Reversible changes of the histological abnormalities of the thyroid in patients with painless thyroiditis.

The histological abnormalities on percutaneous needle biopsy of the thyroid were investigated in two patients (cases 1 and 2) with transient thyrotoxicosis and low radioactive iodine uptake by the thyroid and in a patient (case 3) with transient hypothyroidism which might be the consequence of transient thyrotoxicosis. The most characteristic findings of lymphocytic thyroiditis, such as extensive lymphocyte infiltration with collapsed follicles and degeneration of follicular cells of the thyroid, were found in case 1, in whom the thyroid biopsy was performed in the thyrotoxic phase. Ashkanazy cells were not present and fibrosis was not observed in this specimen. Histological examination of the thyroid biopsy specimen, which was obtained in the recovery phase in case 1, revealed well preserved thyroid follicles and slight lymphocytic infiltration. In addition, papillary infoldings of cuboidal epithelium were found in cases 2 and 3, in whom the thyroid biopsy was done in the hypothyroid phase. The follow-up biopsy of the thyroid was performed in the recovery phase in case 3. The biopsy specimen showed focal lymphocytic infiltration and the follicles lined by low cuboidal cells without papillary infoldings. In all biopsy specimens, there was no evidence of subacute thyroiditis, as characterized by granulomatous changes and breakdown of colloid follicles with foreign body giant cell reaction. The present findings revealed that the histological abnormalities, such as lymphocytic infiltration and follicular epithelial changes of the thyroid, observed in the patients with painless thyroiditis, can improve spontaneously during the course of several months.