Myxoedema coma

Profound hypothyroidism typically presenting with hypothermia, bradycardia and impaired level of conciousness.

Free thyroxine

Thyroxine levels will generally be undetectably low with myxoedema coma. Low but detectable levels occur with lesser degrees of hypothyroidism.

Thyroid stimulating hormone

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.

Full blood count

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.

Urea and electrolytes

Hyponatraemia is commonly seen.

Hyperkalaemia and hyponatraemia may also occur in glucocorticoid deficiency.

Blood glucose levels

Patients with myxoedema may be hypoglycaemic. Monitor blood glucose levels at least 4 hourly.

Liver function test

Liver function should be tested at baseline and may be abnormal with congestive cardiac failure.

Creatinine Kinase

Elevations in CK occur with myocardial damage, but may also reflect rhabdomyolysis.

Bone profile

Hypercalcaemia may occur with severe dehydration or with glucocorticoid deficiency.

Random cortisol

It is useful to send a random cortisol in patients presenting unwell with likely myxoedema prior to starting emergency glucocorticoid therapy.

Serum B12

B12 deficiency may indicate associated pernicious anaemia or coeliac disease.

Chest radiograph

Chest radiograph may reveal cardiomegaly and pleural effusions.

Electrocardiogram

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. 

Arterial blood gas analysis

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.