Introduction:
Subacute thyroiditis (SAT) is typically a self-limiting, inflammatory disease. Patients can experience hypothyroidism during or after an episode. We examined the clinical characteristics based on laboratory and imaging studies in patients with SAT and possible factors contributing to the development of permanent hypothyroidism after SAT.

Material and methods:
We retrospectively examined the medical records of patients diagnosed with SAT at one medical facility in Turkey. Patients known to have previous thyroid disease, those with < 6 months of follow-up after resolution of SAT, and those who lacked sufficient data for analysis were excluded. Of the 283 patients identified, 119 met all the inclusion criteria. We extracted data on demographics, laboratory tests, neck pain and other symptoms, ultrasonography findings, medication use, and SAT recurrence. We examined the relationships between these variables and the development of permanent hypothyroidism.

Results:
The patients were 42 years old on average, and 78% were women. Most patients (70%) described flu-like symptoms before neck pain started; accordingly, 57% had initially visited a specialty other than endocrinology before SAT was diagnosed, and 28% had received antibiotics for misdiagnosed upper respiratory tract infection. In all, 10 patients (8.4%) developed permanent hypothyroidism after SAT. These patients had received steroids significantly longer than those without permanent hypothyroidism (mean 17.7 weeks vs. 8.9 weeks; p = 0.021). Development of hypothyroidism was significantly lower among patients with thyrotoxicosis.

Conclusions:
The diagnosis of SAT can be challenging. Patients who require longer-term steroids after SAT and who have recurrent SAT should be closely monitored for development of hypothyroidism.