Euthyroid sick syndrome pathophysiology

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Akshun Kalia M.B.B.S.[2]


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, hypermetabolism occur, that lead to increased energy expenditure, hyperglycemia, and muscle loss. It is speculated, that the body induces some degree of hypothyroidism by inhibiting deiodination of T4 to T3 by the enzyme 5’-monodeiodinase, in order to contain the hypermetabolism. This is an adaptive process by which the body prevents further muscle and calorie loss. Inflammation leads to increased production of cytokines that severely affects 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. This downregulation 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.




Pathogenesis of euthyroid sick syndrome include mutation in LEP gene.

Associated Conditions

Euthyroid sick syndrome is seen with starvation and severe illness such as:[14][15]

Gross Pathology

In euthyroid sick syndrome the thyroid gland appears normal on gross pathology.

Microscopic Pathology

On microscopic histopathological analysis, euthyroid sick syndrome presents with normal thyroid histology.

Histology of normal thyroid gland. 1. Colloid 2. Cellular Epithelium Arrow: C-Cell (Source - By M-J-G (Own work) [CC BY-SA 4.0, via Wikimedia Commons)


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  6. Bartalena, L; Bogazzi, F; Brogioni, S; Grasso, L; Martino, E (1998). "Role of cytokines in the pathogenesis of the euthyroid sick syndrome". European Journal of Endocrinology. 138 (6): 603–614. doi:10.1530/eje.0.1380603. ISSN 0804-4643.
  7. Légrádi G, Emerson CH, Ahima RS, Flier JS, Lechan RM (1997). "Leptin prevents fasting-induced suppression of prothyrotropin-releasing hormone messenger ribonucleic acid in neurons of the hypothalamic paraventricular nucleus". Endocrinology. 138 (6): 2569–76. doi:10.1210/endo.138.6.5209. PMID 9165050.
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  9. Froguel, Philippe; Clément, Karine; Vaisse, Christian; Lahlou, Najiba; Cabrol, Sylvie; Pelloux, Veronique; Cassuto, Dominique; Gourmelen, Micheline; Dina, Christian; Chambaz, Jean; Lacorte, Jean-Marc; Basdevant, Arnaud; Bougnères, Pierre; Lebouc, Yves; Guy-Grand, Bernard (1998). "A mutation in the human leptin receptor gene causes obesity and pituitary dysfunction". Nature. 392 (6674): 398–401. doi:10.1038/32911. ISSN 0028-0836.
  10. Lechan RM, Fekete C (2005). "Role of thyroid hormone deiodination in the hypothalamus". Thyroid. 15 (8): 883–97. doi:10.1089/thy.2005.15.883. PMID 16131331.
  11. Abo-Zenah HA, Shoeb SA, Sabry AA, Ismail HA (2008). "Relating circulating thyroid hormone concentrations to serum interleukins-6 and -10 in association with non-thyroidal illnesses including chronic renal insufficiency". BMC Endocr Disord. 8: 1. doi:10.1186/1472-6823-8-1. PMC 2254394. PMID 18211669.
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  14. Silva MH, Araujo MC, Diniz EM, Ceccon ME, Carvalho WB (2015). "Nonthyroidal illnesses syndrome in full-term newborns with sepsis". Arch Endocrinol Metab. 59 (6): 528–34. doi:10.1590/2359-3997000000111. PMID 26677087.
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