A PROSPECTIVE-STUDY OF 66 CASES OF FELINE HYPERTHYROIDISM TREATED WITH A FIXED-DOSE OF INTRAVENOUS I-131

Sixty-six cats with hyperthyroidism were treated with a fixed intraven ous dose of 150 mBq of radio-iodine (I-131). Sixty-two cats (93%) were treated successfully. One cat's serum thyroxine (T4) level remained e levated after therapy. Two cats regressed to hyperthyroidism 13 and 19 months after I-131. One cat died immediately after I-131 injection. T wo cats, with subnormal T4 values (< 15nmol/l) after therapy, showed s igns of hypothyroidism: lethargy, obesity and hair loss. Forty-four of the 66 cats were still alive and euthyroid. Eighteen cats have died o f causes unrelated to hyperthyroidism. One cat was euthanased due to r ecurrence of hyperthyroidism, and one for a degenerative myelopathy. O ne cat died from progression of hyperthyroid-related cardiac disease. The present study documents the successful use of a fixed dose of I-13 1 in Australia, comparable to overseas studies using fixed doses or do ses which have been based on a combination of thyroid gland weight and /or radiotracer studies or basal thyroxine concentrations.