Endocrine Abstracts

Objective: Some patients with Graves’ disease (GD) respond faster to antithyroid drugs (ATD) than others. Our aim was to study if levels of autoantibodies to the TSH-receptor (TRAb), thyroid-stimulating immunoglobulin (TSI), thyroid peroxidase antibodies (anti-TPO) and/or clinical factors influence the early response to anti thyroid drugs (ATD) in women with GD.

Methods: This was a longitudinal cohort study of 65 women with GD and fT4 ≥50 pmol/l (reference range 12-22 pmol/l), and/or total T3 ≥6 nmol/l (reference range 1.3-3.1 nmol/l). All started with tiamazol 5 mg 3 x 2 and decrease of fT3 and fT4 was evaluated after median 8 days. Groups were created for patients with antibody levels over and under the median for TRAb and TSI and patients positive or negative for TPO. Decrease in fT4/T3/day of ATD was compared between groups. We also assessed duration of symptoms, goitre, age and smoking. Variables were correlated to the decrease of fT3/fT4/day of ATD.

Results: Patients with high TRAb decreased more in fT3 (median 2.1 and 1.0 P < .01 and fT4 (median 4.0 and 2.1 P < .001) per day of ATD compared to those with low TRAb. The same was true for TSI for fT3 (median 2.3 and 1.0, P < .001) and fT4 (median 4.0 and 2.0, P < .0001). The decrease of hormones correlated with levels of TRAb (fT3 ρ= 0.45, P < 01, fT4 ρ=0.48, P < .001) and of TSI (fT3 ρ=0.52, P < .001, fT4 ρ=0.51, P < .0001). In those positive for anti-TPO the decrease in fT3 (median 1,8 and 0.9, P < .01) and fT4 (median 4.1 and 1.9, P < .01) per day of ATD was greater compared to TPO negative patients but initial hormone levels did not differ. Levels of anti-TPO correlated with the decrease of fT3 (ρ=0.50, P < .01) and fT4 (ρ=0.48, P < .01) but not with initial hormone levels, TRAb or TSI. No difference could be found between those with none or mild goiter compared to those with moderate to significant goiter or between smokers (n =8) and non-smokers. No correlation was found between the decrease of hormones and age.

Conclusion: That GD patients with high TRAb, TSI and thyroid hormones respond more promptly to ATD compared to those with lower levels is not surprising. However, the greater response in those positive for anti-TPO cannot be explained by this and poses questions to the mechanism of action of the drugs and a possible influence of anti-TPO in GD.