Prevalence and Evolution of Thyroid Dysfunction in COVID-19: A Retrospective Study

Objective Coronavirus-19 (COVID-19) is known to mainly affect the respiratory system, but it has also been found to impact multiple endocrine systems. Various studies have shown a relationship between thyroid dysfunction and COVID-19 infection. However, there is controversy around thyroid-inflammatory autoimmune conditions contributing to a worse prognosis of COVID-19 infection. The main objective of our single-center retrospective study is to evaluate the prevalence and evolution of thyroid dysfunction in patients with COVID-19 infection. Methods A total of 615 adults with confirmed COVID-19 infection, between March 2020 and December 2023, who had thyroid function tests (TFTs), were included in the study. Patients with pre-existing thyroid disease or on medications affecting thyroid function were excluded. Thyroid dysfunction was defined as any abnormality in TFTs. Statistical analyses were performed using IBM SPSS Statistics for Windows, Version 26 (Released 2018; IBM Corp., Armonk, NY, USA). Differences in continuous variables were assessed using independent sample t-tests, and Pearson's Chi-square tests were used to compare categorical variables. Results The study showed that 84 patients (13.6%) had thyroid dysfunction. The most common abnormalities were non-thyroidal illness syndrome (NTIS, n = 39; 46.4%) and subclinical hypothyroidism (n = 37; 44%), followed by overt hyperthyroidism (n = 6; 7.1%) and overt hypothyroidism (n = 2; 2.3%). The evolution of thyroid dysfunction was followed for about one year by chart review and showed no progression to overt thyroid dysfunction. Conclusion We noted that thyroid dysfunction is not uncommon in patients with COVID-19, with subclinical hypothyroidism and NTIS being the most prevalent findings. These abnormalities are often transient and resolve without progression in most cases. The pathogenesis appears to involve both direct viral effects and systemic inflammatory responses. Given the potential overlap between thyroid dysfunction and long COVID symptoms, selective monitoring of thyroid function is warranted in symptomatic individuals.