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.
Euthyroid sick syndrome pathophysiology
Euthyroid sick syndrome risk factors
Cushing's syndrome pathophysiology
Acromegaly pathophysiology
Euthyroid sick syndrome epidemiology and demographics
Euthyroid sick syndrome laboratory findings
Euthyroid sick syndrome causes
Acromegaly risk factors