Parathyroid Disorders Flashcards
OBJ: Review and understand the basic physiology of calcium homeostasis
- 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
OBJ: learn the various clinical presentations, differential diagnoses, and treatment of hypercalcemia and hypocalcemia?
- Hypercalcemia:
- Presentation -
- DDx -
- Treatment -
- Hypocalcemia:
- Presentation -
- DDx -
- Treatment -
How is Calcium Homeostasis maintained?
What are the homeostatic levels of calcium in the ECF?
- In healthy animals
- may be different in ill patients
What is Primary Hyperparathyroidism?
- Increased PTH secretion (PTH) too high
- Hypercalcemia is characteristic
What animals get Primary Hyperparathyroidism?
- More common in dogs
- rare in cats
What are the pathologies that can cause Primary hyperparathyroidism?
- Adenoma
- Hyperplasia
- may be bilateral
- Adenocarcinoma
- Usually solitary nodule
What is Primary Hypoparathyroidism?
- Decreased PTH secretion (PTH too low)
- Hypocalcemia is characteristics
What animals suffer from Primary Hypoparathyroidism?
Dogs and cats - rare in both
What is the pathology that leads to primary hypoparathyroidism?
- Lymphocytic parathyroiditis
- Iatrogenic damage/removal
- Parathyroid surgery
What causes the clinical signs in Hyperparathyroidism? What are the clinical signs?
- 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)
What other diagnoses are associated with (ionized) hypercalcemia?
- 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
What Physical exam or diagnostic imagining findings are seen in hyperparathyroidism?
- Often normal (no specific findings)
- Neck mass - usually small; usually not palpated
What tests exist for parathyroid evaluation?
- “Hypercalcemic panel”
- Ionized calcium
- PTH levels
- PTH-rp level ⇢ PTH related peptide produced by some cancers
- Vitamin D (Calcitriol) level
What are the possible interpretations of the “hypercalcemic panel”
- 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
What are the non-specific treatments for hypercalcemia?
- Saline diuresis - uses sodium chloride (0.9%)
- Furosemide - promotes Na loss,; give after rehydration
- Glucocorticoid - induces calcium excretion
What are specific treatments for hypercalcemia?
- 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
What is a Parathyroidectomy?
- 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
What are the physiological manifestations of Hypocalcemia?
- Tetany - may resemble seizure
- Cardiac changes - Diminished systolic function, cardiac dilation, myocardial irritability, bradycardia, prolonged S-T and Q-T segments
- CNS dysfuntion
What are the clinical signs of Hypocalcemia?
- Restlessness; neurological depression
- Seizures
- Muscle cramping (often rear legs)
- Muscle fasciculation / twitching
- Ataxia and stiff gait
- Facial and paw pruritis
- Aggression
- Panting
- Weakness
What does hypoparathyroidism look like on a parathyroid panel? compared to hypercalcemic disorders?
What is the emergency treatment for Hypocalcemia?
- 10% calcium gluconate - IV over 10-20 minutes
- Discontinue if bradycardia develops
- Avoid repeated IV boluses of calcium gluconate
What is the intermediate maintenance therapy for hypocalcemia?
- 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
What is the long-term maintenance therapy for hypocalcemia?
- Vit D2 (ergocalciferol)
- Calcitriol - Oral VIt D analogue; expense can be limitiing factor
- Oral calcium supplements - important early in treatment
