A 45 year old woman presents to her physician because of a severe "sore throat." Physical examination demonstrates fever and an extremely tender, enlarged thyroid gland, but no throat erythema. Serum thyroid studies demonstrate a mild degree of hypehyroidism. Two months later, the patient is asymptomatic, and thyroid function tests have returned to normal. She never again experiences difficulty with her thyroid function. Which of the following was the most likely cause of her hypehyroidism?

This patient most likely has subacute granulomatous (de Quervain's) thyroiditis, which frequently develops after a viral infection. Microscopically, it is characterized by microabscess formation within the thyroid, eventually progressing to granulomatous inflammation with multinucleated giant cells. Clinically, patients may experience fever, sudden painful enlargement of the thyroid, and/or symptoms of transient hypehyroidism. The disease usually abates within 6 to 8 weeks. Diffuse nontoxic goiter by definition does not produce hypehyroidism. The hypehyroidism of Graves disease does not spontaneously remit. Hashimoto's thyroiditis can cause transient hypehyroidism, but then goes on to cause hypothyroidism. Ref: Lal G., Clark O.H. (2010). Chapter 38. Thyroid, Parathyroid, and Adrenal. In F.C. Brunicardi, D.K. Andersen, T.R. Billiar, D.L. Dunn, J.G. Hunter, J.B. Matthews, R.E. Pollock (Eds), Schwaz's Principles of Surgery, 9e.