medwireNews: Girls with Hashimoto thyroiditis who also have Turner syndrome may be at particularly high risk of developing abnormal thyroid function over the long term, report researchers.

Despite similar thyroid function at baseline, study participants who had Hashimoto thyroiditis with Turner syndrome were significantly more likely than those with Hashimoto thyroiditis alone to have hypo- or hyperthyroidism 5 years after diagnosis.

However, Filippo De Luca (University of Messina, Italy) and co-researchers stress that decline of thyroid function may occur in Hashimoto thyroiditis patients irrespective of the presence of Turner syndrome. By the end of the 5-year follow-up, only 56.8% of the 132 patients without Turner syndrome still had normal thyroid function. Of the others, 30.3% had subclinical hypothyroidism and 12.9% had overt hypothyroidism.

But of the 66 patients with Turner syndrome, only 34.8% had normal thyroid function, with 13.6% developing subclinical hypothyroidism, 47.0% overt hypothyroidism and 4.6% hyperthyroidism.

At baseline, levels of thyroid-stimulating hormone (TSH) and free thyroxine were similar between girls with and without Turner syndrome. Five years later, patients with Turner syndrome had significantly higher TSH levels than those without, at 7.8 versus 3.4 mIU/L, and lower free thyroxine levels, at 11.5 versus 14.9 pmol/L.

These differences persisted after accounting for age and baseline levels of thyroid peroxidase autoantibodies, despite the researchers saying that this apparent effect of Turner syndrome “is not easily explained from a pathophysiological point of view”.

The influence of Turner syndrome was not linked to a specific karyotype, they note in Hormone Research in Paediatrics.

The team therefore advocates “strict monitoring” of thyroid function in Turner syndrome patients with Hashimoto thyroiditis, even if they initially have euthyroidism. “Annual measurements of serum TSH levels might be advisable for this purpose”, they say.

De Luca and team also highlight that Hashimoto thyroiditis shifted towards Graves’ disease in 4.6% of the patients, who required methimazole therapy.

They say this is “not surprising”, since a switch to hyperthyroidism has been reported both in Hashimoto thyroiditis patients and in girls with Turner syndrome.

By Eleanor McDermid

Hormone Res Paediatr 2016; Advance online publication

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