physiology of hypercalcemia

Question 1

explain calcium homeostasis

Answer 1

• parathyroid hormone provides negative feedback about iCa
• PTH. increases when calcium is low and decreases when high
• active vitamin D3 (calcitriol) (activated in the kidney) and promoted ny PTH/inhibited by FGF-23

Question 2

list physiological issues that can cause hypercalcemia

Answer 2

• increase PTH activity (primary hyperthyroidism)
• activity of PTH like substances (humoral hypercalcemia of malignancy)
• increased vitamin D activity (dietary/toxin or via granulomas)
• osteolysis (local destruction of bone)
• other/unclear mechanisms (hypoadrenocorticism, feline idiopathic hypercalcemia, raisin tox)

Question 3

what is PTH related protein

Answer 3

• identical biological activity as PTH
• peptide hormone shares 60% homology with PTH
• not dedtected by PTH assay
• produced by cartilage, bone, muscle, epithelium, CNS, or specific tumour

Question 4

list principle differentials for hypercalcemia

Answer 4

Parathyroid dependent:
- parathyroid adenoma
- parathyroid adenocarcinoma
- parathyroid hyperplasia
- calcium sensor defect

parathyroid independent
- humoral hypercalcemia of malignancy
- vitamin D excess
- granulomatous disease
- osteolysis
- feline idiopathic hypercalcemia
- hypoadrenocorticism
- raisin tox
- angiostrongylus

Question 5

list further differentials for hypercalcemia that are PTH independent

Answer 5

malignancy
- lymphoma (tcell)
- anal sac apocrine gland adenocarcinoma
- other carcinoma
- myeloma
- osteosarcoma
- bone metastases
- histiocytic neoplasia

vitamin D excess
- over supplementation
- incorrect dietary formulation
- rodenticide
- vitamin D analogue
- plants
- granulomatous disease

Question 6

what are 2 mneumonics for remembering the ddx for hypercalcemia

Answer 6

HARDIONS
- hyperparathyroid
- addisions
- renal
- vitamin D
- idiopathic
- osteolysis
- neoplasia
- spurious
HOGSINYARD
- hyperparathyroidism
- osteolysis
- granulomatous disease
- spurious
- idiopathic
- neoplasia
- young
- addisons
- renal
- vitamin D tox

Question 7

list causes of hypercalcemia in dogs in oder of decreasing prevalence (most importat to least)

Answer 7

• malignancy
• hypoadrenocorticism
• primary hyperparathyroidism
• chronic renal failure
• vitamin D toxicosis
• granulomatous disease

Question 8

list causes of hyperCa in cats in order of ddecreasing prevalence

Answer 8

1. idiopathic hypercalcemia
2. renal failure
3. malignancy
4. primary hyperparathyroidism

Question 9

list causes of hyperCa in horses in order of decreasing prevalence

Answer 9

1. chronic renal failure (renal calcium excretors who use passive intestinal absorption of Ca)
2. vitamin D tox (ingestion of plants and grass containing 1,25diydroxy vitamin D like compounds)
3. hypercalcemia of malignancy
4. primary hyperparathyroidism

Question 10

list clinical signs of hypercalcemia

Answer 10

• PU/PD (Ca interferes with ADH action)
• weakness, depression, mental dullness (decreased excitability of muscular and nervous tissue)
• anorexia, vomiting, constipation (decrease excitability of GI smooth muscle and CNS influence)
• muscle twitching, shivering, seizures
• bradycardia, cardiac arrhythmias (increase contractility but decreased excitability in myocardiac muscle)

Question 11

how would you investigate hyperCa

Answer 11

Hx:
- diet
- supplements
- unusual or unfamiliar brand changes
- access to grapes/raisins
- access to vitamin D
- rodenticide ingestion
- psoriasis medication ingestion
- certain plant ingestion

signalment
- primary hyperparathyroidism is a middle age to geriatric disease
- breed disposition (esp keeshounds

clinical review
- lymph node palpation/imaging
- anal sac masses via rectal exam or imaging
- other masses - neoplasia or granulomas
- angiostrongylus

Question 12

how do we test for hyperCa

Answer 12

• total calcium
• ionised calcium (to prove genuinely physiologic
• phosphorus
• PTH
• PTHrP
• vitamin D

Question 13

what are clinical features of hypervitaminosis D

Answer 13

• increased Ca x P product causes soft tissue mineralization
• vomitin, anorexia and lethargy
• acute PU/PD and renal failure
• dysrhythmias
• seizures
• death

Question 14

discuss idiopathic hypercalcemia

Answer 14

• young to middle age cats
• mild to moderate hypercalcemia
• no obvious etiology
• hyperCa (total and ionized)
• normal phosphorus concentration
• intact PTH normal or decreased
• PTHrP undetectable
• normal vitamin D3 concentration