ESPE Abstracts (2015) 84 P-2-565

Metamorphic Thyroid Autoimmunity in Down Syndrome: From Hashimoto's Thyroiditis to Graves' Disease and Beyond

Tommaso Aversaa, Mariella Valenzisea, Mariacarolina Salernob, Andrea Corriasc, Lorenzo Iughettid, Giorgio Radettie, Filippo De Lucaa & Malgorzata Wasniewskaa

aDepartment of Pediatric, Gynecological, Microbiological and Biomedical Sciences, University of Messina, Messina, Italy; bDepartment of Translational Medical Sciences, Pediatric Endocrinology Unit, University ”Federico II” of Naples, Naples, Italy; cDepartment of Pediatrics, University of Turin, Turin, Italy; dDepartment of Pediatrics, University of Modena and Reggio Emilia, Modena, Italy; eDepartment of Pediatrics, Regional Hospital, Bolzano, Italy

Background: During the last years, it has been sporadically reported that Graves’ disease (GD) and Hashimoto’s thyroiditis (HT) may follow one another in the same individuals, due to a sequential phenotypic conversion from GD to HT or vice versa.

Objective and hypotheses: To shed further light on the specific relationships between Down syndrome (DS) and metamorphic thyroid autoimmunity.

Method: We have reconstructed the conversion process from HT to GD in a selected population consisting of 12 DS individuals aged between 3.0 and 13.5 years at HT diagnosis and between 4.1 and 19.9 years at GD diagnosis. All the patients underwent a treatment with methimazole (MMI), at a dose that was periodically adjusted on the basis of clinical findings and thyroid function tests.

Results: After MMI treatment onset all patients exhibited, at varying time intervals, a prolonged clinical and biochemical remission of hyperthyroidism. In eight/12 patients this treatment is still being continued 2–7 years after its initiation. The mean MMI dosage needed to maintain euthyroidism in these eight patients was 0.12±0.02 mg/kg per day. In the remaining four patients MMI was withdrawn from 1.9 to 7 years after its initiation and no relapses were recorded 2.0–2.1 years after its withdrawal. All these four patients developed, from 0.1–0.3 years after MMI withdrawal, a biochemical picture of overt hypothyroidism and needed treatment with LT4, that is now being continued since 2.0–2.1 years. No patients needed non-pharmacological therapies, such as surgery or radioiodine ablation.

Conclusion: i) DS children may be incline to manifest over time a phenotypic metamorphosis from HT to GD; ii) A share of GD children with DS may subsequently fluctuate from hyperthyroidism to hypothyroidism; iii) In DS HT presentation is absolutely peculiar; iv) in DS GD is characterized by a mild biochemical and clinical course.