Feline Hyper and Hypothyroidism Flashcards
what is the pathogenesis of feline hyperthyroidism?
excess production of T4 and T3 from adenomatous hyperplasia or benign adenomas
clinical findings associates with hyperthyroidism
- elevate liver enzymes (ALT +/- ALKP) due to increased metabolic demand and hypoxia to the liver
- decreased BUN/creatinine (due to increased GFR)
- unconcentrated urine, USG < 1.035
- Proteinuria
- erythrocytosis
what is the easiest diagnosis of hyperthyroidism in cats?
elevated thyroid hormone with clinical signs
90% will have elevated TT4
how would you explain a hyperthyroid cat with a normal T4?
early hyperthyroidism (80%) or nonthyroidal illness (20%)
__ of mild hyperthyroid cats have a normal T4
40%
T/F: Free T4 is a very sensitive test for HT4 and should be used as a sole diagnostic for hyperthyroidism
F, Free T4 is sensitive but should not be used as a sole diagnostic
the screening test of choice for hyperthyroidism is __
Total T4
Thyroid scintigraphy for hyperthyroidism
- dx confirmation
- adenoma vs carcinoma metastasis +/- metastasis
- unilateral v bilateral dz
- ID ectopic thyroid tissue
Tx Options for HT4 in cats
- methimazole
- surgical thyroidectomy
- radioiodine therapy
- iodine restricted diet
Methimazole pros v cons
transdermal or oral med that blocks thyroid perioxidase, preventing thyroid hormone production
Pro: cheap, easy
Cons: lots of side effects (vomiting, hepatotoxicity, IMHA, facial pruritis). Resistance may develop with long term use and cats get to a point where they cannot tolerate the high dose needed for treatment
Surgical Thyroidectomy pros v cons
Pros: can remove carcinomas and get histopath analysis
Cons: recurrence of HT4 possible, hypothyroidism can occur
Radioiodine Therapy pros v cons
SQ injection of radioactive iodine which emits beta particles that destroy abnormal thyroid tissue and spares normal tissue
Pros: curative
Cons: prolonged hospitalization with intense isolation and expensive
nutritional therapy pros v cons
special, iodine restricted diet that reduced thyroid hormone production (hills y/d)
Pros: easy, good options for cats intolerant of methimazole
Cons: not ideal for outdoor cats or multi cat households. may take a long time to work in severe cases
most cases of hypothyroidism in cats are what?
iatrogenic from tx of hyperthyroidism
why is it important to treat hypothyroid cats even if not symptomatic?
hypothyroidism decreases GFR, which can worsen kidney disease and decrease survival time, particularly in cats with pre-existing CKD
