47 Disorders of the Parathyroid Gland

1. Ionized Ca (active form)

2. Protein bound (to albumin)

3. Complexed (phosphate and citrate bound Ca, may increase total Ca without affecting iCa)

Total calcium can be broken down into what categories?

Parathyroid hormone

What hormone is the major defense against fluctuations in ionized calcium?

1. inc. Ca resorption (and phosphorous excretion) in kidney

2. inc. Ca (and phosphorous) resorption mobilization in bone

3. stimulates vitamin D production to inc. Ca (and phosphorous) absorption from intestines

What places does parathyroid hormone act to increase Ca in the blood?

G:granulomatous

O:osteolytic

S:spurious

H:hyperparathyroidism (primary)

D:hypervitaminosis D

A:addison's disease

R:renal secondary hyperparathyroidism

N:neoplasia/nutrition

I:idiopathic

T:temperature (hyperthermia)

Name the pneumonic and causes/differentials for hypercalcemia:

Increase ionized Ca, decrease PTH

these are your granulomatous causes

What effect do histoplasma, blastomycosis, coccidiomycosis, and schistosomiasis have on calcium?

Anything that causes lysis of bone causes Ca to move from the bone to the bloodstream (like multiple myeloma)

How are osteolytic conditions related to calcium concentrations?

Lipemia, hemoconcentration, hemolysis

Name some spurious causes of hypercalcemia

Adenomas

What tumor commonly causes excessive secretion of PTH to cause hypercalcemia?

Cholecalciferol rodentacide that causes hypercalcemia

Name an example of a toxin that could cause hypervitaminosis D?

IONIZED Ca is NORMAL, total Ca will be increased (from the complexed Ca increase)

How does Addison's change Ca serum concentration?

Hyperphosphatemia (because kidney can't remove it) --> suppress iCa --> parathyroid hormone senses this and INCREASES PTH --> total Ca elevate, NOT IONIZED Ca

How is renal secondary hyperparathyroidism (or chronic kidney disease) related to Ca?

Lymphoma, multiple myeloma, Squamous cell carcinoma, thyroid carcinoma, AGASACA

Name a few neoplasia that can cause hypercalcemia of malignancy?

Cats

What animal is idiopathic hypercalcemia common in?

CATS: idiopathic and cancer

DOGS: primary hyperparathyroid and neoplasia

Overall, what are the top causes of hypercalcemia in cats and dogs?

4 total, 2 on R. and 2 on L. (external and internals)

How many parathyroids do animals have?

Calcitonin regulates/tones down Ca in bloodstream

What does calcitonin do to calcium?

Active Vitamin D3, INHIBITS PTH secretion, increases ionized calcium

What is calcitriol?

Calcitriol

What chemical blocks the synthesis of the PTH molecule within the gland by preventing transcription of the PTH genes?

Pulse dose

How can you prevent ionized calcium increase when you are calcitriol dosing for renal secondary hyperparathyroidism?

If Phosphorous and Calcium increase

Under what conditions should you stop calcitriol?

Even in the absence of hyperphosphatemia and hypocalcemia

Renal secondary hyperparathyroidism can develop prior to azotemia in cats even in the absence of WHAT?

Chronic kidney disease

Hyperparathyroidism and hyperphosphatemia occur frequently in dogs with what naturally occurring disease process?

Chronic kidney disease leads to phosphate retention and a decrease in calcitriol (which is active vitamin D3 made in the kidneys), and an overall decrease in ionized calcium. To compensate for these problems, the body increases PTH --> secondary renal hyperparathyroidism

What is the pathogenesis for renal secondary hyperparathyroidism?

FALSE: they do NOT, so they must get vitamin D from the diet

TRUE OR FALSE: animals (cats and dogs) photoactivate vitamin D from the sun the same way humans do.

There will be no PTH and low iCa with primary hypoparathyroid + hyperphosphatemia

What is the relationship of PTH (plasma parathyroid hormone) and serum ionized Ca to primary hypoparathyroidism?

