14b: Calcium Homeostasis

Paired PTH and iCa⁺⁺ findings consistent with hyperPTH

High PTH with high Ca⁺⁺

T/F: normal PTH with high Ca⁺⁺ rules out hyperPTH

False, if the patient has high Ca⁺⁺ any PTH in the upper half of the reference range is considered inappropriately high

US findings consistent with hyperPTH

Large hypoechoic nodules within the thyroid gland, may not find normal parathyroid glands from negative feedback → atrophy

Three treatment options for hyperPTH

• Surgery

• Radiofrequency ablation

• Ethanol ablation

Outcomes associated with parathyroidectomy

Good outcomes, it is a straightforward surgery as long as you avoid vital structures

Radiofrequency ablation mechanism of action

Heat destroys the tissue

Ethanol ablation mechanism of action

Chemical destruction of tissue

Why might ethanol ablation be less desirable as a treatment option

May damage other vital structures nearby (vagus nerve, carotid artery) and it can be challenging to assess what an appropriate volume is

Key worry with post treatment management of hyperPTH

Concerned about hypocalcemia post treatment

If an animal is going to have a hypocalcemic crisis following treatment for hyperPTH when is it going to happen

Within 5 days

How can we avoid hypocalcemia following treatment for hyperPTH

Start on calcitriol before treatment if the patient’s iCa⁺⁺ is >1.7 mmol/L

Factor associated with likelihood of hypocalcemia after treatment for hyperPTH

The higher the Ca⁺⁺ before treatment the more likely they are to tank after treatment

CS of hypocalcemia

• Facial pruritis

• Panting

• Seizures and muscle fasciculations → hyperthermia

• Myalgia, stiff gait

• Nervous

• Anorexia, V/D

Why does hypocalcemia cause facial pruritis

Hypocalcemia → paresthesia → pruritis

Demographic for hypocalcemia caused by ecclampsia

Small mom with big litter and poor nutrition (but not always the pattern!)

How does pancreatitis cause hypocalcemia

Pancreatitis → saponification of fat → binds up Ca⁺⁺

T/F: any sick cat can have low Ca⁺⁺

True

How does hypomagnesemia cause hypocalcemia

Hypomagnesemia causes hypoPTH → low Ca⁺⁺

Primary causes of hypomagnesemia

DKA and severe intestinal disease

T/F: hypoproteinemia causes clinical hypocalcemia

False, total Ca⁺⁺ will decrease but iCa⁺⁺ should be normal

Medications/ingestions that cause hypocalcemia

• Phosphate enema

• Ethylene glycol toxicity

How do blood transfusions cause hypocalcemia

Blood products are anti-coagulated → infusion of Ca⁺⁺ deficient blood

Emergency dose of Ca⁺⁺ for hypocalcemia

1 mL/kg of 10% calcium gluconate IV slowly

What do you need to watch if giving emergency dose of calcium gluconate

Monitor ECG

Arrhythmias you need to watch for when supplementing with a lot of calcium gluconate

• Bradycardia

• VPCs

• Shortened Q-T interval

Primary cause of hypoPTH

Immune mediated destruction

Demographic for hypoPTH

Younger to middle aged female dog

Chem findings consistent with hypoPTH

Low Ca⁺⁺ and high or high-normal phosphorous

Definitive diagnosis for hypoPTH

Paired PTH and iCa⁺⁺

Paired PTH and iCa⁺⁺ findings consistent with hypoPTH

Low Ca⁺⁺ with low or low-normal PTH

Treatment for hypoPTH

Oral calcitriol

Factors that make treating hypoPTH with oral calcitriol easy

The body responds very quickly to changes in calcitriol concentrations which makes it easy to adjust if the dose is too high

Factors that make treating hypoPTH with oral calcitriol hard

Commercial tabs are too big, and we have to have it compounded which can introduce variability if we are switching between pharmacies

When do we monitor after we start treatment for hypoPTH

Check Ca⁺⁺ 3-4 days after starting treatment or changing the dose

Target parameters for hypoPTH treatment

Low normal Ca⁺⁺, keeps phosphorous at high normal

Ultimate goal of treatment for hypoPTH

Avoid CS associated with hyper or hypocalcemia