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).
D. Misdiagnosis and Diagnosis
D.1. Misdiagnosis
1. Hyperthyroidism
There is a report of an isolated case of RTH initially misdiagnosed as
hyperthyroidism, and detail the investigations which ultimately led to
the correct diagnosis(23).
2. Falsely diagnnosis
There is a report of a 63-year-old woman was referred because of
suspected SITSH. Laboratory tests showed a normal TSH (0.52 μIU/L;
normal range: 0.5-5.0) measured by sandwich Elecsys, and elevated FT4
(3.8 ng/dL; normal range: 0.9-1.6) and FT3 (7.6 pg/mL; normal range:
2.3-4.0), determined by competitive Elecsys. To exclude possible assay
interference, aliquots of the original samples were retested using a
different method (ADVIA Centaur), which showed normal FT4 and FT3
levels. Eight hormone levels, other than thyroid function tests measured
by competitive or sandwich Elecsys, were higher or lower than levels
determined by an alternative analysis. Subsequent examinations,
including gel filtration chromatography, suggested interference by
substances against ruthenium, which reduced the excitation of ruthenium,
and resulted in erroneous results(24). Other suggested that patients
with TSH-secreting pituitary tumors(TSHoma) also manifest SITSH. Thus,
the differential diagnosis of RTH vs. TSHoma is sometimes difficult and
challenging. In this review article, the etiology of RTH and diagnostic
approach for SITSH are explained and an algorithm for differential
diagnosis of RTH vs. TSHoma is proposed(25).
3. Coexistence of mutation genes
There is a report of the coexistence of THRB and TBG gene mutations in
the same individual (mother of the proband), whereas other affected
family members had only 1 of the 2 genes mutated. The case illustrates
the difficulty that might be encountered in the interpretation of
thyroid function tests when different genetic defects affecting thyroid
function coexist(26).
4. Grave’s disease
RTH is often misdiagnosed as Graves’ disease. However, these disorders
can coexist, and the concurrent presence of both disorders in a patient
can present diagnostic challenges. A previous report of a patient with
Graves’ disease associated with RTH was published before gene sequencing
could be used to confirm diagnosis of RTH. There is a report of a
patient with Graves’ disease and concurrent RTH that was confirmed by
gene sequencing, showing a mutation in the thyroid hormone receptor beta
gene(27).
D.2. Diagnosis
If you are experience certain symptoms of the above and your doctor
suspects that you have developed acute thyroiditis, after recording the
past and present history and completing a physical exam, the tests which
your doctor orders may include
1. Urinary test
Urinary cortisol metabolites are altered both quantitatively and
qualitatively in thyroid dysfunction. According to the study by the
Showa University, the ratio of the urinary concentrations of cortisol
metabolites, THE/THF, appears to be a good marker for peripheral thyroid
hormone resistance(28).
2. Blood test
Unfortunately, the blood test results of the disorder can also be found
in other disorders such as TSH-oma (pituitary adenoma), or other
pituitary disorders. According to the study by the Nagoya University,
almost all patients with RTH manifest unsuppressed thyrotropin (TSH)
despite elevated free-T4 and free-T3 levels. This abnormal finding in
the thyroid function test is termed “syndrome of inappropriate secretion
of TSH” (SITSH) or “central hyperthyroidism”. Patients with
TSH-secreting pituitary tumors(TSHoma) also manifest SITSH. Thus, the
differential diagnosis of RTH vs. TSH-oma is sometimes difficult and
challenging(29)
3. Identifying a mutation of the thyroid receptor
Resistance to thyroid hormone (RTH) is a rare condition usually
diagnosed in patients with classic thyroid function tests (TFTs) of
elevated thyroid hormone levels with nonsuppressed TSH. According to the
study by the, At least six major steps are required for secreted
thyroid hormone (TH) to exert its action on target tissues. Mutations
interfering with three of these steps have been so far identified. The
first recognized defect, which causes resistance to TH, involves the TH
receptor β gene and has been given the acronym RTH(30).
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Sources
(23) http://www.ncbi.nlm.nih.gov/pubmed/16445164
(24) http://www.ncbi.nlm.nih.gov/pubmed/22673200
(25) http://www.ncbi.nlm.nih.gov/pubmed/23214067
(26) http://www.ncbi.nlm.nih.gov/pubmed/23633200
(27) http://www.ncbi.nlm.nih.gov/pubmed/20151830
(28) http://www.ncbi.nlm.nih.gov/pubmed/8257864
(29) http://www.ncbi.nlm.nih.gov/pubmed/23214067
(30) http://www.bprcem.com/article/S1521-690X%2807%2900026-7/abstract
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