HypERthyroidism Flashcards
Hyperthyroidism
an endocrine Dz characterized by excessive circulating amounts of thyroid hormone
Location of thyroid glands
mid-cervical region adjacent to the trachea
What is the thyroid gland made up of?
follicles
What is inside of the thyroid follicles?
colloid
What is colloid made of?
thyroglobulin
What is thyroglobulin?l
a large protein that contains each of the thyroid hormones
Tyrosine molecules + ______________ = thyroid hormone
iodine
What secretes colloid?
Epithelial cells that line the follicles
What are thyroid hormones cleaved from? When are they cleaved?
cleaved from thyroglobulin prior to release of the hormone into circulatory system
What pathological process in the thyroid gland leads to hyperthyroidism?
an overgrowth of thyroid tissue either due to benign or malignant tumor; in either case, the additional tissue is functional
What species is most at risk for hyperthyroid?
cats
Common clinical signs of hyperthyroid Dz
Increased cardiovascular func (HR, BP) Hyperactivity Muscle wasting Vomiting Occasionally diarrhea polyphagia
What does increased perfusion to the kidneys result in? What about increased BP?
- increased perfusion to kidneys results in polyuria with compensatory polydipsia
- increased BP can lead to retinal hemorrhage or detachment resulting in blindness
Why is hyperactivity seen in hyperthyroid cats?
secondary due to increased metabolism
Why are muscle wasting and weight loss seen with hyperthyroid cats?
increased muscle activity and increased energy expenditure
What causes vomiting in hyperthyroid cats?
increased metabolism of liver and GI tract
Why are hyperthyroid cats polyphagic?
body is constantly burning energy and looking for more energy
Abnormalities on PE with hyperthyroidism
- poor body condition due to muscle wasting and weight loss
- haircoat greasy and unkempt
- increased size of thyroid gland
Abnormalities on bloodwork with hyperthyroidism
- Polycythemia (increased metabolism –> increased demand at tissue lvl for O2 –> RBC production amps up)
- Elevated liver enzymes (due to increased metabolic demand on liver)
- Azotemia
- Elevated T4
What hormonal test is most beneficial in hyperthyroid confirmation?
Serum T4 concentration test
4 Specialized tests that may be beneficial for hyperthyroidism confirmation
T3 suppression test
TSH rsponse test
TRH stimulation test
Radionuclid scan of thyroid gland
3 Ways to treat hyperthyroidism
Methimazole
Thyroidectomy
Radioactive Iodine
Methimazole
- type of Tx
- what it does
- pros
- cons
- tablet, orally SID
- reduces serum thyroid hormone concentration by blocking synthesis of thyroid hormones by thyroid gland; does not destroy thyroid tissue, so it is not a permanent cure
- Pro: easy to adjust dose and to give, inexpensive, no anesthesia/hospital stay/special equipment
- Con: vomiting, anorexia, development of bone marrow disorder
Thyroidectomy
- type of Tx
- what it does
- pros
- cons
- surgery
- removes one or both glands; curative if not ectopic tissue
- Pro: can cure Dz
- Con: requires anesthesia which often isn’t ideal for older patients with increased metabolism of organs, expensive, hypocalcemia may result
Radioactive Iodine
- what it does
- pros
- cons
- overactive thyroid tissue takes up cytotoxic radioactive iodine thus destroying abnormal thyroid cells (unilateral or bilateral) and any ectopic tissue that might be present
- Pro: potential to cure with 1 dose, no anesthesia, reactions are rare
- Con: may require multiple doses, expensive, limited availability, prolonged hospital stay
2 Complications seen with untreated hyperthyroidism
Heart
-increased HR and increased pressure in circulatory system increases workload on the heart which leads to thickening of cardiac muscle (usually LV) resulting in secondary hypertrophic cardiomyopathy and heart failure
Eyes
-increased pressure in ocular circulation may lead to retinal hemorrhage and detachment resulting in sudden blindness
Potential complication that may occur when starting therapy for hyperthyroidism
unmasking kidney failure
- hyperthyroidisms can help sustain failing kidneys because it increases BP, and increased BP results in increased blood flow (perfusion) to kidneys
- therapy normalizes BP, so blood flow to kidneys decreases and may reveal kidney failure
How to treat if CRF and hyperthyroid?
balance methimazole to a level that drops thyroid hormone enough that it lessens risks of hyperthyroidism but also still allows for some increased BP for increased perfusion to kidneys
