Thyroid stimulating immunoglobulins in Graves' disease with goitre growth, low thyroxine and increasing triiodothyronine during PTU treatment
Abstract. In 50 consecutive patients with Graves' disease treated with PTU, 7 (group 1) developed increasing goitre in spite of unmeasurable TSH. Thyroid variables were compared with those from 10 controls with an ordinary response to PTU (group 2). Serum T4 decreased in group 1 from 246 ± 47 nmol/l (mean ± sd) to 40 ± 9 nmol/l after 6 weeks of PTU treatment and continued to be below the normal range during the next 4 months. In group 2 serum T4 decreased from 190 ± 35 to 88 ± 47 nmol/l and stayed in the normal range. Serum T3 was normalized in both groups after 6 weeks but increased to values above the normal range in group 1 after that time. In spite of unmeasurable TSH during the 6 months of treatment in group 1, thyroid volume, determined ultrasonically, increased significantly from 60 ± 29 to 93 ± 68 ml (P < 0.05), but was unaltered in group 2 about 25 ml. Thyroid stimulating antibodies (TSAb) measured by adenylate cyclase activation (normal below 109%) decreased in group 2 from 117 ± 23 to 90 ± 17% (P <0.01) (6 months of therapy), but increased significantly in group 1, from 201 ± 47% to a maximum value of 234 ± 69% (P < 0.05). TSH binding inhibitory immunoglobulins (TBII) (given as per cent inhibition, normal below 26%) decreased in group 2 from 43 ± 29 to 29 ± 27% (P < 0.05) but were unaltered high in group 1,66 ± 25% before therapy and 57 ± 26% after 6 months of therapy. A positive correlation was found between thyroid volume and TSAb and TBII levels (P < 0.05, P < 0.05) before treatment as well as during the treatment period of 6 months. In 5 of 7 patients of group 1 either 131I therapy or subtotal thyroidectomy were necessary to control the disease. It is proposed that TSAb and TBII remaining abnormal in this subgroup of patients with Graves' disease, might in part explain the unusual response to PTU-treatment.