Thyroid hormone resistance
From Wikipedia, the free encyclopedia
| Thyroid hormone resistance | |
|---|---|
| Classification and external resources | |
| ICD-10 | E07. |
| ICD-9 | 246.8 |
| OMIM | 274300 188570 |
| DiseasesDB | 31913 |
| MeSH | D018382 |
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.
Contents |
[edit] Causes
The most common cause of the syndrome are mutations of the β (beta) form (THRB) 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.[1]
[edit] Incidence
Thyroid hormone resistance syndrome is rare, incidence is variously quoted as 1 in 50,000 or 1 in 40,000 live births.
[edit] Presentation
The syndrome can present with variable symptoms, even between members of the same family harboring the same mutation.[2] 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.[3]
An association with depression has been proposed.[4]
[edit] 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.[5]
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.[6]
[edit] 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.
[edit] 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.
[edit] References
- ^ Refetoff S, Dumitrescu AM (2007). "Syndromes of reduced sensitivity to thyroid hormone: genetic defects in hormone receptors, cell transporters and deiodination". Best Pract. Res. Clin. Endocrinol. Metab. 21 (2): 277–305. doi:. PMID 17574009. http://linkinghub.elsevier.com/retrieve/pii/S1521-690X(07)00026-7.
- ^ Refetoff S, DeWind LT, DeGroot LJ (1967). "Familial syndrome combining deaf-mutism, stuppled epiphyses, goiter and abnormally high PBI: possible target organ refractoriness to thyroid hormone". J. Clin. Endocrinol. Metab. 27 (2): 279–94. PMID 4163616.
- ^ Hauser P, Zametkin AJ, Martinez P, et al. (1993). "Attention deficit-hyperactivity disorder in people with generalized resistance to thyroid hormone". N. Engl. J. Med. 328 (14): 997–1001. doi:. PMID 8450877.
- ^ Fardella CE, Artigas RA, Gloger S, et al. (2007). "Refractory depression in a patient with peripheral resistance to thyroid hormone (RTH) and the effect of triiodothyronine treatment". Endocrine 31 (3): 272–8. doi:. PMID 17906375. http://www.humanapress.com/ArticleDetail.pasp?issn=0969-711X&acode=ENDO:31:3:272.
- ^ Bottcher Y, Paufler T, Stehr T, Bertschat FL, Paschke R, Koch CA (2007). "Thyroid hormone resistance without mutations in thyroid hormone receptor beta". Med. Sci. Monit. 13 (6): CS67–70. PMID 17534237.
- ^ Tjørve E, Tjørve KM, Olsen JO, Senum R, Oftebro H (2007). "On commonness and rarity of thyroid hormone resistance: a discussion based on mechanisms of reduced sensitivity in peripheral tissues". Med. Hypotheses 69 (4): 913–21. doi:. PMID 17383828. http://linkinghub.elsevier.com/retrieve/pii/S0306-9877(07)00128-4.
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