Myxedema psychosis, more colloquially known as myxedema madness, is a relatively uncommon consequence of hypothyroidism, such as in Hashimoto's thyroiditis or in patients who have had the thyroid surgically removed and are not taking thyroxine. A chronically under-active thyroid can lead to slowly progressive dementia, delirium, and in extreme cases to hallucinations, coma, or psychosis, particularly in the elderly. It was first recognized by Dr Richard Asher of London in 1949.
Treatment is via the standard treatment for hypothyroidism with thyroxine replacement. Oral T4, or in especially acute cases liothyronine, a sodium salt of T3. Hormone replacement in these patients usually reverses the psychotic symptoms, but may not help with cognitive deficits caused by changes in metabolic activity in the CNS.
The "myxedema" part of the name simply refers to the non-pitting edema common to hypothyroidism.