Endocrine3- Hyperthyroidism

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Endocrine3- Hyperthyroidism
2015-11-26 11:46:27
vetmed endocrine3

vetmed endocrine3
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  1. Most common endocrine disease of cats.
  2. In >97% of cases, hyperthyroidism is caused by... 92)
    thyroid adenoma or adenomatous hyperplasia (VERY RARELY adenocarcinoma).
  3. In what animals do you usually see hyperthyroidism?
    any breed, any sex, older cats ~13 years
  4. Clinical signs of hyperthyroidism. (6)
    weight loss, polyphagia, PU/PD, restlessness, vomiting, heat intolerance
  5. What are PE findings with a hyperthyroid cat? (9)
    palpable thyroid glands (lentil to lime bean-sized), thyroid slip, thin, tachycardia/systolic murmur, hyperactive, +/- poor hair coat, +/- hyperthermia, +/- small kidneys, +/- hypertension
  6. What CBC abnormalities often accompany hyperthyroidism? (2)
    increased PCV (thyroid stimulates BM), macrocytosis
  7. Biochem abnormalities that often accompany hyperthyroidism. (3)
    increased liver enzymes (ALT, AST, ALP), azotemia, mild hyperphosphatemia
  8. UA findings with hyperthyroidism. (1)
    USG > 1.035 (isosthenuria in a hyperthyroid cat is very concerning--> evaluate renal function for concurrent CKD)
  9. How do you definitively diagnose hyperthyroidism?
    total T4 measurement > 5μg/dL
  10. What may cause normal T4 in hyperthyroid cats (in less than 10% of cases)? (2)
    daily fluctuations early in disease, euthyroid-sick syndrome (non-thyroidal illness causing a lower thyroid hormone-- commonly CKD in old cats!!)
  11. Can you measure total T3 to diagnose hyperthyroidism?
    no, not reliable indicator... normal in many hyperthyroid cats
  12. Is TSH used to screen for hyperthyroidism?
    some believe undetectable TSH cats are at higher risk for hyperthyroidism..... not really used
  13. What is the principal of the T3 suppression test (not done as much anymore)?
    giving T3 to normal cats suppresses TSH release, lower the T4; in a hyperthyroid cat, the T4 does not decrease
  14. What might you see on radiograph of a hyperthyroid cat?
  15. What ECG findings may be present with hyperthyroidism? (2)
    tachycardia, increase R wave
  16. What is the major advantages on nuclear scintigraphy?
    can identify ectopic disease (thyroid adenocarcinoma of ectopic thyroid tissue)
  17. What are the 4 forms of treatment for hyperthyroidism?
    drugs- methimazole, thyroidectomy, radiotherapy, nutrition- Y/d Hill's Rx diet
  18. Describe the action of Methimazole?
    inhibits thyroid peroxidase (thus blocks iodide incorporation into thyroglobulin)
  19. Will the thyroid nodule get smaller with txt with methimazole?
  20. What is post-txt care with methimazole?
    check tT4 after 4 weeks of txt, if drug is stopped, all effects are reversible; CBC/chem should be monitored for side effects (usually occur in first 1-2months of txt)
  21. What is the usually effective dose of methimazole?
    2.5-5mg BID
  22. What side effects can occur with methimazole? (8)
    anorexia, vomiting, lethargy, [rarely] cutaneous excoriations, hematologic changes, increased liver enzyme, IMHA, platelet dysfunction
  23. What happens if you discontinue use of methimazole?
    cat reverts to hyperthyroid state 24-48hrs after discontinuation
  24. What is another way to use methimazole other than PO?
    transdermally in inner-pinna SID (5mg) [WEAR  GLOVES]
  25. What are the advantages of surgery to treat hyperthyroidism? (2)
    potentially curative, available in private practice
  26. What are the disadvantages of surgery to treat hyperthyroidism? (6)
    irreversible, damage to parathyroid blood supply, anesthetic risk, risk of Horner's syndrome, development of disease in contralateral lobe, clinical hypothyroidism (rare)
  27. How does treatment of hyperthyroidism with radioactive iodine work?
    functioning cells that take up iodine are killed by beta-particles from radioactive iodine (healthy thyroid tissue is suppressed and therefore, not affected)
  28. What is the ideal treatment for hyperthyroidism, and what is the caveat to it?
    radioactive iodine; expense and expertise
  29. When do you see results after radioactive iodine treatment?
    serum T4 decreases to normal over days to weeks- 95% are euthyroid within 3 months after one treatment
  30. What special precautions must be followed by owners after radioactive iodine therapy? (6)
    [30 days] flushable litter and flush soiled litter down toilet, wash hands after handling cat/cat stuff, cat must be confined to house, no exposure to children or pregnant, cat must wear radioactive ID collar, blood/urine samples handled appropriately
  31. What nutritional changes can be made to manage hyperthyroidism in cats?
    iodine-restricted diet (Hill's y/d) exclusively for 3 months--> decreased T4
  32. What are some issues with the Hill's y/d diet? (5)
    T4 not low enough, cats must eat ONLY y/d which can be difficult, long-term effects unknown, low protein/high carb (too low protein?), palatability
  33. What are potential complications of feline hyperthyroidism? (3)
    increased RBF and GFR--> decreased BUN and Cre, making the kidneys look better than they are; CKD can lower T4 and mask hyperthyroidism; hypertension may not resolve with txt (require Ca2+ channel blocker)
  34. Hyperthyroidism can mask __________, and vice versa.
  35. If you have a cat that you are suspecting hyperthyroidism and kidney disease, how should you treat?
    Methimazole challenge test (because you can take it back)
  36. How can you determine if the kidneys are functional enough to go ahead with I131 treatment of hyperthyroidism?
    Methimazole challenge- if therapeutic dose of methimazole is achieved with an increase in BUN and Cre, and remain stable for 30 days
  37. What is the prognosis of hyperthyroidism?
    very good- average survival is 2 years (remember these cats are already old!)... often die of something else