Impact of extrathyroidal autoimmune diseases on clinical features and the efficacy of Iodine‐131 therapy in patients with differentiated thyroid cancer

Abstract Objective The aim of this study is to assess the impact of extrathyroidal autoimmune diseases (ADs) on the clinical characteristics and efficacy of iodine‐131 ( 131 I) therapy in patients with differentiated thyroid cancer (DTC). Methods Patients with DTC who were received 131 I therapy simultaneously were classified into the combination group ( n = 35) and noncombination group ( n = 146) depending on the presence of ADs. The clinical characteristics, such as gender, age, tumor lesions, lymph node metastasis, distant metastasis, 131 I therapy efficacy, and use of levothyroxine, were compared between the two groups. Statistical analysis was conducted using SPSS 26.0 and R 4.0.3. Results There was a statistically significant difference in age between the combination and noncombination groups ( t = −2.872, p < .01), and the optimal cutoff value was 50.5 years. Propensity score matching was completed effectively on a total of 121 patients, using age as the matching factor, comprising 32 cases in the combination group and 80 cases in the noncombination group. The baseline demographic features of the two groups were equivalent after matching ( p > .05), and there was no significant difference in the therapeutic efficacy of 131 I between the two groups ( p > .05). In the subgroup analysis involving patients aged great than 50.5 years, the levothyroxine/weight (µg/kg) was increased in the combination group, and the difference was statistically significant ( p < .05). Conclusion While extrathyroidal ADs may enhance the detection of DTC among elderly women, they have no impact on the clinical characteristics of thyroid cancer or the efficacy of 131 I therapy. ADs may necessitate higher per‐unit dosages of levothyroxine in patients with DTC, regardless of the clinical status. Consequently, it is not essential for nuclear medicine physicians to consider the presence of ADs when designing treatment plans for patients with DTC.