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In the original Whickham survey the prevalence of
thyrotoxicosis which had not been previously diagnosed was
4.7/1000 women in addition to 20 previously diagnosed cases/1,000
women. The condition was ten times more common in women than in
men. Other cross-sectional studies of adult populations in
Sweden, Japan and the UK have shown similar prevalence data.
Sub-clinical thyrotoxicosis, defined on the basis of low serum TSH in the presence of normal T4 and T3 and the absence of any history of Non-Thyroidal Illness or other disease, has a prevalence of between 1% and 6%, partly depending on the sensitivity of the TSH assay used and the cut-off points selected. It is important to acknowledge that in hospital patients suffering from a variety of illnesses TSH may be suppressed and it is not a very good diagnostic test of thyrotoxicosis by itself. Incidence data for overt thyrotoxicosis are comparable in caucasian community studies, although the age- specific rates vary. Thyrotoxicosis due to toxic nodular goitre or autonomous adenoma tends to occur more commonly in the elderly, whereas Graves' disease tends to occur between 20 and 50 years, although it can occur at any age. The mean incidence of thyrotoxicosis in women was approximately 1/1000 survivors per year in the 20 year follow-up of the Whickham survey and no new cases were found in men over that period. The estimated probability of developing thyrotoxicosis in women at a particular time, which is defined as the hazard rate, was calculated as an average of 1/1000/year in women between the age of 35-60 years. Neither antibody titres nor the presence of a goitre when first surveyed was shown to be associated with the development of thyrotoxicosis at follow-up. |
