High prevalence of subclinical thyroid nodular disease in autopsies from Mexico with low frequency of NIFTP

Introduction: The prevalence of thyroid nodular disease (TND) varies depending on study type. Nevertheless, a study including autopsies of patients from all over the country, covering almost three decades, is required to deepen our understanding of benign, borderline, and malignant lesions after the World Health Organization 2022 update. This study aimed to identify the prevalence of follicular TND (FTND), borderline, and malignant nodules in autopsies from a third-level hospital in Mexico City, as well as to determine the association between salt iodination and thyroid nodule genesis. Methods: Autopsies performed between 1992 and 2019 were considered if archived thyroid remnants and clinical data were available. Cases with known premortem thyroid pathology were excluded. Nodules were considered diagnosed if gland morphology was grossly distorted. Results: The study included 487 autopsies, of which 276/59.2% were women. The mean age was 46.6 years. Of 487 glands, 266 (55%) had TND. Nodular glands had a higher weight than normal glands (17.8 vs. 16.1 g), with a 1.9:1 female-to-male ratio. No increase in the prevalence of nodules was observed after 2004 when salt iodination was regulated (0.40 vs. 0.39; p = 0.969). The median age of patients with FTND was 49 years for men and 51 years for women. Papillary thyroid carcinoma was observed in 44/9.4% glands, and the recently characterized non-invasive follicular thyroid neoplasm with papillary-like nuclear features (NIFTP)/an indeterminate lesion was only identified in seven (1.5%) cases. Conclusions: TND was not associated with salt iodine regulation in Mexico, and prospective studies are needed to explain this finding in this country. Understanding the prevalence of subclinical FTND, NIFTP, and carcinomas is relevant and can contribute to reducing the rate of overdiagnosis in thyroid pathology.