Epidemiology of subtypes of hyperthyroidism in Denmark: a population-based study

Objective: Few population-based studies have described the epidemiology of subtypes of hyperthyroidism. Design: A prospective population-based study, monitoring two well-defined Danish cohorts in Aalborg with moderate iodine deficiency (nZ311 102) and Copenhagen with only mild iodine deficiency (nZ227 632).Methods: A laboratory monitoring system identified subjects with thyroid function tests suggesting overt hyperthyroidism (low s-TSH combined with high s-thyroxine or s-triiodothyronine).

For all subjects, we collected information on medical history, thyroid scintigraphy and thyroid hormone receptor antibody (TRAb) measurement. Information was used to disprove or verify primary overt hyperthyroidism and to subclassify hyperthyroidism into nosological disorders.Results: From 1997 to 2000 (2 027 208 person-years of observation), we verified 1682 new cases of overt hyperthyroidism.

The overall standardized incidence rate (SIR) per 100 000 person-years was 81.6, and was higher in Aalborg compared with Copenhagen (96.7 vs 60.0, P