretion which stimulates parathyroid via inhibition of vit D activation (which usually inhibits parathyroid gland)

+ less renal tissue for activating vitamin D so again less inhibition on parathyroid gland

Question 13

How can hypercalcaemia cause renal failure

Answer 13

Because it is nephrotoxic to secrete large amounts of calcium

Question 14

How to tell if hyperparathyroidism is primary or secondary to renal failure

Answer 14

In renal failure, ionised calcium is usually normal or low (while total calcium may be high) vs in primary disease, ionised is high

Phosphate is high in secondary renal hyperparathyroidism but low in primary disease

Question 15

How can Cushings/addisons affect calcium handling

Answer 15

Both can cause hypercalcaemia via unclear mechanisms

Question 16

How can anti-psoriasis cream cause hypercalcaemia

Answer 16

Because it contains calciptriol/calcipotriene which is a type of vitamin D

Question 17

Treating idiopathic hypercalcaemia in cats

Answer 17

First try changing diet; increased fibre to reduce gut throughput time and reduce Ca2+ absorption, renal diets whcih are low in Ca2+

Prenisolone
Bisphosphonate can be used to inhibit osteoclastic activity so reduce Ca2+ reabsorption

Question 18

What consequences of idiopathic hypercalcaemia in cats is common

Answer 18

Chronic renal failure
Calcium oxalate urolithiasis

Question 19

Which breed is 50x more likely to get primary hyperparathyroidism

Answer 19

Keeshonden

Question 20

Clinical signs of primary hyperparathyroidism

Answer 20

PU/PD as can’t concentrate urine with hypercalcaemia (more Ca2+ and Na+ enter urine so water follows)

Muscle weakness
Inappetance
Constipation
Facial pruritis and oral discomfort due to tooth roots loosened by calcium mobilisation from jaw
Uroliths
Renal failure = rare complication

Question 21

Why might ALP be high in primary hyperparathyroidism case

Answer 21

Coming from bone due to elevated bone turnover

Question 22

Diagnosis of primary hyperparathyroidism

Answer 22

High Ca2+
High PTH but PTHrP normal
+ phosphate usually low or low/normal

Question 23

How does parathyroid gland look on ultrasound in primary hyperparathyroidism

Answer 23

Large hypoechoic nodule within thyroid

Question 24

What are the treatment options for primary hyperparathyroidism

Answer 24

Surgery
Percutaneous ethanol injection via ultrasound guidance
Heat ablation

Question 25

How to immediately treat dog presenting with hypercalcaemia

Answer 25

i.e while waiting to work out cause

Saline diuresis to encourage Ca2+ loss via kidneys
Furosemide
Bisphosphonates (inhibits osteoclast activity)
[Could try exogenous calcitonin]

Question 26

Signalment of primary hyperparathyroidism

Answer 26

Middle aged to older dogs; rare in cats
Keeshonden breed predisposed

Question 27

What do we pre-treat severely hypercalcaemic dogs with before dealing with hypercalcaemia

Answer 27

Vitamin D and calcium for 12-24 hours to stop severe hypocalcaemia after surgery/treatment

Question 28

Signs of hypocalcaemia in dogs

Answer 28

Panting and nervousness, vocalisation, aggression
Stiff, stilted gait
Muscle fasciculations
Tetanis seizures

If chronic see cataracts (punctate or linear)

Question 29

How to treat hypocalcaemia

Answer 29

IV calcium with monitoring of heart

Question 30

What are the risks with subcut calcium injection

Answer 30

Thrombophlebitis, skin necrosis and sloughing

Question 31

Common causes of canine hypocalcaemia

Answer 31

Hypoalbuminaemia
Renal failure
Acute pancreatitis
Eclampsia
Hyerpthyroidism
UTI

Other options: hypoparathyroidism which may be primary or after treatment for hyperparathyroidism
Toxic e.g ethylene glycol
Iatrogenic after phosphate enema, sodium bicarbonate in fluid therapy

Question 32

How can magnesium deficiency alter calcium handling

Answer 32

Magnesium is essential for PTH release so deficiency can lead to functional hypoparathyroidism