Tier 1 — must know
Feline
Endocrine
Hyperthyroidism
Thyrotoxicosis in older cats · weight loss with polyphagia · cardiac consequences
⏱ 3–4 min read · Topic 1 of 5
5
Practice Qs
4
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High
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Exam core — read this first
Classic triad → weight loss + polyphagia + hyperactivity in cat > 10 years
Cardiac consequences → tachycardia, gallop rhythm, murmur, hypertrophic cardiomyopathy
Diagnosis → elevated T4; free T4 by ED if T4 is borderline (GDV, illness)
Board logic → treat hyperthyroidism first; CKD may unmask after euthyroid state restored
Key data
T4
↑ Elevated
Screening test
Free T4 (ED)
↑ Confirm if borderline
Less affected by illness
BUN/Cr
Check before treatment
CKD may unmask
Blood pressure
↑ Common
Hypertension screening
Practice questions
A 13-year-old cat has lost 1.5 kg over 3 months despite a ravenous appetite. PE reveals palpable thyroid nodule and tachycardia. Most likely diagnosis?
What is the first-line oral medication for feline hyperthyroidism?
What is the curative treatment of choice for feline hyperthyroidism?
A hyperthyroid cat has normal BUN/Cr. After starting methimazole, the cat becomes azotemic. Most likely explanation?
A hyperthyroid cat has gallop rhythm and systolic murmur. Echo shows LVH without outflow obstruction. Likely mechanism?