Scintigraphic findings of the thyroid in euthyroid ophthalmic Graves' disease

The scintigraphic findings of the thyroid were analyzed in patients with euthyroid ophthalmic Graves' disease known to have some thyroid-related abnormalities.

Technetium-99m-pertechnetate images of the thyroid from 38 euthyroid ophthalmic Graves' disease patients with small, soft or nonpalpable goiter were analyzed.

Scan images showed homogeneous (even) and nonhomogeneous (uneven) 99mTc uptake in 20 and 16 patients respectively. Poor images due to low uptake were observed in two patients. Six patients displayed alterations in scintigraphic appearance from even to uneven patterns after T3 suppression test. Statistical analysis revealed that the uneven pattern was more frequently observed in euthyroid ophthalmic Graves' disease patients than in 26 patients with hyperthyroid Graves' disease who were euthyroid during antithyroid drug therapy (p < 0.005). The scintigraphic heterogeneity was correlated with reduced uptake as well as a higher ratio of the uptake values after T3 treatment to the pretreatment values. Scintigraphically, hot or warm lesions were observed in most cases showing the uneven pattern (16/22; 73%). Rather low titers of antithyroglobulin, antimicrosomal antibodies and TSH-binding inhibitor immunoglobulins were detected in only 4 (10.5%), 7 (18.4%) and 12 (31.6%) patients respectively, while the prevalence of thyroid-stimulating antibodies (TSAb) was as high as 86.8% (33/38). The scintigraphic heterogeneity did not correlate with the detection of these antibodies but did correlated with the severity and duration of ophthalmopathy.

The presence of functioning follicular cells with some autonomy that were heterogeneously distributed in the thyroid was observed in about half the euthyroid ophthalmic Graves' disease patients. Chronic stimulation by TSAb may be the underlying mechanism for these findings.