There are many treatment options for hyperthyroidism available and each has its with advantages and disadvantages.
Oral administration of antithyroid medication. Methimazole—TapazoleTM has long been the foundation of drug therapy for feline hyperthyroidism. It is exceedingly effective in correcting the condition, often inside of two to three weeks. Regrettably, about 10%-15% of cats will suffer side effects, such as vomiting, loss of appetite, lethargy, and sporadically blood cell abnormalities. Uncommon but more serious side effects include blood clotting disorders, severe facial itching with self-induced trauma, or liver problems. Most side effects are quite mild and in due course resolve, though some require discontinuation of the medication. Lifelong daily medication is necessary, which is a disadvantage to owners whose cats resist pilling. CBC and T4 levels need to be rechecked on a regular basis for the remainder of the cat’s life.
Hyperthyroidism is more often than not caused by a benign tumorcalled a thyroid adenoma that involves one or, more often, both thyroid glands. Fortunately, most hyperthyroid felines have benign, well-encapsulated tumors that are without difficulty removed. Surgery frequently results in a palliation and not a cure, but anesthesia can be challenging in these senior patients whose disease may have also affected their hearts and other organs. Although surgery may seem costly, in the long run, it usually ends up being less expensive than years and years of oral medication and regular blood work rechecks.
Radioactive iodine therapy is almost certainly the safest and most effective treatment alternative. Radioactive iodine, given by injection, turns out to be concentrated in the thyroid gland, where it irradiates and obliterates the hyperfunctioning tissue. No surgery or anesthesia is required, and only one treatment is typically needed to attain a cure.
Not so long ago, radioiodine treatment was performed in specialized, licensed facilities only, but many private treatment facilities are now found all through the country. Hospitalization may be long-drawn-out; depending on local or state ordinances, cats may need to be kept at the treatment facility for 10 to 14 days until the echelon of radioactivity in their urine and feces decreases to an acceptable level. Also, radioiodine therapy is expensive. The price tag has come down from about $1,200 to between $500 and $800 however.