03 December 2008
The detection of thyrotropin-binding inhibitory immunoglobulins (TBII) and/or thyroid-stimulating antibody (TSAb) has been reported in some patients with painless thyroiditis (PT) or subacute thyroiditis (SAT). However, its mechanism is unknown. TBII and TSAb measured using cultured FRTL-5 thyroid cells were evaluated in 18 patients with PT, 11 patients with SAT and a patient with SAT-like symptoms. In PT, we detected both TBII and TSAb activities in only 1 patient. This case had first come to our attention with subclinical hypothyroidism and had already had weakly positive TSAb activity (205.9%) 1 year before the present onset of PT. This patient had a transient thyrotoxicosis with a low uptake (24 h) of <sup>123</sup>I (4.3%) and 821.0% TSAb activity, and subsequently developed a transient subclinical hypothyroidism. Even after 2 years, she still had positive TSAb activity (382.3%). In SAT, TBII and TSAb activities were not detected during the courses of any patients. A patient with transient thyrotoxicosis, who had a high uptake (30 min) of <sup>99m</sup>Tc (5.6%) and SAT-like symptoms (painful tenderness on right thyroid lobe and markedly accelerated erythrocyte sedimentation rate), showed positive activities of TBII (34.9%) and TSAb activity (1,366.9%). Histological findings by thyroid needle biopsy performed in the thyrotoxic phase showed coexistence of granulomatous inflammatory changes and hyperplasia with papillary folds of some residual follicular cells. Thus, when TSAb activity was detected in patients with PT or SAT-like symptoms, the possibility of an association of PT or SAT with Graves’ disease is also suggested.