Study of factors that influence the outcome of 131I treatment in hyperthyroidism secondary to nodular goitre

Abstract Objective To assess the outcome after 131 I treatment in patients with multinodular (MNG) and nodular toxic goitre (NTG) according to the administered dose (555 or 740 MBq) and other factors related to the patient, pathology, or previous treatments. Material and methods A retrospective study was conducted on 108 patients (67 MNG and 41 NTG) treated in our department, with a follow-up period of at least 2 years. Development of hypothyroidism and treatment failure were evaluated along with their relationship with the administered dose and other factors such as age, sex, grade of hyperthyroidism, type of goitre, presence of autoimmunity, or previous antithyroid medication. Results More than one-third (36.9%) of MNG patients, and even higher proportion of NTG patients (51.2%) developed non-transient hypothyroidism, particularly in those receiving 740 MBq (66.7%). No relationship was found with any other variable. The development of early hypothyroidism (before one year) was also not related to any variable. Treatment failure was not related to the dose, but in MNG there was a relationship with male gender, presence of autoimmunity, or previous antithyroid drugs use. Conclusions The high rate of hypothyroidism obtained with high doses of 131 I in hyperthyroidism secondary to nodular goitre treatment suggests that lower doses might be sufficient to control the disease without an increase in treatment failures. Only patients with positive autoimmunity, in previous anti-thyroid medication, and perhaps male gender in MNG might be given higher doses, as the failure rate increases, but further studies are required.