Parathyroid Disorders

Question 1

OBJ: Review and understand the basic physiology of calcium homeostasis

Answer 1

• Fractions of Calcium
  
  • Ionized- active fraction 45-50% total
  • Bound - inactive 50-55% total
  • Complexed - <1-2% total
• Parathyroid hormone (PTH) - affects ionized calcium
  
  • decreases renal calcium excretion
  • increases renal phosphorous excretion
  • Increases calcium and phosphorous mobilization from bone
  • Stimulates production of Vitamin D ⇢ increases blood calcium and phosphorous via enhanced intestinal uptake and bone mobilization

Question 2

OBJ: learn the various clinical presentations, differential diagnoses, and treatment of hypercalcemia and hypocalcemia?

Answer 2

• Hypercalcemia:
  
  • Presentation -
  • DDx -
  • Treatment -
• Hypocalcemia:
  
  • Presentation -
  • DDx -
  • Treatment -

Question 3

How is Calcium Homeostasis maintained?

Answer 3

Question 4

What are the homeostatic levels of calcium in the ECF?

Answer 4

• In healthy animals
• may be different in ill patients

Question 5

What is Primary Hyperparathyroidism?

Answer 5

• Increased PTH secretion (PTH) too high
• Hypercalcemia is characteristic

Question 6

What animals get Primary Hyperparathyroidism?

Answer 6

• More common in dogs
• rare in cats

Question 7

What are the pathologies that can cause Primary hyperparathyroidism?

Answer 7

• Adenoma
• Hyperplasia
  
  • may be bilateral
• Adenocarcinoma
• Usually solitary nodule

Question 8

What is Primary Hypoparathyroidism?

Answer 8

• Decreased PTH secretion (PTH too low)
  
  • Hypocalcemia is characteristics

Question 9

What animals suffer from Primary Hypoparathyroidism?

Answer 9

Dogs and cats - rare in both

Question 10

What is the pathology that leads to primary hypoparathyroidism?

Answer 10

• Lymphocytic parathyroiditis
• Iatrogenic damage/removal
• Parathyroid surgery

Question 11

What causes the clinical signs in Hyperparathyroidism? What are the clinical signs?

Answer 11

• Clinical signs are due to hypercalcemia
• Signs often vague and difficult to localize
• GI signs - most common in cats
  
  • anorexia
  • vomiting
  • constipation
• Renal signs
  
  • PU/PD - most common in dogs
  • Pollakiuria
• Neurologic signs
  
  • Mental dullness
  • Obtundation
  • Coma
  • Twitching
  • Muscle weakness
  • Seizures (rare)

Question 12

What other diagnoses are associated with (ionized) hypercalcemia?

Answer 12

• PTH - Dependent
  
  • Hyperparathyroidism
• PTH Independent
  
  • Hypercalcemia of malignancy
  • Vitamin D toxicity
  • Hypoadrenocorticism
  • Granulomatous diseases (e.g. fungal infection)
  • Bone lysis (e.g. osteomyelitis)
• Other disorders:
  
  • Idiopathic hypercalcemia of cats - PTH is normal
  • Chronic renal failure - occasionally with mild hypercalcemia. Increased total calcium is more common

Question 13

What Physical exam or diagnostic imagining findings are seen in hyperparathyroidism?

Answer 13

• Often normal (no specific findings)
• Neck mass - usually small; usually not palpated

Question 14

What tests exist for parathyroid evaluation?

Answer 14

• “Hypercalcemic panel”
  
  • Ionized calcium
  • PTH levels
  • PTH-rp level ⇢ PTH related peptide produced by some cancers
  • Vitamin D (Calcitriol) level

Question 15

What are the possible interpretations of the “hypercalcemic panel”

Answer 15

• Only hypercalcemic disorder with high PTH is hyperparathyroidism
• PTH is elevated in renal disease but iCa is usually normal
• PTH-rp is only elevated by neoplastic diseases
• Calcium and phosphorous show opposite changes, except in Vit D toxicity
• Parathyroid function is normal in feline idiopathic hypercalcemia

Question 16

What are the non-specific treatments for hypercalcemia?

Answer 16

• Saline diuresis - uses sodium chloride (0.9%)
• Furosemide - promotes Na loss,; give after rehydration
• Glucocorticoid - induces calcium excretion

Question 17

What are specific treatments for hypercalcemia?

Answer 17

• Bisphosphonate - Inhibit osteoclast activity; nephrotoxicity
  
  • E.x. alendronate (IV / PO) pamidronate (IV) zolendronate
• Cinacalcet - calcimimetic drugs acts at the CaSR (calcium-sensitive receptor) to decrease PTH secretion.
  
  • Undesired effects in ~65% dogs (single study)
• Calcitonin - indicated for emergency treatment of Vit D toxicity

Question 18

What is a Parathyroidectomy?

Answer 18

• Surgical removal of affected gland
• Several ablation techniques described
• Post-op monitoring of ionized calcium
• Pre-op treatment with calcitriol is sometimes given to reduce post-op hypocalcemia
  
  • no effect in a study of ~75 dogs

Question 19

What are the physiological manifestations of Hypocalcemia?

Answer 19

• Tetany - may resemble seizure
• Cardiac changes - Diminished systolic function, cardiac dilation, myocardial irritability, bradycardia, prolonged S-T and Q-T segments
• CNS dysfuntion

Question 20

What are the clinical signs of Hypocalcemia?

Answer 20

• Restlessness; neurological depression
• Seizures
• Muscle cramping (often rear legs)
• Muscle fasciculation / twitching
• Ataxia and stiff gait
• Facial and paw pruritis
• Aggression
• Panting
• Weakness

Question 21

What does hypoparathyroidism look like on a parathyroid panel? compared to hypercalcemic disorders?

Answer 21

Question 22

What is the emergency treatment for Hypocalcemia?

Answer 22

• 10% calcium gluconate - IV over 10-20 minutes
• Discontinue if bradycardia develops
• Avoid repeated IV boluses of calcium gluconate

Question 23

What is the intermediate maintenance therapy for hypocalcemia?

Answer 23

• 10% calcium gluconate given by CRI or by SQ injection
• Calcium Gluconate - preferred - MUST be diluted for SQ use
• Calcium Chloride - AVOID if possible
  
  • caustic; use with caution IV, DO NOT inject SQ

Question 24

What is the long-term maintenance therapy for hypocalcemia?

Answer 24

• Vit D2 (ergocalciferol)
• Calcitriol - Oral VIt D analogue; expense can be limitiing factor
• Oral calcium supplements - important early in treatment