The role of ultrasound in distinguishing between IgG4‑positive Hashimoto’s thyroiditis and primary thyroid lymphoma: a pilot study

Abstract

IgG4-positive Hashimoto’s thyroiditis (IgG4-HT) is an aggressive HT subtype that may be misdiagnosed as primary thyroid lymphoma (PTL) due to overlapping clinical and imaging features. This study aimed to evaluate the utility of ultrasound for non-invasive differentiation between IgG4-HT and PTL. Data from 13 IgG4-HT and 19 PTL patients (all pathology-proven) were retrospectively collected. Clinical characteristics, laboratory findings, and sonographic features were compared between the two groups. IgG4-HT patients were younger than PTL patients (40.31 ± 11.38 vs. 69.00 ± 10.25 years, P  < 0.001). No significant differences in sex distribution, compressive symptoms, or thyroid function were found. On ultrasound, PTL showed larger anterior-posterior thyroid diameters (left lobe: 3.00 ± 1.29 cm vs. 1.65 ± 0.32 cm, P  < 0.001; right lobe: 3.19 ± 1.24 cm vs. 1.62 ± 0.44 cm, P  < 0.001), more frequent linear hyperechoic areas (89.5% vs. 30.8%, P  = 0.002), posterior acoustic enhancement (89.5% vs. 15.4%, P  < 0.001), and very hypoechoic patterns (78.9% vs. 0%, P  < 0.001). Extrathyroidal extension was observed exclusively in the PTL group (10.5%). Distinct ultrasound features—including marked anteroposterior enlargement, very hypoechoic echogenicity, and posterior acoustic enhancement—may assist in raising suspicion for PTL. Ultrasound may contribute to the differentiation of PTL from IgG4-HT during the initial evaluation, which may facilitate early recognition and timely histopathological confirmation.