Absence of Thyroid-Binding Immunoglobulins in Patients with Thyrotropin-Mediated Hyperthyroidism*

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Abstract
Hyperthyroid patients with elevated serum concentrations of TSH [thyrotropin] despite high circulating levels of thyroxine and/or triiodothyronine were recently described. To establish further that these patients have a disorder distinct from Graves'' disease, Ig that inhibit binding to human thyroid membranes (TBI) were measured in the serum of 13 such patients (7 men and 6 women), 7 of whom had pituitary tumors. Serum TSH concentrations ranged from 1.7-160 .mu.U/ml while the patients were hyperthyroid. TBI were also measured in the serum of 21 normal individuals and 14 hyperthyroid patients with apparent Graves'' disease; serum TSH concentrations were less than 0.5 .mu.U/ml in the hyperthyroid patients with Graves'' disease. Six patients with Graves'' disease had ophthalmopathy, and 2 had pretibial myxedema; no patient with inappropriate TSH secretion had ophthalmopathy or pretibial myxedema. TBI in the 21 normal individuals, normalized to 100%, ranged from 82-138%. Of the 14 serum samples from patients with Graves'' disease, 11 were positive for TBI (binding, < 82%; range, 0-78%). Only 2 of 13 patients with inappropriate TSH secretion were positive for TBI. The 1 patient with borderline positive TBI (binding, 76%) had negative thyroid-stimulating Ig, as measured by thyroidal cAMP stimulation. One patient had inappropriate TSH secretion coexisting with positive TBI (binding, 56%) and positive thyroid-stimulating Ig. Apparently TSH-mediated hyperthyroidism is a syndrome distinct from Graves'' disease.

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