Thyroid hormone resistance

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.

Causes
The most common cause of the syndrome are mutations of the β (beta) form 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.

Incidence
Thyroid hormone resistance syndrome is rare, incidence is variously quotes as 1 in 50,000 or 1 in 40,000 live births.

Presentation
The syndrome can present with variable symptoms, even between members of the same family harboring the same mutation. Typically most or all tissues are resistant to thyroid hormone, so despite raised measures of serum thyroid hormone the individual may appear euthyroid (have no symptoms of over- or underactivity of the thyroid gland). The most common symptoms are goiter and tachycardia. It has also been linked to some cases of attention deficit hyperactivity disorder (ADHD), although the majority of people with that diagnosis have no thyroid problems.

An association with depression has been proposed.

Diagnosis
The characteristic blood test results for this disorder can also be found in other disorders (for example TSH-oma (pituitary adenoma), or other pituitary disorders). The diagnosis may involve identifying a mutation of the thyroid receptor, which is present in approximately 85% of cases.

Yet, since discovery of resistance to thyroid hormones in the absence of thyroid hormone receptor beta mutations, lack of a mutation in a patient does not rule out resistance.

Terminology
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.

Claims of cause of fibromyalgia and chronic fatigue syndromes
Recent evidence has come to light through the works of Dr. Samuel Refetoff, Dr. Roy Weiss and Dr. John C. Lowe, that thyroid hormone resistance is far more common than once suspected. Refetoff has linked thyroid hormone resistance with a variety of other diseases that many times mask the real problem because thyroid hormone resistance is not always detectable by blood work. Some forms of hormone resistance affect the conversion of T4 thyroid hormone to T3 and result in insufficient hormone reaching bodily tissues the at the cellular level. This type of conversion malfunction is not always detectable by blood tests which tell us how much hormone is circulating in the blood not what is reaching the tissues. Sometimes a reverse T3 will show that there is a conversion malfunction but in only one subset of the many groups of conversion malfunctions. What modern doctors are realizing is that a person may have a sever thyroid insufficiency without the blood tests indicating this. Dr. Lowe believes through extensive research, that fibromyalgia and chronic fatigue syndrome are frequently misdiagnoses of partial resistance to thyroid hormone. He and Dr. Dennis Wilson use T3 therapy with drugs such as Cytomel and compounded T3 in patients who may even have normal thyroid blood tests. The result is that these patients improve or even recover completely while their blood tests may indicate they are taking too much thyroid hormone. Since they must take more thyroid hormone than others, the result is an excess of thyroid hormone floating around in the blood stream, however what reaches the tissues is usually far less, in fact a normal amount. This shocks doctors who do not understand thyroid hormone resistance. Such doctors are under a mistaken belief that if the blood tests show thyrotoxicity (too much thyroid hormone) then it must be true, even though their patients cannot recover or feel well without this high dose. Doctors like Refetoff, Lowe, Berndtson, Wilson and Papernick have come to discover, that to bring their patients health and free them from their terrible symptoms, they must prescribe these large doses. Interestingly, aside from the blood test results, thyroid hormone resistance patients do not experience the symptoms of thyrotoxicity such as diahhreah, hives, hair loss, heart palpitations and nervousness and in fact do experience the symptoms of hypothyroidism if they are not medicated with these high doses of T3.

Dr. Refetoff has also noted that there are many cases that present thyroid hormone resistance without the genetic mutation. Nobody knows what causes thyroid hormone resistance in these patients but doctors have discussed the possility of environmental toxicities, stealth viruses, mutated bacteria, systemic fugal infection and others. Dr. Marshall has invented a protocol for Sarcoidosis and autoimmune disease that is proving to free many thyroid hormone resistant patients from their symptoms and their large doses of medication. His research would indicate that there is an autoimmune manlfunction causing thyroid hormone resistance.

However, thyroid hormone resistance is suspected to occur in 1%-3% of the entire female population if Dr. Lowe is correct in his belief that Fibromyalgia is thyroid hormone resistance. Dr. Refetoff believes that many people with ADD have thyroid hormone resistance which would cover another large chunck of the population. In fact, it is unknown how many people have it, but we now know that it is not a rare disorder as once was believed.

The other symtoms that indicate a person may have thyroid hormone resistance include but are not limited to: low body temperature, blood pressure problems, chronic fatigue, constipation, fibromyalgia or widespread pain, weight gain, memory problems, cognitive dysfunction, asthma or allergies, and all other symptoms commonly associated with either Hashimoto's thyroiditis and/or regula hypothyroidism, and/or regular hyperthyroidism. The symptoms of this illness are many but the only way to really know if you have it, is to work with a doctor on a therapeutic trial of the thyroid hormone therapy. If a person cannot achieve homoeostasis without large doses of T3 or T4, then she/he may have thyroid hormone resistance. Dr. Refetoff has studied people who needed 1000mcg of T4 and 500mcg of T3 before feeling well. These are doses that would kill a normal person and yet for those with thyroid hormone resistance, living without these supraphysiologic doses feels like death.

Proposed treatment
Treatment varies vastly from person to person but what is common to all are the high doses of thyroid hormone necessary before a patient feels well. First, treatments can be desiccated or synthetic. Then, they can be either T3, T4 or combination T3/T4 drugs. Dr. Lowe has published the most extensive guidelines for properly medicating those with thyroid hormone resistance. Also note, that not all tissues absorb thyroid hormone at the same rate. The heart for example, may absorb at a higher rate than the lungs and muscles. This means, patients may need other drugs to supplement this difference in absorption rate. For many, this includes a beta blocker to reduce stimulation on the heart and allow for a higher hormone dose to better alleviate muscle or lung resistance. It is a balancing act that can only be adjusted by your symptoms and medical tests.

Desiccated thyroid is made from pig hormones. It is usually a cheaper drug and it is considered "natural." An additional note is that according to Dr. Lowe, many people with thyroid hormone resistance cannot assimilate desiccated thyroid drugs like naturthroid and armour. This has to do with the extra conversion the body must go through to assimilate desiccated thyroid. This group of people will do far better on synthetic thyroid drugs. Furthermore, desiccated thyroid is a combination T3/T4 drug and does not allow for the fine tuning involved if a patient's optimal ratio is different than that compounded into the drug. For example, armour thyroid has a ration of T4/T3 of 4/1. But people with thyroid hormone resistance may not improve without a ratio of 2/1 or even 1/1. This cannot be achieved with desiccated thyroid alone.

Many patients recover with only T3 or only T4. These patients will take drugs like synthroid or levoxy for T4 and cytomel or time released compounded T3 for the T3. Those on T3 drugs who find the drugs too stimulating can switch to a time released mechanism to prolong the benefits of the T3 drug which is typically out of the system in 2-4 hours. With a time released drug it can stay in the system longer and will reduce the crash when the drug runs out. T4 stays in the system longer but it does not always convert to active usable T3. For this reason, some people do better on combination T4 and T3 therapy. Thyrolar is a combination synthetic drug that many prefer. However, if a patient does not feel optimal on thyrolar it may be that he/she needs to independently adjust the T3 and T4 to a different ration than that compounded into the drug.

Some people take their thyroid dose all at one time in the morning. Others must divide the dose into two or three daily doses.