Prevalence and aetiology of hypothyroidism in the young

Aims - To define the prevalence of hypothyroid disease in children and young people, and describe its aetiology. Methods - We identified all patients on the Medicines Monitoring Unit (MEMO) database in the Tayside region of Scotland who had received two or more prescriptions for thyroxine during the study period (January 1993 to December 1995). Using this as a surrogate marker of hypothyroidism, we calculated the prevalence of hypothyroidism in those aged less than 22 years. Main outcome measures were prevalence of thyroxine prescription, estimated prevalence of hypothyroidism, and aetiology of the hypothyroidism (determined from case records, and biochemistry and immunology databases). Results - Of 103 500 residents aged less than 22 years, 140 were identified as receiving thyroxine on prescription, giving a population prevalence of 0.135%. The ratio of male to female was 1:2.8. Acquired hypothyroidism was the commonest aetiology found in 73%, 66% of which had an autoimmune basis. The prevalence of congenital hypothyroidism was 0.027%. Seven had received treatment for malignancy (two primary thyroid). Fifteen per cent of patients had no record of secondary care follow up in Tayside. Conclusion - The overall prevalence of hypothyroidism in young people less than 22 years of age is 0.135%, and in the group aged 11-18 years it is 0.113%; these values axle at least twice those of previous estimates. This suggests an increase in autoimmune thyroid disease, similar to the rising prevalence of type 1 diabetes, possibly indicating a rising incidence of autoimmunity in young people.