Diagnostic cytological features and differential diagnosis of subacute granulomatous (De Quervain's) thyroiditis

Background The aims of the study are to identify the diagnostic cytological features of subacute granulomatous thyroiditis (SGT), to compare our results with previous literature studies, and to investigate the cytological changes in SGT that mimic other thyroid lesions. Methods This retrospective study was conducted with 69 cases. The cytology slides were re-evaluated. The diagnostic cytomorphological features of the disease were identified. The results were compared with the literature. Differential diagnosis of the disease is discussed with the results obtained. Results The diagnostic cytological features consisted of lymphocytes, multinucleated giant cells, loose epithelioid histiocyte groups, granulomas, isolated epithelioid histiocytes, colloid, and neutrophil leukocytes. The highest degree of concordance between our results and the published literature was the presence of giant cells while the lowest was for microfollicles. Some reactive cytological features of SGT were similar to other benign or malignant diseases of the thyroid. Conclusion SGT is a rare and self-limiting disease. Cytological features are not specific. The diagnosis should be confirmed by clinical and laboratory results. Reactive atypia in the early phase of the disease and microfollicles in the late phase may lead to a false cytological diagnosis, thus resulting in unnecessary resection. To prevent such misdiagnoses, cytopathologists should be aware of the reactive cytological changes in this disorder.