Endocrine Abstracts

Introduction: Patients with Down syndrome are vulnerable to autoimmune thyroid disease and progression from Graves’ disease (GD) to Hashimoto’ thyroiditis or vice-versa may be more frequently seen in this population, specially at a younger age. In the last years questions have been raised regarding the distinction of this metamorphic scenario from a single entity: autoimmune thyroiditis with TRAbs that trigger opposite functional actions.

Case report: A female patient with trisomy of the 21st chromosome was evaluated at age 14 due to thyrotoxicosis. She was diagnosed with GD based on clinical signs/symptoms, elevated FT4/FT3 and supressed TSH with TRAb positivity (TRAb 19.7 < 1.5 UI/ml) and absence of thyroid nodularity in the US. She was given appropriate dosages of methimazole to maintain euthyroidism until age 18 when treatment was stopped due to raising TSH. Given the sustained hypothyroid pattern she was started on levothyroxine. Primary hypothyroidism due to Hashimoto’ thyroiditis was diagnosed at age 20 based on the hypoechogenic thyroid pattern and positivity for serum thyroglobulin and thyroid peroxidase autoantibodies. During the 10 years of follow up, thyroid function tests showed marked fluctuations from supressed to high TSH (< 0.02 to 33 µUI/ml) despite the relatively stable dosages of levothyroxine, FT4 and FT3 within reference range and recurrent denial of non-adherence to treatment. More interestingly, TRAb titres ranged from 71–529 (< 1.5 UI/ml) without clear association of titres with severity of thyroid function status. She is now 32 years old and has been euthyroid for the last year with a stable dosage of 88 mg of levothyroxine, positive TPOAb, TgAb and TRAb. Last US showed a small 5 ml hypoechoic gland with fibrous septa (RL 11 × 9.4 × 24 mm and LL 13 × 11 × 26 mm, AP × T × L), suggesting chronic atrophic thyroiditis.

Conclusions: Autoimmune TRAb positive atrophic thyroiditis is being increasingly recognized. Fluctuations in TSH due to shifting/competing stimulatory and inhibitory TRAbs are typical. We postulate that given the current low thyrocyte mass reserve the patient will maintain a more stable thyroid function. Additional tests as scintigraphy (specially I-123) and functional TRAb assays, unfortunately not widely available, shall be helpful to a better understanding and categorization of autoimmune thyroid disorders.