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Editor,—We wish to raise three important points regarding the diagnosis, aetiology, and management of β-human chorionic gonadotrophin (β-hCG) induced hyperthyroidism.1
(1) β-hCG induced hyperthyroidism is characterised by very high concentrations of β-hCG and these may cross react in some assays for thyroid stimulating hormone (TSH)2 3 giving apparently normal rather than suppressed TSH values. Since many laboratories offer TSH as the first line test in investigating thyroid dysfunction, the diagnosis of β-hCG induced hyperthyroidism may, therefore, be missed.
(2) β-hCG exists as several isoforms depending on carbohydrate content. Desialated isoforms, which are produced more abundantly in cases of β-hCG induced hyperthyroidism, have greater thyrotrophic activity than the commoner sialated isoforms.4 5 Therefore, the quality rather than quantity of β-hCG is important in the development of β-hCG induced hyperthyroidism. This also explains why pregnancy, with high β-hCG concentrations comparable to those reported in this case, is not usually associated with thyrotoxicosis.
(3) Tumour β-hCG induced hyperthyroidism may require standard antithyroid treatment, but almost invariably responds to effective tumour chemotherapy. Tumour relapse may also be associated with recurrence of the thyrotoxicosis.2
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