SERUM THYROTROPHIN RESPONSE TO THYROTROPHIN RELEASING HORMONE AND THE CONCENTRATION OF FREE THYROXINE IN SUBACUTE THYROIDITIS

Abstract

ABSTRACT Fourteen patients with subacute thyroiditis were studied. In the acute stage 6 were overtly and 2 equivocally hyperthyroid. Total thyroxine (T4) or protein-bound iodine (PBI) was elevated in 10 patients out of 14 and absolute free thyroxine (AFT4) in 10 out of 13 cases. The serum thyrotrophin (TSH) values ranged from 1.3 to 7.9 μU/ml, all but one being below 4.0 μU/ml (normal range 1.6–6.9 μU/ml). There was no response in serum TSH to thyrotrophin releasing hormone (TRH) in 9 subjects tested in the acute stage, irrespective of whether they were clinically hyperthyroid or euthyroid. This indicates that in the acute stage of subacute thyroiditis the thyroid hormone level is increased sufficiently to inhibit TSH release. In 8 patients the TRH stimulation test was carried out serially at 2 to 3 monthly intervals but in 5 only after 2 to 6 months. In a few patients the serum TSH level rose above the normal upper limit. The response to TRH became normal within 2 to 5 months but in one patient only after a period of exaggerated response indicative of temporary subclinical hypothyroidism. In one patient the response was still exaggerated one year after the acute phase, indicating that normalization of the thyroid-pituitary relationship may be a very slow process.