Jerry, a 48-year-old white man, is referred to endocrinology for abnormal results of thyroid tests performed four weeks ago (see table for values). Two months ago, Jerry developed an upper respiratory infection (URI) with fever, odynophagia, and anterior neck discomfort. His symptoms resolved after two weeks; however, he has since developed fatigue and nervousness.
The remaining review of systems is unremarkable. Medical history is negative. Jerry denies any factors that can affect thyroid function: He does not take thyroid medication, OTC thyroid supplements, amiodarone, lithium, or interferon-α, does not have high iodine intake, and has not undergone head/neck irradiation. There is no personal or family history of thyroid disease, organ-specific autoimmune disease (ie, vitiligo, myasthenia gravis, or Sjögren syndrome) or systemic autoimmune disease (rheumatoid arthritis, systemic lupus erythematosus, or progressive systemic sclerosis).
Vital signs are stable. On physical examination, his thyroid gland is firm, with slight enlargement of the left lobe and mild tenderness. There are no palpable nodules or cervical adenopathy. The remainder of the exam is unremarkable.
Lab studies (see table) reveal an elevated erythrocyte sedimentation rate (ESR) and suppressed TSH, with normal free thyroxine (T4) and free triiodothyronine (T3) levels. His thyroid peroxidase antibody (Anti-TPO) is negative. Radioactive iodine uptake (RAIU) reveals a low 24-hour uptake of 4% (normal, 5% to 30%).
Jerry is given the presumptive diagnosis of subacute thyroiditis (SAT). He is advised that the condition will progress through multiple phases—from the initial thyrotoxicosis to euthyroidism
to transient hypothyroid—before resolution and is educated on the symptoms and signs to watch for. Since he presented in a euthyroid phase, with only mild anterior neck tenderness, no treatment is indicated. He is instructed to follow up for thyroid function testing in four to six weeks and to call with any symptomatic changes.
Two months later, Jerry returns with complaints of ongoing fatigue, unintentional weight gain, and “mental fog.” Physical exam findings are unremarkable except for a small, firm thyroid gland without the tenderness elicited previously. Labwork reveals an elevated TSH with low free T4 and free T3. He is again counseled regarding the natural history of SAT and reassured that his symptoms will abate as his thyroid hormone levels normalize. He is advised to continue the plan of follow-up testing every four to six weeks.
Approximately eight weeks later, Jerry’s thyroid function studies indicate normal levels, and he is notified of the results. Jerry comments that his symptoms have completely resolved and he is back to feeling like his usual self. He is discharged to follow-up as needed.
What is subacute thyroiditis?