The clinical importance of these studies seems to be that hyperthyroidism induces an artificial state of increased GFR, resulting
in a decrease in serum BUN and creatinine concentrations. Treating hyperthyroidism (whether with surgery, methimazole, or
radioiodine) reduces the GFR and causes an unmasking or progression of underlying chronic renal disease. Except for measuring
GFR before treatment, no reliable clinical sign or laboratory test helps practitioners predict which cat might exhibit a clinically
important deterioration in renal function after therapy. It is important to emphasize that the number of cats with severe
or clinically relevant declines in renal function posttreatment is small. However, based on these studies, it is prudent to
initiate low-dose methimazole therapy (or other forms of medical therapy) with renal and thyroid function monitoring after
seven to 10 days before performing surgery or radioiodine therapy.
The method chosen to treat a hyperthyroid cat depends on several factors, including cost, convenience, and the patient's current
health. Since hyper th y roidism can mask other illnesses such as renal disease, practitioners should conduct follow-up evaluations
with physical examinations and laboratory testing to monitor thyroid hormone concentrations and kidney function over time.
Cardiovascular parameters should also be examined periodically, especially if hypertension or heart enlargement were noted
at the time of diagnosis. The frequency of checkups will depend on the treatment method chosen and the patient's response
David S. Bruyette, DVM, DACVIM
VCA West Los Angeles Animal Hospital
1818 S. Sepulveda Blvd.
West Los Angeles, CA 90025
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