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Introduction: Oxidative stress has been proposed as one of the factors concurring in the pathophysiology of autoimmune thyroid diseases. Reactive oxygen species are the main expression of oxidative stress in biological systems, and their production can overcome antioxidant defenses ultimately leading to cell damage, apoptosis, and death. The present review was aimed at describing the state of the art of the relationships between oxidative stress and autoimmune thyroiditis. The most used biomarkers of oxidative stress and their correlation with thyroid function are reported. Evidence acquisition: We conducted a search of the literature in the English language starting from 2000, using the following search terms: "Hashimoto thyroiditis," "autoimmune thyroiditis," "hypothyroidism," "hyperthyroidism," "oxidative stress," "oxidants," "antioxidant," "advanced glycation end products." Both clinical studies and animal models were evaluated. Evidence synthesis: Data form clinical studies clearly indicate that the balance between oxidants and antioxidants is shifted towards the oxidative side in patients with autoimmune thyroiditis, suggesting that oxidative stress may be a key event in the pathophysiology of the disease, irrespective of thyroid function. Studies in animal models, such as the NOD.H2h4 mouse, confirm that thyroidal accumulation of ROS plays a role in the initiation and progression of autoimmune thyroiditis. Conclusions: Oxidant/antioxidant imbalance represent a key feature of thyroid autoimmunity. Oxidative stress parameters could be used as biochemical markers of chronic inflammation, to better predict the disease evolution along its natural history. Dietary habits and antioxidant supplements may provide protection from autoimmunity, opening new perspectives in the development of more tailored therapies.

The endocrine system is interested by several autoimmune diseases, characterized by different impact and severity, according to the organs involved. Autoimmune thyroid disorders (i.e. Hashimoto's thyroiditis and Graves' disease) and type 1 diabetes mellitus are the most common autoimmune endocrine disorders, while hypophysitis, adrenalitis (90% of cases of primary hypocortisolism or Addison's disease), POF and hypoparathyroidism represent quite rare conditions. Autoimmune endocrine diseases can also coexist in the same individuals and cluster in families. Some of these associations are nosologically codified in the so-called autoimmune polyglandular syndromes, but autoimmune endocrinopathies can also be accompanied by other non-endocrine autoimmune disorders (i.e. connective tissue, skin or gastrointestinal diseases). Pathophysiology generally results from a complex interplay among genetic predisposition and environmental/endogenous factors. In the diagnostic process, measurement of organ-specific autoantibodies, both with a causative role or as an epiphenomenon, is often fundamental and integrates the assessment of hormone axes and the targeted imaging studies.