Friday, 29 November 2013

Thyroid hormone resistance syndrome – The Complications and diseases associated to

Thyroid disease is defined as a condition of malfunction of thyroid. Hyperthyroidism is a condition in which the thyroid gland is over active and produces too much thyroid hormones. Hypothyroidism is a condition in which the thyroid gland is under active and produces very little thyroid hormones. Thyroid cancer is defined as condition in which the cells in the thyroid gland have become cancerous.
Thyroid hormone resistance syndrome
Thyroid hormone resistance syndrome is defined as a condition of which affected individuals have elevated serum thyroid hormone levels and inappropriately normal or elevated thyroid-stimulating hormone (TSH) but are usually clinically euthyroid and require no treatment. Selective pituitary resistance to thyroid hormone (PRTH) is characterized by resistance in the pituitary gland but not in peripheral tissues(a).
C. Complications and diseases associated to Thyroid hormone resistance
C.1. Complications
1. Growth retardation/short stature and skeletal dysplasia
There is a report of a first human cases (female, age 6 y; father and daughter, ages 47 and 11 y, respectively) with growth retardation/short stature, skeletal dysplasia, constipation, and defective thyroid receptor α (TRα)(14).
2. Thyroxine excess and inappropriate TSH secretion
Resistance to thyroid hormone (RTH) is an uncommon inherited cause of hyperthyroxinemia with inappropriate TSH secretion, according to the study by the University of Cambridge, Addenbrooke’s Hospital, United Kingdom(15).
3. Cardiovascular risk
RTH patients show evidence in this study of increased augmentation index consistent with an increase in arterial stiffness compared with euthyroid controls. They also demonstrate elevated LDL-cholesterol levels. Both these measures may lead to increased cardiovascular risk(16).
C.2. Diseases associated to Thyroid hormone resistance
1. Differentiated thyroid cancer (DTC)
There are reports of four unusual cases of DTC associated with TSHoma (2 cases), RTH (1 case), and an elevated TSH of unknown etiology (1 case)(17).
2. A pituitary tumor
There is a report of a woman in whom the standard evaluation for inappropriate TSH secretion was insufficient to distinguish these entities. The patient had a low-normal TRH stimulation test and an unmeasurable alpha-glycoprotein subunit level; however, a pituitary magnetic resonance imaging (MRI) revealed an adenoma. More testing using a T3 suppression test supported a RTH diagnosis and a R438H mutation was found in the TR-beta gene. To our knowledge, this represents the first report of an apparently incidental pituitary adenoma in the setting of documented resistance to thyroid hormone. As such, it raises the question of whether RTH predisposes to pituitary hyperplasia and adenoma. development(18).
3. Papillary thyroid carcinoma
There is an association of thyroid hormone resistance syndrome and papillary thyroid carcinoma(19).
4. Immune thrombocytopenic purpura (ITP)
There is a report of a 9-year-old girl presented with ITP and features of hypothyroidism in the form of goiter and growth retardation. She was subsequently found to have RTH. High-dose thyroid hormone replacement was required to overcome the resistance that not only ameliorated the features of hypothyroidism but also brought an apparent remission of ITP(20).
5. Postpartum thyroiditis
there is a repopt of a report of a unique case of a woman affected by RTH, due to a novel mutation V283A in THRB, who experienced PPT with a severe thyrotoxic phase after both her pregnancies. The association between RTH and PPT has never been reported in the literature. In particular, the marked suppression of TSH occurring when levels of TH are particularly elevated is not a frequent condition during RTH(21).
6. Chronic thyroiditis
There is a report of the five-year medical history of a Japanese woman and her father with RTH and coincidental chronic thyroiditis(22).
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