Overt Versus Subclinical Hypothyroidism: An Ultrasound-Based Comparison of Thyroid Nodule Burden and Parenchymal Heterogeneity

Background: Whether overt hypothyroidism carries a different structural thyroid profile from subclinical disease is still uncertain. We therefore compared thyroid ultrasound findings in the two groups, focusing on nodule burden and parenchymal heterogeneity. Methods: This retrospective study included 210 adults with hypothyroidism: 53 with overt disease and 157 with subclinical disease. Demographic, laboratory, and thyroid ultrasonography data were reviewed. Ultrasound outcomes were any thyroid nodule, nodule burden, nodules ≥1 cm, cystic or solid nodules, and parenchymal echotexture. Multivariable models were adjusted for age and sex. Results: Patients with overt hypothyroidism were older than those with subclinical hypothyroidism (median age: 52 vs. 43 years; p<0.001). Heterogeneous parenchyma was more common in patients with overt hypothyroidism than in those with subclinical hypothyroidism on unadjusted analysis (46/53 (86.8%) vs. 108/157 (68.8%); p=0.011) and remained independently associated with overt hypothyroidism after adjustment (adjusted OR: 2.94; 95% CI: 1.20-7.17; p=0.018). By contrast, the groups did not differ significantly in the prevalence of any thyroid nodule (26/53 (49.1%) vs. 71/157 (45.2%); p=0.637), nodule burden, nodules ≥1 cm, cystic nodules, or solid nodules. Age, rather than hypothyroidism category, was the main determinant of nodularity: each 10-year increase in age was associated with higher odds of any thyroid nodule (adjusted OR: 1.35; 95% CI: 1.13-1.62; p=0.001) and nodules ≥1 cm (adjusted OR: 1.59; 95% CI: 1.23-2.07; p<0.001). Conclusion: Overt hypothyroidism was associated with more frequent parenchymal heterogeneity, but not with greater thyroid nodule burden. Thyroid nodularity and larger nodules were more closely related to age than to the hypothyroidism category.