Thyroid hormone resistance describes a rare syndrome where the thyroid hormone levels are elevated but the thyroid stimulating hormone (TSH) level is not suppressed, or not completely suppressed as would be expected.So there is a one clearly defined disease called "Thyroid Hormone Resistance", which is caused by genetic mutation and is relatively rare.
The most common cause of the syndrome are mutations of the β (beta) form (THRB gene) of the thyroid hormone receptor, of which over 100 different mutations have been documented. Mutations in MCT8 and SECISBP2 have also been associated with this condition.
Thyroid hormone resistance syndrome is rare, incidence is variously quoted as 1 in 50,000 or 1 in 40,000 live births.
Sometimes the phrase thyroid hormone resistance is used to identify cases where patients with autoimmune thyroid disorders respond poorly to normal doses of replacement thyroid hormone. This is thought to occur where patients have developed antibodies to thyroid hormones. Antibodies to thyroid hormones quite commonly occur in such disorders, and may interfere with the normal clinical assays used in monitoring such disorders, and in unusual cases may have further independent clinical significance.
And then there is the fuzzy quack "phrase" of some supposed thyroid hormone resistance, that gets thrown around when patients respond "poorly" to thyroid hormone. From the description by Emily Deans (here and here), it would seem like patients who don't respond to thyroid-hormes may actually have health problems that aren't caused by thyroid-hormone resistance in the first place…