Increased PTH and total hypercalcemia, but NOT an increase of ionized calcium (normal ionized calcium with secondary)

What is the relationship of PTH (plasma parathyroid hormone) and serum ionized Ca to secondary (renal or nutritional) hyperparathyroidism?

Increased PTH AND intracellular ionized calcium (elevated ionized calcium)

What is the relationship of PTH (plasma parathyroid hormone) and serum ionized Ca to primary hyperparathyroidism?

No PTH increase, but increased ionized calcium

What is the relationship of PTH (plasma parathyroid hormone) and serum ionized Ca to PTH independent hypercalcemia (malignancy, vitamin D toxicity)?

Malfunction of gland, like from benign adenoma

What is the typical cause of primary hyperparathyroidism in dogs?

Metabolic abnormality outside parathyroid gland --> resistance to function of PTH

What is the typical cause of secondary hyperparathyroidism in dogs?

DOGS: 10 years old, Keeshounds

CATS: 13 years old, mixed breed/siamese

What is the typical signalment of dogs and cats affected by primary hyperparathyroidism?

1. PU/PD

2. muscle weakness (potential atrophy)

3. decreased activity

4. lower urinary tract signs

note: PU/PD because Ca impairs the ability of the kidney to concentrate urine. skeletal structure is also weakened from PTH causing breakdown of bones to release Ca. increase in Ca will inc. stone formation = urinary signs

Describe the top clinical signs seen in dogs with primary hyperparathyroidism

1. lethargy

2. anorexia

3. vomiting

4. CONSTIPATION

Name the more common signs of primary hyperparathyroidism in cats

ionized calcium

Which type of calcium do you look at to differentiate forms of hyperparathyroidism?

surgical excision

What can you do if primary hyperparathyroidism is being caused by an adenoma (treatment wise)?

It is a biomarker that elevates with stages of feline chronic kidney disease

What is the point of FGF-23 in cats?

High PTH is TOXIC

What is the problem with high PTH levels?

Feeding a diet with excess phosphorous or low calcium

ideal ratio for calcium:phosphorous is 1.2:1

AVOID PURE MEAT DIETS

What nutritional problems have the ability to cause nutritional secondary hyperparathyroidism in animals?

Nutritional secondary hyperparathyroidism (because they are not getting enough calcium through the light/diet, their body produces excess PTH for bone breakdown to inc. blood calcium)

An iguana comes in because the owner is concerned about growth abnormalities. You see on radiographs there is replacement of normal bone with fibrous tissue. When talking about husbandry, you learn that the owner does not have a UV light for this animal because she is a new owner and did not know she needed one. Thoughts?

Secondary to severe magnesium depletion (you need Mg to hold onto Ca) = suppressed PTH, hypocalcemia, and hyperphosphatemia

What can cause transient hypoparathyroidism?

DOGS: females predisposed

CATS: male predisposed

What is the difference in SEX predilection between cats and dogs for primary hypoparathyroidism?

HYPOparathyroidism

A dog presents with seizures, stiff gait, muscle tetany, cramping, pain, focal muscle fasciculations, twitching, tremors, and INTENSE facial rubbing. Is this more likely to be primary hyper or hypo parathyroidism?

Hypocalcemia

Hypoparathyroidism causes hyper or hypo calcemia?

Hypocalcemia

Stiff gait, rigid abdomen, muscle fasciculations, bradycardia, and weak femoral pulses are more characteristic of primary hyper or hypo calcemia.

Primary hypoparathyroidism

If you have normal renal function, normal Vitamin D and magnesium, but persistent hypocalcemia (both total and ionized) and hyperphosphatemia, what are you thinking?

Hypocalcemia = eclampsia

What condition do you have to worry about with pregnant animals?

FIRST: Slow IV calcium gluconate

SECOND: oral supplementation of calcium and vitamin D (calcitriol)

What are the two phases for treating primary hypoparathyroidism?