Endocrine Abstracts

Introduction: The possibility of progression of subclinical hyperthyroidism (SH) to overt hyperthyroidism (OH) is a critical point in deciding whether to treat this situation.

The aim of this study is to evaluate the rate of progression of SH to OH and the factors influencing this outcome.

Methods/design: This is a retrospective study at an endocrine referral service in Northern Greece. Data from patients with SH diagnosed between 1996 and 2011 were extracted from the department’s electronic database. Patients with past history of thyrotoxicosis treated with radioiodine, surgery or antithyroids, thyroiditis, pregnancy/postpartum state, severe illness and pituitary disease were excluded.

Results: Forty patients (37 females/3males) aged 53.9±14.3 years (range 25–76) were included. Mean TSH values at baseline were 0.19±0.13 mIU/l. In 18 patients (45%) the diagnosis was subclinical Graves’ disease (GD), 13 (32.5%) multinodular toxic goitre (MTG) and 9 (22.5%) toxic adenoma (TA).

Progression to OH was seen five patients, (12.5%), in two (11.1%) with GD, two (22%) with TA and one (7.7%) with MTG, during a mean follow-up time of 34.2±21.3 months. OH was observed in 4/36 (11.1%) at 1 year, 1/23 (4.5%) at 2 years, 0/15 (0%) at 3 years and 1/17 (5.9%) at 5 years. Three of five patients with SH progressed to OH in 6 months.

Interestingly, eight patients at 1 year (22%) normalized thyroid function, 5 (23%) at 2 years, 4 (27%) at 3 years and 6 (35%) at 5 years of follow-up. Five of seven (71.4%) with available follow-up data remained euthyroid during follow-up.

Conclusions: GD was the most common etiology of SH. A very small proportion of patients progressed to OH over 5 years. However, a considerable amount of patients with SH returned to normal thyroid function either for the remainder of follow-up, or only to return to SH state.