Diagnosis in a patient with known hypothyroidism, who stopped treatment a long time ago and shows typical clinical features, is easy.
It is more difficult when hypothyroidism has not yet been diagnosed. The association of altered mental status, hypothermia, and a precipitating event should lead to suspicion, particularly in an elderly patient ( Nicoloff.and LoPre.sti.1993). Hyponatremia, hypoxia, hypercapnia, and anemia are always present in this condition (Table
1) (MadPtti. etaL 1995). Specific treatment should be started after blood samples have been obtained for assays of thyroid- stimulating hormone, free tri-iodothyronine, free thyroxine, and cortisol. The diagnosis is positive when the results are in agreement with primary hypothyroidism, i.e. elevated plasma thyroid-stimulating hormone and dramatic reduction of both free tri-iodothyronine and free thyroxine, thus excluding a 'euthyroid sick syndrome' or low tri-iodothyronine syndrome. The latter syndrome is observed in critically ill patients with normal thyroid function and low plasma free tri-iodothyronine ( Rpt[etaL
19.93). In more severe illnesses low plasma free thyroxine may also be present, but plasma thyroid-stimulating hormone remains normal. At present, the results of thyroid hormone assays can be obtained within a short time, for example within an hour by chemiluminescence immunoassay.
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Table 1 Biological signs in myxedema coma
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