Alteration of thyroid function in the early stage of subacute thyroiditis

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Abstract
Measurement of serum triiodothyronine (T3), thyroxine (T4), free triiodothyronine (FT3), free thyroxine (FT4), thyroxine-binding-globulin (TGB), antithyroglobulin antibodies (anti-hTg), thyroid 131I uptake and scanning was performed on 12 patients during the early phase of subacute thyroiditis. Serum thyrotropin (TSH) was measured during baseline conditions and following synthetic thyrotropin-releasing-hormone [thyroliberin] (TRH) administration. The stimulation with exogenous TSH was performed on 7 subjects. 131I uptake was depressed in all patients including those with solitary nodules. Free and total hormone concentrations were elevated in the 3 cases with diffuse gland involvement, whereas an increase of T3 alone was present in 3 patients with unilobar involvement. In the latter group and in the 2 patients with a nodular form T4, FT3 and FT4 levels were within normal limits. Interruption of the pituitary-thyroid feed-back mechanism with absence of TSH response to TRH occurred in 11 patients, independent of whether thyroid hormone concentrations were elevated or normal. In 1 patient only with unilateral involvement, TSH responsiveness to TRH was normal while 131I uptake was not riaised by exogenous TSH, indicating diffuse cellular damage. The normal values of FT3 and FT4 found in patients with normal T3 and T4 levels seem to exclude the possibility that the free hormones are responsible for the interrupted feed-back which represents the main cause of suppressed I uptake. However, it is possible that the pituitary-thyroid axis is responding to transient or light increases of free and total T3 and T4 still within their normal range.

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