Thyroid function in 36 dogs with leishmaniosis due to Leishmania infantum before and during treatment with allopurinol with or without meglumine antimonate

Hypothyroidism may predispose to the development of canine leishmaniosis or it may appear during the course of the latter due to infiltration and destruction of the thyroid gland by infected macrophages. The main purpose of this study was to evaluate thyroid function through measurement of serum total thyroxin (tT4), free thyroxin (fT4), and canine thyroid stimulating hormone (cTSH) concentrations in 36 dogs with leishmaniosis, before and after 2 and 4 weeks of treatment with allopurinol with or without meglumine antimonate. Before treatment 27/36 (75%) dogs had serum tT4 concentrations below the lower limit of the reference interval but only 2 of them had concurrently serum fT4 concentrations below the lower limit of the reference interval and none had increased serum cTSH concentrations. During treatment there were no significant changes in serum tT4 or fT4 concentrations, whereas a significant increase in serum cTSH was observed. Two dogs had decreased serum tT4 and fT4 but normal cTSH concentrations before treatment and two other dogs had decreased serum tT4 and increased cTSH, but normal fT4 concentrations during the treatment period. Although hypothyroidism could not be definitively excluded in these dogs it is considered unlikely based on their overall hormonal profile, clinical presentation, and response to treatment. Therefore, hypothyroidism does not appear to be an important predisposing disease or a frequent complication of canine leishmaniosis.