Correlation study on the efficacy of ¹³¹I therapy for Graves disease with ¹³¹I conversion rate, residual ¹³¹I level, and clinical data

Objective To explore the correlations of the ¹³¹I conversion ratio, post-therapeutic thyroid ¹³¹I residual activity, and clinical data with the therapeutic efficacy of ¹³¹I therapy in patients with Graves disease, and to identify independent influencing factors to guide individualized treatment.

Methods A retrospective cohort study was performed. A total of 1 117 patients with Graves disease who received ¹³¹I therapy at the First Affiliated Hospital of Kunming Medical University between September 2017 and September 2022 were enrolled. According to data completeness, patients were divided into a core cohort (938 patients with complete clinical and follow-up data) and an extended cohort (179 patients with additional data on thyroid ¹³¹I residual activity). Patients were classified into the clinically cured group and the non-clinically cured group in accordance with "Clinical Guidelines for ¹³¹I Therapy of Graves′ Hyperthyroidism (2021 Edition)". Between-group comparisons of quantitative data were conducted using the Mann-Whitney U rank-sum test; categorical data were compared using the χ² test or Fisher′s exact test. Spearman correlation analysis was applied to assess associations between variables and treatment response. Multivariate binary logistic regression was used to screen independent predictors of ¹³¹I therapeutic efficacy.

Results Within the core cohort, 440 patients were assigned to the clinically cured group, whereas 498 were allocated to the non-clinically cured group. The 2 h/24 h and 4 h/24 h ¹³¹I conversion ratios in the clinically cured group were lower than those in the non-clinically cured group (0.59% (0.48%, 0.73%) vs. 0.80% (0.62%, 0.94%); 0.78% (0.67%, 0.90%) vs. 0.96% (0.82%, 1.03%); Z=−11.836, −12.427; all P<0.001). Both ratios were negatively correlated with therapeutic efficacy (r=−0.387, −0.406, all P<0.001), with the 4 h/24 h ¹³¹I conversion ratio showing a stronger correlation than the 2 h/24 h ¹³¹I conversion ratio. Univariate analysis demonstrated that 20 clinical variables including age were associated with treatment outcome. Multivariate regression identified 6 independent influencing factors (all P<0.05): 4 h/24 h ¹³¹I conversion ratio (OR=0.082, highest weight of influence), age (OR=0.981), concomitant Hashimoto′s thyroiditis (OR=1.453), thyroid weight (OR=0.964), combined post-¹³¹I antithyroid drug (ATD) therapy (OR=0.477), and thyroglobulin (Tg) level (OR=0.999). In the extended cohort, 110 patients comprised the clinically cured group, and 69 were in the non-clinically cured group. Thyroid ¹³¹I residual counts at 2-month and 3-month follow-up after therapy were significantly lower in the cured group than in the non-clinically cured group (5594.0 (2020.0, 15862.0) cpm vs. 11512.0 (4458.0, 31669.0) cpm; 77.5 (18.3, 367.3) cpm vs. 353.0 (54.5, 779.0) cpm; Z=−3.024, −3.729; all P<0.001), and both measurements were negatively correlated with efficacy (r=−0.227, −0.279; all P<0.01).

Conclusions The 4 h/24 h ¹³¹I conversion ratio and thyroid ¹³¹I residual counts at 2 and 3 months after treatment, age, thyroid weight, post-¹³¹I combined ATD therapy, and Tg level were negatively correlated with ¹³¹I therapeutic efficacy. Concomitant Hashimoto′s thyroiditis was positively correlated with treatment response.