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Mo, Ryu, Kim, and Kim: The High Proportion of Painless Thyroiditis as a Cause of Thyrotoxicosis in Korea
Original Article

Clin Exp Thyroidol 2015;8(1):61-66.

Published online: 4 May 2015

DOI: https://doi.org/10.11106/cet.2015.8.1.61

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

Sang Il Mo, A Jeong Ryu, Yeo Joo Kim, Sang Jin Kim

Department of Internal Medicine, Subdivision of Endocrinology and Metabolism, Soonchunhyang University, Cheonan, Korea

Correspondence: Sang Jin Kim, MD, Department of Internal Medicine, Soonchunhyang University Cheonan Hospital, 23-20 Bongmyung-dong, Cheonan 330-721, Korea Tel: 82-41-570-3672, Fax: 82-41-574-5762, E-mail: ksj1113@schmc.ac.kr

Received 27 July 2014       Accepted 3 February 2015

Copyright © 2015, the Korean Thyroid Association.

This is an open-access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0/), which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

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.

Keywords: Graves' disease, Painless thyroiditis, Thyroid scan, Thyrotoxicosis

References

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Fig. 1.
Typical findings of thyroid scan of Graves' disease (left) and painless thyroiditis (right).
jkta-8-61f1.tif
Fig. 2.
The mean FT4 level of Graves' disease was higher than painless thyroiditis. The normal range of FT4 was 0.93-1.7 ng/dL. Three of 30 patients showed very high level of FT4 in PT and 5 of 59 patients showed highest level of FT4 in Graves' disease.
jkta-8-61f2.tif
Fig. 3.
Individual serum total T3/free T4 ratios in Graves' disease and painless thyroiditis. Total T3/free T4 ratio in patients with Graves' disease was significantly (p=0.044) higher than that in patients with painless thyroiditis.
jkta-8-61f3.tif
Table 1.
Baseline characteristics of thyrotoxic patients
Painless thyroiditis (n=30) Graves' disease (n=69) p value
Age (years) 44.03±12.40 44.03±12.44 0.999
Sex     0.166
Male (%) 12 (40.0) 18 (26.1)  
Female (%) 18 (60.0) 51 (73.9)  
Symptoms     0.001
Negative (%) 20 (66.7) 21 (30.4)  
Positive (%) 10 (33.3) 48 (69.6)  
Goiter     0.030
Negative (%) 17 (56.7) 23 (33.3)  
Positive (%) 13 (43.3) 46 (66.7)  
Consistency of goiter     0.918
Soft (%) 10 (56.7) 36 (78.3)  
Hard (%) 3 (23.1) 10 (21.7)  
Thyroid function test      
Total T3 (ng/dL) 213±94 369±150 <0.001
Free T4 (ng/dL) 2.87±1.68 4.44±1.84 <0.001
Total T3/Free T4 78.83±20.29 85.31±18.74 0.044
TPOAb     0.042
Negative (%) 17 (56.7) 24 (34.8)  
Positive (%) 13 (43.3) 44 (63.8)  
TGAb     0.782
Negative (%) 10 (33.3) 25 (36.2)  
Positive (%) 20 (66.7) 44 (63.8)  
TBII     <0.001
Negative (%) 30 (100) 18 (26.1)  
Positive (%) 0 (0) 50 (72.5)  

Continuous variables were analyzed by Mann-Whitney test. Categorical variables were analyzed by Pearson's Chi-square test. TBII: thyrotropin-binding inhibitory immunoglobulin, TGAb: thyroglobulin antibody, TPOAb: thyroid peroxidase antibody

Table 2.
The sensitivity and specificity of differential cut-off point of Graves' disease from painless thyroiditis
AUC (%) Cut-off point Sensitivity (%) Specificity (%)
Total T3 (ng/dL) 85.0 233.5 83.6 80.0
Free T4 (ng/dL) 80.9 3.21 67.2 86.7
Total T3/Free T4 63.1 75.21 77.0 60.0

AUC: area under the curve

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