Long-Term Thyroid Complications Post-COVID-19: A Systematic Review

Coronavirus disease 2019 (COVID-19) is increasingly shown to be a multisystem disorder with long-term complications, including endocrine system complications. The thyroid gland is also susceptible, as it contains ACE2 receptors, making it exposed to both direct viral damage and autoimmune-mediated dysfunction. Recent reports document the various thyroid complications that persist well after the acute infection phase. This systematic review investigates the long-term thyroid complications in individuals with a history of SARS-CoV-2 infection. A comprehensive literature search across several databases was conducted. Eligible studies reported new onset long-term thyroid complications occurring post-COVID-19 infection. Abstract and full-text screening as well as data extraction and quality assessment was performed by two independent reviewers. Only 28 studies met our inclusion criteria, reporting 419 patients from 18 countries. These studies included case reports, case series, cohort, and cross-sectional studies. Reported thyroid disorders included subacute thyroiditis, thyrotoxicosis, hyperthyroidism (including Graves' disease), isolated high T3/T4, hypothyroidism, central hypothyroidism, and non-thyroidal illness syndrome (NTIS). While many of these eventually resolved, a significant portion persisted or recurred, especially autoimmune thyroiditis. COVID-19 is associated with a range of long-term thyroid complications. Although some cases are temporary, others last, especially autoimmune thyroid disorders. Proposed mechanisms include direct viral cytotoxicity, cytokine-mediated Hypothalamic-Pituitary-Thyroid (HPT) axis suppression, post-viral autoimmunity, vascular injury, and neuroendocrine disruption. Routine thyroid function monitoring in COVID-19 survivors, particularly those with severe disease or persistent symptoms is recommended, and larger prospective studies are needed to better understand incidence and outcomes.