SACCM 78: Thyroid Storm Flashcards

1
Q

What are the causes of thyrotoxicosis versus hyperthyroidism?

A

thyrotoxicosis can be from any of the following:
* excessive production and secretion from an overactive thyroid gland (i.e., from hyperthyroidism)
* leakage from a damaged thyroid gland
* exogenous source

hyperthyroidism describes solely thyroid gland hyperfunction

i.e., thyrotoxicosis can occur in the absence of hyperthyrodism, but rare

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2
Q

How do causes of thyrotoxicosis differ between cats and dogs?

A
  • cats usually have thyrotoxicosis from hyperthyroidism
  • dogs less common, but can be from functional thyroid carcinoma, oversupplementation of thyroid replacement hormone (in hypothyroid dogs), or consuming uncooked organ meat
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3
Q

What is D1 and D2 and why does their function matter for the treatment of thyrotoxicosis?

A

Deiodinase D1 is the main enzyme converting T4 to T3 in the hyperthyroid animal
Deiodinase D2 is the main enzyme for conversion in the euthyroid animal

D1 enzyme may be a target of the sympathetic nervous system –> could be inhibited by beta-adrenergic receptor antagonists (i.e., beta-blockers)

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4
Q

List causes for increased cellular response to thyroid hormones in cases of thyroid storm

A
  • sepsis, infection
  • hypovolemia
  • hypoxemia
  • ketoacidosis
  • lactic acidosis
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5
Q

List 11 precipitating events for feline thyroid storm

A
  • Radioactive iodine therapy
  • Thyroid or parathyroid surgery
  • Abrupt withdrawal of antithyroid medications
  • Thyroidal surgery, parathyroidal surgery, or nonthyroidal surgery
  • Vigorous thyroid palpation
  • Stress
  • Administration of iodinated contrast dyes
  • Administration of stable iodine compounds
  • Infection
  • Amiodarone therapy
  • Nonthyroidal illness
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6
Q

How is thyroid storm diagnosed in people?

A

Based on a point system based on the presence of clinical signs + the presence of a precipitating event

Clinical signs categories:
1. Fever
2. CNS signs
3. GI and liver signs
4. cardiovascular signs

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7
Q

How is thyroid storm diagnosed in cats?

A

Based on the identification of thyrotoxicosis, clinical signs, and presence of precipitasting events

Thyrotoxicosis is demonstrated by elevated total T4 or a high-normal total T4 + elevated free T4

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8
Q

List 7 cadiovascular signs in cats with thyroid storm

A
  • arrhythmias - atrial fibrillation, ventricular arrhythmias
  • gallop rhythm
  • sinus tachycardia
  • CHF - pleural effusion, pulmonary edema
  • cardiomegaly
  • hypertension
  • thromboembolic disease
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9
Q

Explain the pathophysiology of ventroflexion in cats with thyroid storm

A

increased catecholamine activity and thyroid hormone levels leads to hypokalemia from increased NaKATPase pump activity - leading to muscle weakness and ventroflexion

thyroid hormones upregulate NaKATPase pumps directly

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10
Q

List 4 neuromuscular signs in feline thyroid storm

A
  • seizures
  • behavioral changes
  • obtundation/mental dullness
  • muscle weakness/cervical ventroflexion
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11
Q

Why do cats with thyroid storm develop ocular lesions? List the ocular lesions

A

from severe hypertension
hyphema, retinal lesions and detachment

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12
Q

What CBC/cytology changes are typically seen in hyperthyroid cats?

A

erythrocytosis, macrocytosis, Heinz body formation
mature neutrophilia, lymphopenia, eosinopenia (stress leukogram)

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13
Q

What biochemical abnormalities are typical for hyperthyroid cats?

A
  • hypokelamia
  • hyperglycemia
  • elevated liver enzymes
  • hyperbilirubinemia

if pleural effusion/heart failure - low Na/K ratio possible

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14
Q

What are the three medications used to reduce the production or secretion of thyroid hormone?

A
  • Methimazole
  • stable iodine compounds, e.g., potassium iodine
  • corticosteroids
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15
Q

What is the mechanism of action by which methimazole helps in thyroid storm?

A

Methimazole inhibits iodine incorporation into tyrosine residues by interfering with the oxidation process –> i.e., prevents the synthetis of ative thyroid hormone

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16
Q

What is the normal dose for methimazole and how do you adjust it in suspected renal insufficiency?

A

5 mg/cat PO q12h - can also be given rectally or transdermally
- reduce dose by half if renal insuffiency is suspected to prevent rapid decrease in renal blood flow

17
Q

What is mechanism of action by which potassium iodine helps with thyroids storm?

A
  • prevents release of already formed thyroid hormones
  • stable iodine compound
  • at large doses –> will also reduce the synthesis of thyroid hormones
18
Q

What is the recommended dose of potassium iodine and how should it be administered?

A

25 mg PO q8h
give an hour after methimazole administration - large load of iodine will initially stimulate thyroid hormone production (“iodine-induced thyrotoxicosis”)

19
Q

Why are corticosteroids indicated for the treatment of thyroid storm?

A
  • hypothalaminc-pituitary-adrenal axis impaired in patients with thyrotoxicosis –> can lead to decreased adrenal reserves –> may need supplementation
  • corticosteroids may reduce release of thyroid hormone from thyroid gland
  • corticosteroids may block the conversion of T4 to T3 in peripheral tissues
20
Q

Discuss dosages and specific benefits/disadvantages of 3 options of beta-blockers for cats with thyroid storm

A
  1. Propranolol - also inhibits peripheral conversion of T4 to T3, poor oral bioavailability and short half-life in cats, 5mg PO q8h or 0.02 mg/kg IV over 5 minutes
  2. Atenolol - better bioavailability, does not affect T4 conversion, 1 mg/kg PO q12-24h
  3. Esmolol - fast but short acting, does not affect T4 conversion, IV CRI - loading dose 0.1-0.5 mg/kg over 1 minute then 10-200 mcg/kg/min