Euthyroid sick syndrome overview
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief:
Overview
Euthyroid sick syndrome is a thyroid hormone disorder where the levels of T3 (triiodothyronine) and/or T4 (thyroxine) are at unusual levels, in the setting of a nonthyroidal illness. Thyroid hormones play a major role in the metabolism, growth and maturation of the human body. Euthyroid sick syndrome is seen in conditions of starvation and critical illness such as sepsis, surgery, severe trauma, burns, metabolic disorders, bone marrow transplantation, and malignancy. During these stress conditions, there occurs hypermetabolism, increased energy expenditure, hyperglycemia, and muscle loss. It is speculated, that the body in order to contain this hypermetabolism induces some degree of hypothyroidism by inhibiting deiodination of T4 to T3 by the enzyme 5’-monodeiodinase. This is an adaptive process by which the body prevents further muscle and calorie loss. Euthyroid sick syndrome presents with low serum T3. Depending upon the severity and duration of the stress inducing condition, the thyroid-stimulating hormone(TSH), thyroxine (T4), and free T4 (FT4) are affected in variable proportions.[1][2][3]
Historical Perspective
Classification
Pathophysiology
Euthyroid sick syndrome is not a primary thyroid disorder but instead results from changes induced by the nonthyroidal illness. The cause of euthyroid sick syndrome is multifactorial. It is thought that euthyroid sick syndrome is the result of severe illness and inflammation. During these stress conditions, there occurs hypermetabolism, increased energy expenditure, hyperglycemia, and muscle loss. It is speculated, that the body in order to contain this hypermetabolism induces some degree of hypothyroidism by inhibiting deiodination of T4 to T3 by the enzyme 5’-monodeiodinase. This is an adaptive process by which the body prevents further muscle and calorie loss. Inflammation leads to increased production of cytokines that severely affect genes involved in the production and release of T4 and T3. There is also downregulation of TRH and TSH release from the hypothalamus and pituitary gland respectively. It may be signalled by a decrease in leptin caused by malnutrition. On gross pathology, euthyroid sick syndrome does not appear to be dysfunctional. On microscopic histopathological analysis, euthyroid sick syndrome presents with normal thyroid histology.
Causes
Differentiating Euthyroid sick syndrome from Other Diseases
Euthyroid sick syndrome must be differentiated from other causes of hypothyroidism on the basis of clinical features and laboratory findings. In euthyroid sick syndrome, serum T3 is decreased more than T4, the T3RU (T3 resin uptake) is high, and TSH is normal or mildly decreased. In primary hypothyroidism, serum T4 is decreased more than T3, the T3RU (T3 resin uptake) is low, and TSH is increased.
Epidemiology and Demographics
Risk Factors
Screening
Natural History, Complications, and Prognosis
Diagnosis
Diagnostic Criteria
History and Symptoms
Physical Examination
Laboratory Findings
Electrocardiogram
X-ray
CT scan
MRI
Ultrasound
Other Imaging Findings
Other Diagnostic Studies
Treatment
Medical Therapy
Surgery
Primary Prevention
Secondary Prevention
References
- ↑ Plank LD, Connolly AB, Hill GL (1998). "Sequential changes in the metabolic response in severely septic patients during the first 23 days after the onset of peritonitis". Ann. Surg. 228 (2): 146–58. PMC 1191454. PMID 9712558.
- ↑ Economidou F, Douka E, Tzanela M, Nanas S, Kotanidou A (2011). "Thyroid function during critical illness". Hormones (Athens). 10 (2): 117–24. PMID 21724536.
- ↑ Harris AR, Fang SL, Vagenakis AG, Braverman LE (1978). "Effect of starvation, nutriment replacement, and hypothyroidism on in vitro hepatic T4 to T3 conversion in the rat". Metab. Clin. Exp. 27 (11): 1680–90. PMID 30020.