Few Patients with Subclinical Hyperthyroidism Progress to Overt Hyperthyroidism over 7 yr

Vadiveloo T , Donnan PT , Cochrane L , Leese GP

The Thyroid Epidemiology, Audit, and Research Study (TEARS): the natural history of endogenous subclinical hyperthyroidism.

J Clin Endocrinol Metab. 2011 Jan;96(1):E1-8. Epub 2010 Oct 6.

This study was to define the rates of progression from subclinical hyperthyroidism (SH) to frank hyperthyroidism and normal thyroid function. Record-linkage technology was used retrospectively to identify patients with SH in the general population of Tayside, Scotland, from January 1, 1993, to December 31, 2009. . All Tayside residents with at least two measurements of TSH below the reference range for at least 4 months from baseline and normal free T(4)/total T(4) and total T(3) concentrations at baseline were included as potential cases. Using a unique patient identifier, data linkage enabled a cohort of SH cases to be identified from prescription, admission Online Pokies, and radioactive iodine treatment records. Cases younger than 18 yr of age were also excluded from the study : The status of patients was investigated at 2, 5, and 7 yr after diagnosis.

SCH was identified in 2024 cases, a prevalence of 0.63% and an incidence of 29 per 100,000 in 2008. Most SH cases without thyroid treatment remained as SH at 2 (81.8%), 5 (67.5%), and 7 yr (63.0%) after diagnosis. Few patients (0.5-0.7%) developed hyperthyroidism at 2, 5, and 7 yr. The percentage of SH cases reverting to normal increased with time: 17.2% (2 yr), 31.5% (5 yr), and 35.6% (7 yr), and this was more common in SH patients with baseline TSH between 0.1 and 0.4 mU/liter. Very few SH patients develop frank hyperthyroidism, whereas a much larger proportion revert to normal, and many remain with SH.