PatientPlus articles are written by UK doctors and are based on research evidence, UK and European Guidelines. They are designed for health professionals to use, so you may find the language more technical than the condition leaflets.
Synonym: myxoedema crisis
Myxoedema coma is the extreme manifestation of (usually untreated) hypothyroidism. It is one of a relatively small number of endocrine emergencies, and it is a rare, but potentially fatal disorder. It does not necessarily involve the presence of pretibial oedema or of coma.
Myxoedema coma can be difficult to diagnose and successfully treat. Even if promptly treated it has a mortality of 50%.
In a patient who has untreated or undertreated hypothyroidism several physiological changes take place to compensate for the lack of thyroid activity. This ability of the body to compensate for deficiency of T4 and T3 may, however, be overwhelmed – for example, by infection, drugs, other diseases or hypothermia. The resulting state is referred to as ‘myxoedema coma’ despite the fact that the patient may not be comatose or display the skin changes of myxoedema (hence the alternative term ‘myxoedema crisis’).
Myxoedema coma can be regarded as a form of decompensated hypothyroidism in which the adaptations of the body to untreated hypothyroidism fail to maintain homoeostasis and become overwhelmed by hypothermia, infection or other precipitating factors. These adaptations include peripheral vasoconstriction to maintain core body temperature.
This process of adaptation and eventually failing function, affects all organs, including the brain, heart, lungs, kidney and gastrointestinal tract (see ‘Clinical features found in myxoedema coma’, below).
Factors which may precipitate myxoedema coma
- Hypothermia (common precipitant).
- Urinary tract infections
- Drugs acting on the central nervous system
- Other significant physiological challenges:
- Gastrointestinal haemorrhage
- Cerebrovascular disease
- Surgery, anaesthetics or trauma
- Accidents, burns
- Respiratory depression and retention of carbon dioxide
- Myxoedema coma is around four times more common in women than in men (reflecting the higher incidence of hypothyroidism in women, which has a prevalence of 8% in women aged over 50).
- Myxoedema coma occurs almost exclusively in patients over 60 years of age.
- In communities with iodine deficiency (mountain regions of Asia, Africa and South America) the prevalence of hypothyroidism is higher. It is therefore likely that the incidence of myxoedema coma is also higher in these populations.
- The condition presents more often in the winter months (90% of cases present in the winter).This seasonal variation probably relates to age-related loss of temperature sense, combined with lower heat production secondary to hypothyroidism.
- It usually presents in patients with long-standing hypothyroidism, which may be undiagnosed or inadequately treated due to lack of monitoring or poor compliance.
- Other factors known to precipitate myxoedema coma include hypoglycaemia, infection, trauma, haemorrhage and change of medication.