Cause-and-effect relationship between thyroid and liver diseases

Abstract

Thyroid gland (TG) and the liver are in a complex relationship in both physiological and pathological conditions. Thyroid hormones accelerate metabolic processes, intensify the synthesis of proteins and vitamins, play an important role in the development and differentiation of all cells, including hepatocytes. In addition to the central role in the deiodination of thyroid hormones with the formation of their more active and inactivated forms, the liver also carries out their transport. Dysfunction of TG can lead to changes in liver function, and in liver diseases, abnormalities in the metabolism of thyroid hormones can occur. Most often, liver pathology in diseases of TG is manifested by an increase in the serum activity of enzymes of cytolysis and/or cholestasis. Changes in liver function tests are often observed in patients with thyrotoxicosis. They are based on oxidative stress or cholestasis. The increased activity of osteoblasts in hyperthyroidism leads to an increase in the bone fraction of alkaline phosphatase, which must be taken into account in the differential diagnosis. Hepatotoxicity of thyreostatic drugs is relatively common, ranging from minimal hepatocellular damage to fulminant liver failure. In the case of hypothyroidism, the pathophysiological mechanisms are mainly represented by lipid metabolism disorders leading to fatty degeneration. It should be remembered that severe hypothyroidism can be manifested by hyperammonemia and edematous-ascitic syndrome, requiring differential diagnosis with liver failure. Treatment of liver pathology in TG diseases includes normalization of thyroid status, and in cases of drug hepatitis – temporary withdrawal of a potentially hepatotoxic drug. The data on the association of hypothyroidism and non-alcoholic fatty liver disease in the aspect of developing new therapies are very interesting.