Recovery of the thyroid function in patients with atrophic hypothyroidism and blocking type TSH binding inhibitor immunoglobulin

The prognosis of atrophic hypothyroidism with blocking type TSH-binding inhibitor immunoglobulin was studied. Among 45 patients (16 males and 29 females) with overt hypothyroidism (serum TSH greater than 40 mU/l) without goitre, thyroid autoantibody to microsomal antigen was positive in 38 or 84.4%, and 4 or 8.9% had TSH-binding inhibitor immunoglobulin, which was shown to be a TSH-stimulation blocking antibody by cAMP production assay using cultured porcine thyroid cells. Thyroidal radioactive iodine uptake was low and thyroid hormone replacement therapy was required. Long-term follow up of 2 patients with strongly positive TSH-binding inhibitor immunoglobulin for 2 to 7 years, however, revealed recovery of the thyroid function after steroid therapy or spontaneously with iodide restriction, respectively, correlating with decrease in both TSH-binding inhibitor immunoglobulin and TSH-stimulation blocking antibody activities. Thyroidal radioactive iodine uptake became normal and histological examination of the thyroid in one patient revealed well-preserved thyroid follicles with lymphocytic infiltration. Recovery of thyroid function can be expected with a decrease in TSH-binding inhibitor immunoglobulin activity in atrophic hypothyroidism, which is not necessarily the end stage of chronic thyroiditis.