Fig. 1Representative two cases with rapid response and slow response. Each point represents changes of free thyroxine according to prescribed dose of methimazole. From linear regression model based on points in each patient, correlation coefficients of all patients were obtained and considered as responsiveness to methimazole. Closed circles and solid line indicate a patient with rapid response (correlation coefficient=0.215), and open triangles and dashed line indicate a patient with slow response (correlation coefficient=0.011).
Fig. 2Serial changes in free thyroxine levels in each patient during the follow-up period. Almost patients showed normalization of free thyroxine within about 2 months, regardless of initial free thyroxine level. Two dashed lines represent the upper and lower boundaries of the reference range for free thyroxine (25.0 and 10.0 pmol/L, respectively).
Fig. 3Distribution of responsiveness to methimazole. The dashed vertical line indicates the median value of responsiveness.
Fig. 4Receiver operating characteristic (ROC) curves for the responsiveness to methimazole. (A) ROC curve of thyroid binding inhibitory immunoglobulin (TBII) titer at initial diagnosis for the responsiveness. (B) ROC curve of free thyroxine level at initial diagnosis for the responsiveness. AUC, area under the curve.
Table 1Baseline Characteristics between Groups According to Methimazole Responsiveness
Characteristic |
Total |
Rapid responder |
Slow responder |
P value |
No. of case |
99 |
50 |
49 |
|
Age, yr |
44.0±13.5 |
46.1±15.2 |
41.9±11.3 |
0.126 |
Male sex |
40 (40.4) |
22 (44.0) |
18 (36.7) |
0.595 |
Duration of treatment, mo |
27.0 (6.0–84.0) |
29.0 (6.0–84.0) |
26.0 (10.0–80.0) |
0.429 |
Presence of a goiter |
|
|
|
0.320 |
None |
28 (28.3) |
16 (32.0) |
12 (25.5) |
Small (<40 g) |
37 (37.1) |
21 (42.0) |
16 (34.0) |
Medium to large (≥40 g) |
32 (33.0) |
13 (26.0) |
19 (40.4) |
Smoking |
27 (27.3) |
13 (26.0) |
14 (28.6) |
0.951 |
Initial dose of methimazole, mg |
24.5±6.0 |
24.7±5.3 |
24.4±6.7 |
0.797 |
Initial free T4, pmol/L |
48.9±21.9 |
59.2±24.5 |
38.6±11.6 |
<0.001 |
TBII titer, IU/L |
36.6±74.4 |
52.6±93.9 |
20.3±41.9 |
<0.001 |
Table 2Clinical Factors Predicting Rapid Response to Methimazole
Variable |
Univariate |
Multivariate |
OR |
95% CI |
P value |
OR |
95% CI |
P value |
Age, yr |
1.024 |
0.994–1.056 |
0.128 |
1.020 |
0.981–1.063 |
0.321 |
Female sex |
0.739 |
0.328–1.651 |
0.462 |
0.290 |
0.059–1.248 |
0.106 |
Goiter |
|
|
|
|
|
|
Small |
0.984 |
0.362–2.659 |
0.975 |
0.336 |
0.083–1.231 |
0.110 |
Medium to large |
0.513 |
0.180–1.423 |
0.294 |
0.194 |
0.083–0.864 |
0.038 |
Smoking |
0.878 |
0.359–2.135 |
0.774 |
0.283 |
0.049–1.389 |
0.133 |
Initial free T4 |
2.925 |
1.859–5.058 |
<0.001 |
2.813 |
1.721–5.186 |
<0.001 |
Log TBII titer |
4.276 |
1.811–11.389 |
0.002 |
4.217 |
1.457–13.802 |
0.011 |