QUESTIONS

1. What tests are available for hyperthyroidism & when do we use which?
    
2. Side effects from methimazole are usually evident in the first _____ months of therapy.
    
3. By what mechanism does methimazole (& PTU) employ to reduce thyroid level?
    
4. What mechanism does ipodate use?
    
5. What 4 side effects of methimizole (I usually spell it T-A-P-A-Z-O-L-E so pardon my changing spelling of the generic name) necessitate discontinuing the drug?
    
6. What percentage of cats have unilateral disease & what percentage have bilateral disease?
    
7. In surgerical therapy for hyperthyroidism, it is important to know which gland  to remove (or whether to remove both).  A pertechnitate scan will tell you but what if your gamma camera is in the shop?  You will have to use your eyes.  In what percentage of cats with bilateral thyroid disease does one of the diseased glands visually appear normal?
    
8. When you have to take out both glands you have a good chance of inducing hypoparathyroidism (which is usually transient).  If hypoPTHism is going to show up post-op, when does it usually make itself evident?
    
9. What type of subatomic particle does iodine 131 emit?
   
   
   
   
    

ANSWERS

1. T4 level - every elderly cat suspected of the disease should have one.
   
   Technitium scan - a must prior to radiotherapy however, I recall from school days, before these other tests were worked out, a scan was used on some questionable cases to see if they really were hyperthyroid or not.
   
   T3 suppression - for those with a normal T4 when you were just sure it was going to be high based on other findings.
   
   TRH stim (Mark Peterson's test).  Not having any TRH handy, personally, I like the T3 suppression test (T3 is easy to script out)
   
   TSH stim - hyperthyroid cats show a blunted response to TSH. Normal cats should stim to at least 2x basal level.  Hyperthyroid cats don't stim as high.
   
   
   
   
    
2. Tapazole side effects usually show in the first 3 months
   
   
   
   
    
3. Tapazole & PTU both block T4 synthesis in the thyroid gland.
   
   
   
   
    
4. Ipodate inhibits the converstion of T4 to T3 in the periphery.  It also may block the action of T3 at the cellular level.
   
   
   
   
    
5. The bad side effects are:  cholestasis, thrombocytopenia, agranulocytosis, and facial excoriations.
   
   
   
   
    
6. I've seen 2 different references.  One says 70% bilateral, 30% unilateral; the other says 80% bilateral, 20% unilateral.  You get the picture.
   
   
   
   
    
7. Abnormal thyroid gland looks normal in 15% of cases.  If you leave an abnormal one behind, the cat will be hyperthyroid again within the year.
   
   
   
   
    
8. Hypoparathyroidism occurs 1-4 days post-op usually.
   
   
   
   
    
9. Iodine 131 is an emitter of beta particles.  A beta particle is a high speed electron (remember, alpha particles-which are enormous as radioactive particles go- are helium nuclei, Beta particles are electrons - still big & gamma particles have no mass at all)  Beta particles, being relatively large, cannot penetrate beyond the thyroid tissue they are concentrated in.  This is why your patient doesn't get radiation damage elsewhere in the body.