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

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.