QUANTITATIVE THYROID SCINTIGRAPHY IN GREYHOUNDS SUSPECTED OF PRIMARY HYPOTHYROIDISM

Abstract

The existence of hypothyroidism in greyhounds remains controversial and its investigation is complicated by the low circulating thyroid hormone concentrations typically found in healthy dogs of this breed. Quantitative measurement of thyroidal technetium-99m pertechnetate ((99m)TcO4-) uptake is known to be useful in assessing thyroid function in other breeds. The aim of this study was to evaluate thyroid scintigraphy as a method of assessing thyroid function in greyhounds suspected of primary hypothyroidism. Twenty greyhounds (eight females, 12 males) were studied. Thirteen had bald thigh syndrome and seven poor performance and low total T4. Total T4 concentrations were decreased in 18 (90%), and free T4 in two (10%) dogs. All canine thyroid stimulating hormone concentrations were within the reference interval. Thyroidal (99m)TcO4- uptake values (mean +/- SD, 0.76 +/- 0.26%) were within the reference limits published for euthyroid dogs (0.39-1.86%) making hypothyroidism highly unlikely. There were no significant differences (P < 0.05) when comparing data between dogs with bald thigh syndrome (13 dogs) and the remaining dogs (seven dogs). Seventeen (85%) dogs had higher uptake in the left thyroid gland than in the right that might reflect an anatomic feature of the greyhound breed. Calculation of percent thyroidal uptake of (99m)TcO4- is more accurate than thyroid: salivary gland ratios because of high variability in salivary gland uptake. Percent thyroidal uptake of (99m)TcO4- should be used when assessing thyroid function scintigraphically in the greyhound breed.