The High Proportion of Painless Thyroiditis as a Cause of Thyrotoxicosis in Korea

Abstract

Background and Objectives: The most common cause of thyrotoxicosis is Graves’ disease (GD), while painless thyroiditis (PT) comes in second. In Korea, the treatment of choice for GD is antithyroid drugs (ATDs). Since most cases of PT spontaneously improve, an accurate diagnosis is very important for the proper management of patients presenting with thyrotoxicosis. Materials and Methods: Ninety-nine thyrotoxic patients were routinely checked with 99m Technetium (99mTc) thyroid scan except in pregnant or lactating women. We assessed the patients’ clinical characteristics, serum levels of free T4 (FT4), thyroid stimulating hormone (TSH), thyroid peroxidase antibody (TPOAb), thyroglobulin antibody (TGAb), thyrotropin-binding inhibitory immunoglobulin (TBII), and findings of 99mTc thyroid scan. Results: Among the 99 thyrotoxic patients, 69 were diagnosed with GD and 30 had PT. All of the patients with GD, diagnosed by scan, improved clinically and the thyroid hormone returned to normal with ATDs. All patients with PT improved spontaneously without ATDs. TPOAb and TGAb were positive in 13 (43.3%) and 20 (66.7%) patients with PT, respectively. TPOAb and TGAb were positive in 45 (65.2%) and 44 (63.8%) patients with GD, respectively. TBII was positive in only 73.5% of GD, and was entirely negative in the PT group. Mean FT4 level in GD was higher than in PT, but some patients with PT showed the highest level of FT4. Conclusion: PT accounted for a very high proportion of thyrotoxicosis in this study. All parameters investigated such as age, sex, goiter size or nature, level of FT4, TPOAb or TGAb, and TBII were unable to differentiate GD from PT. Considering the increased proportion of PT in the current study, we recommend routine thyroid scan in all thyrotoxic patients except in pregnant or lactating women.