Subclinical hypothyroidism in paediatric population treated with levothyroxine: a real-world study on 2001-2014 Italian administrative data.

Objective: To estimate the prevalence of subclinical hypothyroidism (SH) among children, by using levothyroxine low dosage as disease proxy, and to describe prescription pattern.

Design: An historical cohort study was performed through administrative databases of 12 Italian Local Health Units covering 3,079,141 inhabitants. A cohort of children (aged 0-13 years) was selected in the period 2001-2014. A subgroup of new users (aged 0-9 years) was identified and followed up for 5 years.

Methods: The prevalence was provided as mean value of the whole period, as annual trend, by patient gender and age. Demographic details, information on levothyroxine dosage, comorbidities and co-medications were provided. Therapy duration and medication persistence were evaluated among new users.

Results: 644 children treated with levothyroxine low dosage was selected, with a mean annual prevalence of 0.20 per 1000 children. The temporal trend of prevalence was stable, with a slight reduction in the 2005-2008. Prevalence by age showed an increase after 10 years. Patients were treated with an average annual dose of 4290 µg/year and 66.9% of children were affected by comorbidities. Among 197 new users, 62.9% received therapy only for one year, whereas out of those treated two or more years, 89.0% resulted persistent to the therapy.

Conclusions: This study provides real-world epidemiology of SH among children, and it depicts the clinical and therapeutic characteristics of these subjects. Its findings showed that the SH treatment of this disorder was widely variable, also due to lack of evidence concerning paediatric population.