Endocrine Abstracts

Full replacement dose of thyroxine should not be administered initially to elderly hypothyroid patients, those with a history of coronary artery disease and to patients with long-standing severe hypothyroidism. Here, we present a 27-year-old lady with profound longstanding hypothyroidism, who developed cardiac failure on a small dose of thyroxine.

She presented to her General Practitioner with longstanding symptoms of lethargy, poor concentration, constipation and irregular menstrual period. Investigations revealed TSH 334 miu/l and Free T₄ <5.2 pmol/l. She was commenced on thyroxine 50 mcg daily. Three days later she developed chest tightness and dyspnoea. On examination in coronary care unit she was found to be wheezy with bibasal crackles and bilateral pitting oedema. Thyromegaly was present and had delay in relaxation phase of ankle reflex. An ECG demonstrated T wave inversion of the lateral leads, and a CXR was consistent with pulmonary oedema. Troponin T was negative, TPO antibody >1000 IU/ml and creatine kinase 1150 μ/l. An Echocardiogram reported global dyskinesia with reduced left ventricular function. She was treated with intravenous diuretics and thyroxine was initially discontinued. Once stable, thyroxine was re-introduced very slowly, starting at 12.5 mcg and increased cautiously over several weeks. She was asymptomatic at 3 months with TSH 6.28 miu/l and FT₄ 11.1 pmol/l. Repeat echocardiogram was reported normal. Introduction of thyroxine replacement in a profoundly hypothyroid patient is likely to have resulted in significant cardiac dysfunction.

Thyroxine improves cardiac function in patients with hypothyroidism and increases cardiac output, decreases systemic vascular resistance, decreases end-diastolic volume and increases myocardial oxygen consumption. To avoid precipitating acute myocardial ischemia and/or cardiac failure, thyroxine dose should be very gradually titrated. This case highlights that it is important to be mindful of cardiac complications when initiating thyroxine replacement in longstanding severe hypothyroidism.