What is the most severe form of hypothyroidism called?

The most severe form of hypothyroidism is referred to as myxedema. This condition results from prolonged untreated hypothyroidism and can lead to significant metabolic slow down and various systemic complications. In myxedema, patients may exhibit symptoms such as severe lethargy, multiple organ dysfunction, hypothermia, and can even progress to a myxedema coma, which is a life-threatening state requiring immediate medical intervention.

Cretinism, another form of hypothyroidism, typically refers to congenital hypothyroidism and results in physical and developmental delays if not treated at an early age, but it is not classified as the most severe form in adults. Grave's disease is actually an autoimmune disorder that leads to hyperthyroidism, characterized by excessive thyroid hormone production, which contrasts with the low levels seen in hypothyroidism. Exophthalmos refers to the protrusion of the eyes, which can be a symptom of hyperthyroid conditions like Grave's disease, rather than hypothyroidism itself. Therefore, myxedema stands out as the most severe manifestation of an underactive thyroid.