Myxoedema coma: response of thyroid hormones with oral and intravenous high-dose L-thyroxine treatment.

Myxoedema coma is a medical emergency with high mortality. In this study, clinical response and plasma variations of thyroid hormones were analysed in 7 patients, 6 presenting with myxoedema coma and one with myxoedema ileus. These patients were treated with intravenous or oral l-thyroxine (l-T4). 1000 μ l-T4 iv were administered in two patients. Within 3 h, plasma T4 and triiodothyronine (T3) reached a peak upper normal range, then diminished slowly during 5–9 days. The 5 remaining patients were treated with 500 μg l-T4 po on the first day, then 100 μg l-T4 daily by mouth. Plasma T4 and T3 increased slowly, remaining in hypothyroid range but clinical response (assessed on mental status, pulse rate and body temperature) occurred within 24–72 h. Cortisone therapy was used in 3 patients. Two patients died of myocardial infarction, or septicemia, one while receiving cortisone therapy and i.v. l-T4, another one treated only by oral l-T4. This study suggests: 1) oral absorption of l-T4 is variable, but clinical response occurs quickly even in myxoedema ileus; 2) the intravenous route involves high peaks of plasma T4 and T3; 3) peripheral conversion of T4 to T3 allows gradually T3 delivery to organ systems, even if only l-T4 is used and 4) initial and daily dosage determinations need further studies.