Myxoedema coma

Myxoedema coma, the most extreme manifestation of hypothyroidism, belongs in either "Acute Thyroid crises" as a Level 1 topic from Section 2.1.9 in the second edition of the CICM Syllabus for the Second Part Examination. It would be tempting to put it into the L2 category of "Other thyroid disorders", because it is almost by definition never acute, but then the frequency of its appearance in the past papers suggests that the examiners attribute a greater level of importance to it. Plus authors keep referring to it as a crisis. It is a state characterised by three major features:

• Decreased level of consciousness
• Defective thermoregulation
• Cardiovascular collapse

This condition is well described in articles dating back to the 1950s.. Concerned about the lack of recent publications, new authors have stepped up to fill the void in the new century. From the exam perspective, it certainly seems to occupy a position of eminince in the minds of the examiners, perhaps out of proportion to its prevalence. Among the past papers, the following SAQs have explored myxoedema coma:

• Question 16 from the first paper of 2024 (mostly management)
• Question 13 from the second paper of 2018 (again management)
• Question 30.1 from the first paper of 2014 (also some management)
• Question 15.1 from the first paper of 2008 (recognise it from biochemical features)
• Question 7 from the first paper of 2006 (recognise it from biochemical features)

Of the sources, probably the best is Farooq & Khan (2021) for quick revision, and Donangelo & Braunstein (2021) for actual explanations.

Most cases tend to present during cold weather, where the ambient temeprature lowers the threshold for encephalopathy. These cases tend to be elderly women, fond of self-negect, given to squalor in the autumn of their life.

Presentation of myxoedema coma

A great article form the American Family Physician goes through the various clinical features of myxoedema coma, which I have tabulated:

Another, different version of the same material can be presented using a crude alphabetical structure, if that is the kind of thing you like. Papers by Farooq & Khan (2021) and Donangelo & Braunstein (2021) were used to flesh this out:

Airway features

• Macroglossia
•  Oedema (myxoedema) of the nasopharynx and larynx
• Goitre displacing the airway

Respiratory features

• A "puffy" face, propensity to sleep apnoea
• Reduced hypoxic respiratory drive
• Decreased ventilatory response to hypercapnia

Cardiovascular features

• Bradycardia
• Pericardial effusion
• Cardiogenic shock
• Prolonged PR interval
• Decreased QRS voltages, especially in the limb leads
• Prolonged QT
• Deep T-wave inversions

Neurological features

• Decreased level of consciousness
• Seizures (in up to 25%)
• Psychosis or depression ("myxoedema madness")

Electrolyte abnormalities

• Hyponatremia
• Hyposmolarity
• Hypoglycaemia
• Elevated protein levels on LP
• High serum cholesterol
• Raised CK (increased muscle permeability)

Renal consequences

• Bladder atony and urinary retention

Gastrointestinal features

• Anorexia, nausea, abdominal pain
• Constipation,  ileus, all the way to megacolon

Haematological features

• Normocytic normochromic anaemia from decreased erythropoiesis 

Immunological features

• Hypothermia, which masks fever

Other associated examination findings:

• Hypothermia
• Periorbital oedema
• Coarse, sparse hair
• Non-pitting oedema

The ECG changes of myxoedema were recently trotted out into Question 12.2 from the first paper of 2018, where the presentation of the 73 year old female patient was in a state of dishevelment and with hypothermia. The CICM examiners used this LITFL ECG for the paper, which comes from the LITFL page on ECG changes associated with hypothyroidism. Specifically, they used "Example 2 - Myxoedema coma (after treatment)". Presumably they thought the deep T-wave changes in the pre-treatment example would distract the trainees and everybody would put "AMI" as one of their main differentials.

Management of myxoedema coma

Management of this condition consists of the following steps:

• Replace thyroid hormone - preferably IV
  • loading dose is 300-400μcg
  • a rising body temperature and normalising cardiovascular parameters alert you to the success of your management strategy
  • IV T3 is preferred mostly because of the atonic bowel, where absorption is likely to be erratic. IV T4 has been used as well, but apparently it is less effective because it has lower intrinsic activity. Plus if there is some concurrent illness (an there always is) the T4  is not converted to T3 because of reduced 5′-deiodinase activity. 
• Replace corticosteroids - there is usually a concomitant adrenal insufficiency. One would use a "stress dose".
• Correct the sodium: this is usually a hypervolemic hyponatremia which resembles that of CCF (in fact, it is because of exactly the same mechanism: poor cardiovascular performance leads to ADH and aldosterone driven retention of water and sodium, with a resulting hypervolemic hyponatremia. Because the patient is usually obtunded, one is obliged to correct a particularly low sodium with hypertonic saline, being careful not to demyelinate the CNS.
• Good solid supportive management:  this seemed necessary in the CICM answer to Question 13 from the second paper of 2018, even though it is in no way specific to the management of myxoedema coma.
  • Establish an airway if this is needed
  • Maintain normoxia and normocapnea with the ventilator
  • Maintain normotension to support organ system perfusion, with a catecholamine infusion
  • Correct the Na⁺ deficit - consider using water restriction alone.
  • Correct hypoglycaemia
  • Correct hypothermia with warming blanket