It is important to determine whether elevated thyroid hormone levels are from the causes listed in this article rather than from excess synthesis of thyroid hormone. Generally, the conditions described here are temporary and therefore do not require definitive therapy, such as thyroid surgery, radioactive iodine treatment, or antithyroid therapy. Radioactive iodine treatment and antithyroid therapy are never appropriate for these forms of subacute thyroiditis.
Conditions to consider in the differential diagnosis of subacute thyroiditis include the following:
Acute hemorrhage into a thyroid cyst, nodule, or neoplasm
Trauma- or palpation-induced thyroiditis
Riedel or fibroid thyroiditis
Toxic thyroid adenoma
Toxic multinodular goiter
Acute suppurative thyroiditis
The last disorder in the above list, acute suppurative thyroiditis, is most commonly caused by a bacterial infection of the thyroid via the conduit of a congenital pyriform sinus fistula. This pain and swelling in the early stages can be confused with subacute thyroiditis. A study by Masuoka et al of 60 patients with acute suppurative thyroiditis found that careful imaging can provide clues to an early diagnosis of this condition, which can develop into a life-threatening endocrine emergency. 
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