An Estimation of the Incidence of Thyroiditis Among Girls in Primary Care in Spain

Abstract

Objective: As for other auto-immune processes, thyroiditis is monitored after vaccinations. The aim was to estimate the baseline incidence of thyroiditis among girls, before investigating papillomavirus vaccination as a potential risk factor. Methods: Observational cohort study including girls aged 9-18 years and registered between 2002-2016 in the Spanish Primary Care Database for Pharmacoepidemiological Research. Girls were followed until a thyroiditis occurred, 19 years of age, left the cohort, died, or the study ended. Anonymized records were reviewed for diagnosis confirmation (endocrine discharge letter and/or free-text comments) in a random sample. Incidence rate (IR) per 10 5 person years (/10 5 py) was estimated. Results: The cohort numbered 480,169 girls, of whom 641 had a record of thyroiditis: 346 autoimmune thyroiditis; 17 thyroiditis of other types; and 278 unspecified. Incidence of recorded thyroiditis increased with age, from 23.96 at age 9 years to 47.91 at age 14 years, and stabilized around 31.06-34.43 among girls aged 15-18 years. Of the 98 records reviewed, 60.2% were ‘confirmed’ cases, 32.7% ‘possible’ and 7.1% were discarded. After correction for discarded cases, IR=20.83 ‘confirmed’ cases, increasing to 32.12/10 5 py when ‘confirmed’ plus ‘possible’ cases were included. Between 2002-2005, incidences were lower (16.28 and 20.93 cases/10 5 py) than in the period 2007-2016 (21.17 and 33.78 cases/10 5 py) for ‘confirmed’ and ‘confirmed’ plus ‘possible’, respectively. Conclusion: Two-thirds of the recorded thyroiditis included confirmatory evidence. The incidence of thyroiditis among girls increased with age and in the later period, and remained stable among girls aged 15-18 years.

Risk Factors for Thyroiditis: A Cohort Study to Illustrate What Factors Might be Present Among Girls and Female Adolescents Scheduled to Human Papillomavirus Vaccination

“…The precision of the thyroiditis recording and date versus the true diagnosis were assessed and described elsewhere [5]. It was estimated that around 60% of thyroiditis cases included in the current analysis would be confirmed in the PCP records, 33% would not have information apart from the diagnosis to confirm or discard it (so-called 'possible' cases in the paper of reference), and 7% would be discarded had we manually reviewed all of them looking for confirmatory written evidence.…”

“…Thyroiditis has been found the most frequent diagnosis among female adolescents and young adults hospitalized for diseases of presumed autoimmune origin (53 per 10 5 adolescents and 389 per 10 5 women) [4]. In Spain, we estimated that among girls aged 9-18 years between 20.83-32.12 new cases of thyroiditis were diagnosed every 10 5 girls-years in 2002-2017 [5]. Thyroid hormones play an important role in childhood growth and are involved in the maturation and metabolism of certain organs such as the skeleton and brain where they influence the process of myelination of the nervous system [6].…”

“…The Spanish Primary Care Database for Pharmacoepidemiological Research (BIFAP) [17], constitutes a powerful source of information for research of the natural history of thyroiditis [5]. Among potential risk factors, we aimed to assess the prevalence of several…”