Profound hypothyroidism typically presenting with hypothermia, bradycardia and impaired level of conciousness.
Thyroxine levels will generally be undetectably low with myxoedema coma. Low but detectable levels occur with lesser degrees of hypothyroidism.
Thyroid stimulating hormone (TSH) levels will generally be extremely high in myxoedema: >50mU/l.
Unless the patient is known to have pituitary disease, TSH levels within or close to the normal range exclude severe hypothyroidism.
This is a useful indicator of general health and underlying disease, and essential in the collapsed patient.
Macrocytosis may be seen with profound hypothyroidism, but may reflect undiagnosed pernicious anaemia.
Normocytic normochromic anaemia and eosinophilia may be seen with glucocorticoid deficiency.
Hyponatraemia is commonly seen.
Hyperkalaemia and hyponatraemia may also occur in glucocorticoid deficiency.
Patients with myxoedema may be hypoglycaemic. Monitor blood glucose levels at least 4 hourly.
Liver function should be tested at baseline and may be abnormal with congestive cardiac failure.
Elevations in CK occur with myocardial damage, but may also reflect rhabdomyolysis.
Hypercalcaemia may occur with severe dehydration or with glucocorticoid deficiency.
It is useful to send a random cortisol in patients presenting unwell with likely myxoedema prior to starting emergency glucocorticoid therapy.
B12 deficiency may indicate associated pernicious anaemia or coeliac disease.
ECG must be performed in the collapsed patient.
Bradycardia, decreased voltages, non specific St and T segment changes, varying degrees of heart block, a prolonged QT interval and J waves may all be present with myxoedema. Conversely, myocardial ischaemia may also precipitate myxoedema and so typical ST segment changes may also be present.
Chest radiograph may reveal cardiomegaly and pleural effusions.
Patients may become hypoxic and hypercapnoeic. Peripheral probes to assess oxygen saturations may also be unreliable in the hypothermic patient and so arterial blood gas analysis is therefore advisable.