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Impaired Intrathyroidal Iodine Organification and Iodine-Induced Hypothyroidism in Euthyroid Women with a Previous Episode of Postpartum Thyroiditis^*

ELIO ROTI, ROBERTA MINELLI, ELIANA GARDINI, LINA BIANCONI, TAURO NERI, GILBERTO GAVARUZZI, GIORGIO UGOLOTTI, DIANA SALVO and LEWIS E. BRAVERMAN

Centro per lo Studio, Prevenzione, Diagnosi e Cura delle Tireopatie, Cattedra di Endocrinobgia, Universita di Parma; Cattedra di Genetica Medica, Universita di Parma; Seruizio di Medicina Nucleare Nucleare, Ospedali Riuniti di Parma Servizio di Medicina Nucleare, Ospedale S. Maria Nuoua di Reggio Emilia Italy Division of Endocrinology and Metabolism, University of Massachusetts Medical School Worcester, Massachusetts 01605

Address all correspondence and requests for reprints to: Elio Roti, M.D., Cattedra di Endocrinologia, Universita di Parma, Via Gramsci 14, 43100 Parma, Italy.

Postpartum thyroiditis (PPT) is common and occurs in 1.7 to 16.7% of pregnant women, depending upon the study population. Most of these women develop transient hypothyroidism and thyroid function usually returns to normal. We have studied 11 euthyroid women with a previous history of PPT to determine the incidence of subtle defects in thyroid function measured by iodide-perchlorate (I-CIO₄) discharge tests and TRH tests and to determine whether these women would develop iodide-induced hypothyroidism. Seven (64%) had positive I-CIO₄ discharge tests and 5 (46%) had an abnormally high TSH response to TRH. Thyroid antimicrosomal and antithyroid peroxidase were positive in 8 women (73%) with a previous episode of PPT. The administration of pharmacological amounts of iodide (10 drops of saturated solution of potassium iodide daily) for 90 days to these 11 women resulted in elevated basal and TRH stimulated serum TSH concentrations in 8 (72.7%) compared to TSH values during iodide administration to women who had never been pregnant. Antimicrosomal and antithyroid peroxidase concentrations did not change during iodide administration. These findings strongly suggest that euthyroid women with a previous episode of PPT have permanent subtle defects in thyroid hormone synthesis and are inordinately prone to develop iodide-induced hypothyroidism, similar to findings previously reported in euthyroid subjects with Hashimoto's thyroiditis, with a previous episode of painful subacute thyroiditis, or previously treated with radioactive iodine or surgery for Graves' disease.

^* Presented in part at the 10th International Thyroid Congress, The Hague, February 3–8, 1991. This work was supported in part by Grants 88.00.628.0,89.04244.04,90.01540.CT04 from Consiglio Nazionale delle Ricerche (Rome); Grant "Patologia della Tiroide: Indagine dei fattori Etiopatogenetici" of Ministero Pubblica Istruzione 40% (Rome, Italy); Grant Ricerca Finalizzata Regione Emilia Romagna 1988–1990; and Grant DK-18919, NIDDK, NIH, Bethesda, MD.

Recipient of a fellowship from Associazione Volontaria Promozione Ricerca Tumori (A.VO.PRO.RI.T.), Parma, Italy.

Received March 7, 1991.

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