Preserved activation of thyrotropin receptor antibody to stimulate thyroid function despite long-term treatment in euthyroid patients with Graves' disease

Long-term follow-up of patients with hyperthyroidism due to Graves' disease treated with methimazole. Comparison of usual treatment schedule with drug discontinuation vs continuous treatment with low methimazole doses: a retrospective study

Antithyroid drugs may be proposed as the firstline therapy for hyperthyroidism due to Graves' disease since some patients undergo prolonged remission after drug withdrawal. On the other hand, some studies, though controversial, indicated that methimazole (MMI) has some immunomodulating activity. We retrospectively analyzed 384 consecutive patients newly diagnosed with Graves' disease in the years 1990-2002 to ascertain whether long-term therapy with low doses of MMI may prevent relapse of thyrotoxicosis. Two hundred and forty-nine patients were included in our study. The date of reduction of MMI dose to 5 mg/day was considered time 0 for survival analysis. In 121 MMI was discontinued in less than 15 months after time 0 (group D), while in the remaining 128 a daily MMI 2.5-5 mg dose was maintained (group M). One hundred and thirty-five patients were excluded for inadequate response to MMI, relapse of thyrotoxicosis that could be related to an improper withdrawal or reduction of MMI, inadequate or too short followup, iodide contamination, steroid or interferon therapy, pregnancy or post-partum. D and M groups did not differ for clinical and hormonal parameters except age, which was lower in D (p=0.019). Age > vs < 35 yr was relevant in survival analysis; therefore patients were divided in 2 groups according to this age cut-off. In younger patients relapse of thyrotoxicosis occurred in 15 patients of group D 2.4-39.6 months (median 19.0) after time 0, and 8 M after 5.9-40.0 (21.3) months, while 14 D and 5 M maintained euthyroidism until the end of the observation after 31.8-95.3 (56.6) months and 30.4-62.1 (46.5) months, respectively. Survival analysis indicated that the risk of relapse was similar in group D and M. In older patients relapse of thyrotoxicosis occurred in 40 patients of group D after 8.2-65.8 (25.4) months and 29 M after 5.8-62.5 (22.4) months, while 52 D and 86 M maintained euthyroidism until the end of the observation, 20.1-168.0 (46.7) months and 24.1-117.4 (53.4) months respectively. Survival analysis indicated that the risk of relapse was increased in group D. Therefore long-term treatment with low doses of MMI seems to prevent relapse in Graves' disease in patients above 35 yr of age. This should be confirmed in a prospective study.

Induction of stimulating thyrotropin receptor antibodies after radioiodine therapy for toxic multinodular goitre and Graves' disease measured with a novel bioassay

BACKGROUND

Radioactive iodine therapy (RaI) in toxic multinodular goitre (TMNG) has been associated with the occurrence of Graves'-like hyperthyroidism. It has been postulated that pre-existing autoimmunity may contribute to this phenomenon.

OBJECTIVE

To study whether RaI induces thyrotropin receptor stimulating antibodies (TSAbs) in the short term in TMNG and whether pre-existing autoimmunity is relevant.

PATIENTS

Thirty-one patients with relapsing Graves' disease and 17 patients with TMNG, all eligible for RaI.

METHODS

Before and 6 weeks after RaI, sera were collected and analysed for the presence of thyroglobulin (Tg), thyroid peroxidase antibodies (TPO-Abs) and thyrotropin receptor binding antibodies (TBIIs). TSAbs were analysed with a novel high-sensitive luciferase-based bioassay based on the JP-26-26 cell line, which constitutively expresses the TSH receptor.

RESULTS

In Graves' disease, RaI did not induce or increase the levels and proportion of patients with measurable levels of any of the antibodies measured, despite a significant increase in Tg. In contrast, in TMNG, RaI induced TBIIs in three TMNG patients, which was accompanied by measurable TSAbs on one occasion.

CONCLUSIONS

We conclude from the present study that induction of TBIIs and TSAbs may occur shortly after RaI in TMNG and that pre-existing autoimmunity may not be a requirement for the induction of TBIIs, as evidenced by the lack of effect of RaI on TBIIs in Graves' disease.