Severe hypothyroidism comes up often as a differential for various things, but only Question 11 from the second paper of 2002 and Question 14 from the second paper of 2021 address it directly (diagnosis, features, management). The hypothyroidism considered in this chapter lays somewhere between the mild "sick euthyroid" syndrome and frank myxoedema. Myxoedema coma comes up much more often in the exam, and has been allocated to its own chapter.
An excellent article is available, which treats this topic with the detail it deserves. This detail has been distilled and concentrated in this table, to simplify revision:
One can summarise these by saying that everything goes slower.
There's yet more findings which are not listed here. What you see here are findings associated with severe hypothyroidism, of the sort that might require hospitalisation. In addition to this, there are features listed in the myxoedema coma chapter, which represent the next level of clinical severity in the spectrum. Thoseinclude ECG changes, cardiogenic shock, and so forth.
Well, one could do no better than to replace the missing hormone. Its not clever, but it is the right solution. In myxoedema coma, one may wish to replace it intravenously. A dose of 50 to 200mcg is usually enough. One traces the efficacy of one's management by observing the decrease in TSH (which should be elevated in "proper" hypothyroidism, and which will fall to normal levels as thyroid function is restored). The addition of corticosteroids into the mix tends to be advocated because until test results are available, one is never sure whether one is dealing with some sort of hypoadrenal syndrome.
The literature for the management of severe hypothyroism and myxoedema coma is somewhat scant on evidence. For example, one of the best articles on this topic is Ringel (2001), where one could literally go for some pages of excellent practical suggestions without encountering a single supporting reference. Clearly a lot of what we do in the ICU for this condition is based on expert opinion, theoretical physiology and personal experience. With that caveat: