SACCM 78: Thyroid Storm Flashcards
What are the causes of thyrotoxicosis versus hyperthyroidism?
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
How do causes of thyrotoxicosis differ between cats and dogs?
- 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
What is D1 and D2 and why does their function matter for the treatment of thyrotoxicosis?
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)
List causes for increased cellular response to thyroid hormones in cases of thyroid storm
- sepsis, infection
- hypovolemia
- hypoxemia
- ketoacidosis
- lactic acidosis
List 11 precipitating events for feline thyroid storm
- 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
How is thyroid storm diagnosed in people?
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
How is thyroid storm diagnosed in cats?
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
List 7 cadiovascular signs in cats with thyroid storm
- arrhythmias - atrial fibrillation, ventricular arrhythmias
- gallop rhythm
- sinus tachycardia
- CHF - pleural effusion, pulmonary edema
- cardiomegaly
- hypertension
- thromboembolic disease
Explain the pathophysiology of ventroflexion in cats with thyroid storm
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
List 4 neuromuscular signs in feline thyroid storm
- seizures
- behavioral changes
- obtundation/mental dullness
- muscle weakness/cervical ventroflexion
Why do cats with thyroid storm develop ocular lesions? List the ocular lesions
from severe hypertension
hyphema, retinal lesions and detachment
What CBC/cytology changes are typically seen in hyperthyroid cats?
erythrocytosis, macrocytosis, Heinz body formation
mature neutrophilia, lymphopenia, eosinopenia (stress leukogram)
What biochemical abnormalities are typical for hyperthyroid cats?
- hypokelamia
- hyperglycemia
- elevated liver enzymes
- hyperbilirubinemia
if pleural effusion/heart failure - low Na/K ratio possible
What are the three medications used to reduce the production or secretion of thyroid hormone?
- Methimazole
- stable iodine compounds, e.g., potassium iodine
- corticosteroids
What is the mechanism of action by which methimazole helps in thyroid storm?
Methimazole inhibits iodine incorporation into tyrosine residues by interfering with the oxidation process –> i.e., prevents the synthetis of ative thyroid hormone
What is the normal dose for methimazole and how do you adjust it in suspected renal insufficiency?
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
What is mechanism of action by which potassium iodine helps with thyroids storm?
- prevents release of already formed thyroid hormones
- stable iodine compound
- at large doses –> will also reduce the synthesis of thyroid hormones
What is the recommended dose of potassium iodine and how should it be administered?
25 mg PO q8h
give an hour after methimazole administration - large load of iodine will initially stimulate thyroid hormone production (“iodine-induced thyrotoxicosis”)
Why are corticosteroids indicated for the treatment of thyroid storm?
- 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
Discuss dosages and specific benefits/disadvantages of 3 options of beta-blockers for cats with thyroid storm
- 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
- Atenolol - better bioavailability, does not affect T4 conversion, 1 mg/kg PO q12-24h
- 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
