SACCM 79: Hypothyroid Crisis in the Dog Flashcards
What is the proposed cause for altered mental status in hypothyroid crisis?
- decreased direct effect of thyroid hormones on the brain
- hypotension –> decreased blood flow and DO2 to the brain
- disrupted BBB
- hyponatremia
What is the suspected cause for hypothermia in hypothyroid crisis?
- dysfunctional hypothalamus from lack of thyroid hormones
- decreased calorigenic effect of thyroid hormones
- hypotension/hypoperfusion
Calorigenic effect = heat production
What are the proposed causes of hypothyroid cardiomyopathy?
- thyroid hormones increase the number of beta-adrenergic receptors and their affinity to catecholamines –> needed for inotropicd and chronotropic effects –> contractility and HR
- hypothyroidism –> increase in alpha-myosin heavy chains (MHC) –> decreased ATPase activity
- decrease in beta-MHC (more ATPase activity)
–> impaired left ventricular function
–> atrial fibrillation
–> bradycardia, decreased contractility, cardiac enlargement, hypotension, possibly diastolic hypotension
What causes diastolic hypertension in hypothyroid crisis?
- peripheral vasoconstriction and central shunting from hypothermia and low VO2
What are the proposed causes for myxedema in hypothyroid crisis?
- hyaluronic acid accumulation in the dermis
- impaired renal perfusion and inability to excrete water
- excessive ADH secretion
List the 3 reported causes for predisposing to hypothyroid crisis in dogs
- infection
- glucocorticoid administration
- surgery
How could NSAIDs in theory contribute to the development of hypothyroid crisis?
NSAIDs may cause suppression of TSH secretion
List clinical signs of untreated hypothyroidism
- obesity/weight gain
- lethargy/mental dullness
- weakness
- dermatologic abnormalities - hyperkeratosis, alopecia, thin hair coat
What are the classic physical hallmarks or hypothyroid crisis, and how consistent are these?
- myxedema
- bradycardia
- hypoventilation
- hypothermia
- hypotension
- coma
very inconsistent and dogs usually don’t have all these signs - case series of 7 dogs with hypothyroid crisis showed very variable CS (Pullen and Hess, JVIM, 2006)
What are typical clinicopathologic abnormalities in dogs with hypothyroid crisis?
- nonregenerative anemia
- hypercholesterolemia
- lipemia
- increased ALKP
- hyponatremia and hypoglycemia noted anecdotally in dogs
What is the proposed cause of nonregenerative anemia in hypothyroidism?
- thyroid hormones bind to thyroid hormone receptors on erythroid progenitors –> increases erythroid proliferation
- thyroid hormones increase the expression erythropoietin gene
List all possible explanations for hyponatremia in hypothyroid crisis
- increased ADH
- decreased renal Na reabsorption
- impaired water clearance
- decreased atrial natriuretic peptide
- low plasma renin activity
- low aldosterone cc
How and why do glucose levels in dogs and people with hypothyroid crisis differ?
People - hypoglycemia - decreased insulin clearance
dogs - experimentally hyperglycemia - decreased insulin sensitivity
List drugs that can lower thyroid hormone levels
- glucocorticoids
- nonsteroidal anti-inflammatory drugs
- anticonvulsants
- antituberculosis drugs
- propranolol
- lithium
List differentials for hypercholesterolemia
- hypothyroidism
- DM
- Cushing’s
- PLN
- cholestatic disease
- postprandial hyperlipidemia
- primary hyperlipidemia (Miniature Schnauzers, Shetland Sheepdogs)
- lipoprotein lipase deficiency
- idiopathic causes
- iatrogenic causes (e.g., steroid administration)
