Chapter 70 - hypothyroid crisis in the dog

Question 1

why is myxoedema coma a misnomer?

Answer 1

many patients in hypothyroid crisis are not comatose and do not have myxoedema

Question 2

which breed is at increased risk of hypothyroid crisis?

Answer 2

Rottweilers

Question 3

in a dog with hypothyroid crisis, how soon after administration of levothyroxine is improvement in mentation and ambulation expected?

Answer 3

24-30h

Question 4

pathophysiology of altered mental state in hypothyroid crisis

Answer 4

decreased blood flow and oxygen delivery
hyponatremia
lack of direct effect of thyroid hormone
disruption of integrity of BBB

Question 5

pathophysiology of hypothermia in hypothyroid crisis

Answer 5

hypothalamic dysfunction
decreased calorigenic effect
hypoperfusion & hypotension

Question 6

why may dogs in hypothyroid crisis appear normothermic?

Answer 6

effect of hypothermia + pyrexia if concurrent infectious/inflammatory disease

Question 7

pathophysiology of hypothyroid cardiomyopathy

Answer 7

decreased number of b-adrenergic receptors
decreased b-receptor affinity for catecholamines
–> decreased isotropy, chronotropy
increase in a-myosin heavy chains (decreased ATPase activity)
decrease in b-myosin heavy chains (increased ATPase activity)

Question 8

typical clinical picture with hypothyroid cardiomyopathy

Answer 8

impaired left ventricular function or atrial fibrillation

Question 9

clinical picture of cardiovascular dysfunction during hypothyroid crisis

Answer 9

bradycardia, decreased contractility, cardiac enlargement, hypotension (diastolic hypertension has also been documented)