ADVERSE-EFFECTS OF THYROID-HORMONES

The adverse health effects of thyrotoxicosis have been carefully docum ented and most practitioners are familiar with the clinical consequenc es for the patient. Until recently, many patients experienced the adve rse effects of excessive thyroxine dosages, which can now be avoided b y the application of highly sensitive immunometric assays for monitori ng serum thyrotrophin (thyroid-stimulating hormone; TSH) levels, Howev er, sensitive monitoring of serum thyrotrophin levels has led to the f requent recognition of biochemical subclinical hyperthyroidism (isolat ed suppression of thyrotrophin). Because of the increased recognition of this condition, the adverse effects of thyroxine therapy can be div ided into those associated with subclinical hyperthyroidism and those associated with the euthyroid state. Investigation of the potential cl inical consequences of thyrotrophin-suppressing dosages of thyroxine h as dominated studies over the last decade, with less attention being g iven to euthyroid patients, It appears that the adverse effects of thy roxine are considerably more common when serum thyrotrophin has been s uppressed, They are usually manifested in older patients as increased bone mineral loss in postmenopausal women and as cardiac effects in pa tients with intrinsic heart disease, These patients may have subtle be havioural alterations and other clinically silent organ effects that o ccur infrequently. Children who are euthyroid while taking thyroxine o ccasionally develop pseudotumour cerebri shortly after starting hormon e replacement for hypothyroidism. Otherwise, thyroxine dosages that re nder patients euthyroid, as evidenced by thyrotrophin values that are within the normal range, rarely cause adverse effects. Thus, avoidance of dosages that cause thyrotrophin suppression, when not clinically i ndicated, is the primary approach to the management of these adverse e ffects.