Endocrinol Metab.  2017 Jun;32(2):281-287. 10.3803/EnM.2017.32.2.281.

Free Thyroxine, Anti-Thyroid Stimulating Hormone Receptor Antibody Titers, and Absence of Goiter Were Associated with Responsiveness to Methimazole in Patients with New Onset Graves' Disease

• Choi HS
• Yoo WS

• KMID: 2384088
• DOI: http://doi.org/10.3803/EnM.2017.32.2.281

Abstract

BACKGROUND
Anti-thyroid drug therapy is considered a treatment of choice for Graves' disease; however, treatment response varies among individuals. Although several studies have reported risk factors for relapse after initial treatment, few have assessed responsiveness during the early treatment period. Our study aimed to identify the clinical characteristics for responsiveness to methimazole.
METHODS
We included 99 patients diagnosed with Graves' disease for the first time. Drug responsiveness was defined as the correlation coefficients between decreasing rates of free thyroxine level per month and methimazole exposure dose. According to their responsiveness to treatment, the patients were classified into rapid or slow responder groups, and age, sex, free thyroxine level, and thyrotropin binding inhibiting immunoglobulin (TBII) titers were compared between groups.
RESULTS
The mean patient age was 44.0±13.5 years and 40 patients were male (40%). The mean TBII titer was 36.6±74.4 IU/L, and the mean free thyroxine concentration was 48.9±21.9 pmol/L. The rapid responder group showed higher TBII titer and free thyroxine level at diagnosis, while age, sex, smoking, and presence of goiter did not differ between the two groups. Logistic regression analyses revealed that high level of serum thyroxine, high titer of TBII, and absence of goiter were significantly associated with a rapid response, while age, sex, and smoking were not significant factors for the prediction of responsiveness.
CONCLUSION
In patients with new onset Graves' disease, high level of free thyroxine, high titer of TBII, and absence of goiter were associated with rapid responsiveness to methimazole treatment.

Keyword

Graves disease; Responsiveness; Methimazole; Thyrotropin binding inhibiting immunoglobulin; Free thyroxine

MeSH Terms

Diagnosis
Drug Therapy
Goiter*
Graves Disease*
Humans
Immunoglobulins
Logistic Models
Male
Methimazole*
Recurrence
Risk Factors
Smoke
Smoking
Thyrotropin
Thyroxine*
Immunoglobulins
Methimazole
Smoke
Thyrotropin
Thyroxine

Figure

• 

  Fig. 1 Representative 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. 2 Serial 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. 3 Distribution of responsiveness to methimazole. The dashed vertical line indicates the median value of responsiveness.

• 

  Fig. 4 Receiver 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.

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