Thyroid function in the early stage and during the course of subacute thyroiditis

In a study on 44 patients with subacute thyroiditis (SAT), high thyroid hormone levels were found in 66% of cases during the early stage of the disease related to the extension of the lesion. ft4 was most frequently elevated. TSH response to TRH was suppressed in all but one patients independent of thyroid hormone levels. Clinical thyrotoxicosis was always mild. Reserve T3 was significantly above normal only in patients with elevated thyroid hormones (group A), probably because of the large availability in T4, and it was positively correlated with T3 and T4. The rT3 to T3 ratio was also significantly increased. TBG was within the physiologic range in all instances. Following recovery all the a forementioned parameters returned within normal limits. Thirteen patients, belonging to group A, were monotored by sequential measurements of T3, T4, FT3, FT4, rT3, TBG and basal TSH during the course of the disease while either on corticosteroid therapy or after recovery. They showed a similar trend: after the acute phase all hormones fell to normal, T3 and FT3 to hypothyroid values for approximately 30 days to eventually revert to the normal range. TSH was still whitin the normal limits, with a peak value about the 40th day. These changes seem to reflect the peripheral disposal of T4 since thyroid hormone release ceases during the initial phase of SAT. However, cannot to be excluded a contributory effect similar to that observed in acute febrile illness together with an inhibitory action of glucocorticoid on monodeiodination