A somewhat related “psychosis”-story from one of the self-help boards, told by a young woman:
She had been hyperthyroid as a teenager and had a total thyroidectomy (thyroid removal). Such patients then have to take levothyroxine (T4) for life, as without a thyroid they’re no longer able to produce the hormone. The doctors told her she had to take the T4, but they didn’t tell her what would happen if she didn’t. So, eventually, she just stopped (patients do crazy shit quite frequently). The thing with T4 is that it has a very long biological half-life, about 9 days if you’re hypothyroid. So nothing bad happened immediately. After several weeks, however, she started hallucinating and feeling really bad and went to the ER. This state is referred to as myxedema.
Part of any emergent psychiatric evaluation is a thyroid function test, because thyroid dysfunction can cause some very extreme psychiatric symptoms. There are three relevant thyroid-related hormones you can test - TSH (thyroid stimulating hormone, the “gas pedal” for the thyroid, which is produced by the pituitary gland), T4* (produced by the thyroid) and T3 (the active thyroid hormone, which is mostly converted from T4). Oftentimes, only TSH is tested. If TSH is high, there’s usually too little T4, if it’s low, there’s too much. To save money, you test only TSH and then you go on to test T4 if there’s an issue with TSH.
So that’s what they did. Unfortunately, the young woman didn’t only not have a thyroid, she also had some kind of damage to the pituitary. Under normal circumstances, given the fact that no T4 was being produced, her TSH would have been sky-high. But in this case, it was 2, which looked perfectly normal.
So they committed her to a mental health facility. It took quite a while (several weeks as I recall) until someone ran an fT4 test and figured it out. Her suffering must have been unimaginable.
*for most purposes, “free” T4 (fT4) and “free” T3 (fT3) are tested. This is the fraction of T4 and T3 that’s not bound to proteins.