Management of Hyperthyroidism Flashcards
T/F: hyperthyroidism is uncommon in cats
F, its the most common endocrinopathy of cats effecting about 10% of cats >10 years of age
hyperthyroidism is excess production of __ and __ caused by __ or __
hyperthyroidism is excess production of T3 and T4 caused by thyroid adenoma or adenomatous hyperplasia
what percent of cats with hyperthyroidism will have an elevated T4?
90%, and most will have a thyroid slip
What are the goals of therapy for hyperthyroidism?
euthyroidism which is 1.5 to 3.0 ug/dL and to avoid hyperthyroidism or hypothyroidism or worsening kidney function
why would CKD manifest after treatment of hyperthyroidism?
CKD and hyperthyroidism may both be present but the CKD won’t show up on bloodwork because the hyperthyroidism decreases muscle mass making the CK value lower. Once you treat the hyperthyroidism 25% will have azotemia and the CKD should be treated
what are the 2 management methods for hyperthyroidism?
Methimazole and Iodine restricted diets
what 2 methods of management for hyperthyroidism are curative?
Surgical thyroidectomy and radioiodine therapy
likely to recur even with these procedures
Methimazole is usually given __ with the fastest response achieved by 4 weeks when given __. It can be used __ term but tumors still progress and __ is common resulting in increased doses
Methimazole is usually given orally with the fastest response achieved by 4 weeks when given BID. It can be used long term but tumors still progress and resistance is common resulting in increased doses
Tumors during treatment with methimazole may transform into __
carcinomas that don’t respond to the medication
if a cat had concurrent CKD when you start treatment for hyperthyroidism with methimazole, what should you consider?
when the hyperthyroidism is treated then there will be increased renal blood flow and creatinine levels will rise. So to avoid further nephrotoxicity with CKD patients start at a low dose and titrate to effect
when should you do a recheck after initial methimazole treatment?
2-4 weeks with a cbc/chem T4, BUN, creatine, USG and BP
cats may experience side effects of GI signs, blood dyscrasis, hepatotoxicity, facial pruritis
t/f: cats that develop azotemia with hyperthyroidism have a shorter survival time
T
what percent of cats with hyperthyroidism develop azotemia and how can you preview it?
25%, treat with methimazole and CKD will manifest
what is considered the treatment of choice for hyperthyroidism?
Radioiodine, it destroys the abnormal thyroid tissue and has 95% efficacy with one treatment
what is a risk of radioiodine treatment of hyperthyroidism?
causing iatrogenic hypothyroidism
Nutritional therapy for hyperthyroidism
Hills y/d will have improved clinical signs within 4 weeks. However, theres no improvement with BW, tachycardia or GFR and liver values may not improve
who would be a good candidate for nutritional therapy of hyperthyroidism?
cats who dont tolerate methimazole
concurrent disease that preclude 1131
cats with concurrent early renal insufficiency
surgical thyroidectomy are __ common and risk __thyroidism, hyoparathyroidism and recurrence
surgical thyroidectomy are less common and risk hypothyroidism, hyoparathyroidism and recurrence
what is the most common type of hypothyroidism in cats?
iatrogenic most commonly from radioiodine therapy and may be transient resolving in 3-6 months or permanent in 10%
why do we care if they accidentally become hypothyroid from radioiodine?
It hurts the kidneys! they’re more likely to become azotemic decreasing GFR and survival
what are clinical signs of hypothyroidism in a cat?
weight gain
decreased appetite
lethargy
pu/pd
+/- dermatologic changes
overlap with resolution of hyperthyroidism
inapparent at time of diagnosis
describe the two types of hypothyroidism
overt = increased TSH and decreased T4
subclinical = normal T4, increased TSH
how often should you monitor a hypothyroid cat after treatment?
1 month
3 months
6 months
+/- 12 months
T4, TSH, Chem or renal panel, UA
if the hypothyroidism is caused by I131 then treat at month 3 and at 6 months its likely permanent
when should you start treating hypothyroidism even if its subclinical
if theres new or worsening azotemia
what is the treatment for hypothyroidism? what are its benefits?
levothyroxine
improved kidney function and increased survival
how can you prevent hypothyroidism in cats?
lower doses of I131 in mild to moderate cases of hyperthyroidism
