Neutropenia associated with different types of thyrotoxicosis: a Japanese cohort study

Abstract Background Graves’ disease (GD) is a relatively common form of thyrotoxicosis. Neutropenia is occasionally observed in patients with GD at the time of diagnosis, and the presence of pre-existing neutropenia may influence the choice of treatment. The prevalence and underlying causes of neutropenia in various types of thyrotoxicosis, including GD, remain unclear. In this study, we evaluated the prevalence of neutropenia in patients with thyrotoxicosis of various etiologies. Methods This was a single-center retrospective observational study. This study was conducted at a tertiary medical institution with a specialized endocrinology center. Adults newly diagnosed with thyrotoxicosis between August 1, 2016, and August 31, 2021, were included. Patients with underlying conditions known to cause cytopenia or those receiving medications that affect neutrophil counts were excluded. Neutropenia was defined as a neutrophil count < 1800.0/µL. Results Of the 373 patients, 188 were eligible for analysis: 114 patients with thyroid-stimulating hormone receptor antibody (TRAb)-positive GD, 12 with TRAb-negative GD, 37 with painless thyroiditis, and 25 with subacute thyroiditis. The median neutrophil counts were significantly higher in the subacute thyroiditis group than in the other groups. Although neutropenia was less frequent in the subacute thyroiditis group than in the other three groups, no significant differences were observed between the groups (7.0%, 8.3%, and 10.8% in the TRAb-positive GD, TRAb-negative GD, and painless thyroiditis groups, respectively). Neutrophil counts were comparable between the TRAb-positive and TRAb-negative GD groups, and FT4 levels were not correlated with neutrophil counts within each group. Conclusion In this retrospective cohort, no statistically significant differences in the prevalence of neutropenia were observed among the different types of thyrotoxicosis. However, given the limited sample size, the small number of neutropenia events, and the imbalance in subgroup sizes, these findings should be interpreted with caution and require confirmation in larger prospective studies. Trial registration Not applicable.