Research Communications of the 24th ECVIM-CA Congress

No conflicts of interest reported. Iatrogenic hypothyroidism is a recognized complication of radioiodine treatment for hyperthyroidism in cats. At our clinic where we use a variable 131-I dosing protocol (based on tumor volume and severity of hyperthyroidism), the prevalence of overt or subclinical hypothyroidism is at least 7%. During the 15-month period from October 2012 to March 2014, we treated 19 cats with iatrogenic hypothyroidism, which had developed 41-323 days (median, 119 days) after treatment with radioiodine (median dose, 100 Mbq). These cats ranged in age from 9-19 years (median, 14 years); all were DSH/DLH; 14 (74%) were female and 5 were males. New or worsening azotemia (>140 lmol/L) was documented in 16 (84%) and 2 (10.5%) cats, respectively. Diagnosis of hypothyroidism was based on the following: 1) low to low-normal serum concentrations of T4, FT4, and T3; 2) high serum TSH concentration (>0.5 ng/dl); and 3) less-than-normal amounts of residual tissue on thyroid scintigraphy. All cats were given thyroid hormone replacement as a liquid L-T4 preparation (Leventa; Merck Animal Health). Cats were monitored at 1-3 month intervals by repeating serum T4 and TSH concentrations 3-4 hours after the morning L-T4 dose.