Acute infection sets the stage for potential long-COVID. At the time of initial infection, multiple studies have reported a decline in total-T3 levels with or without changes in thyroid stimulating hormone (TSH). In patients without TSH fluctuations these researchers hypothesized a direct cytotoxic effect of the virus on thyroid tissue, resulting in euthyroid sick syndrome. They also found that those that experienced this had more severe systemic inflammation. Secondarily, in those that did have changes in TSH levels, scientists hypothesized that the virus influenced the hypothalamic-pituitary-thyroid (HPA) axis, resulting in lower TSH and higher interleukin-6 (IL-6) levels and therefore a more robust inflammatory response (1). Whether this is strictly an acute reaction to the virus or something that results in chronic issues depends on numerous factors, with some individuals experiencing more long-term thyroid issues.

Autoimmunity is another consideration when investigating possible thyroid-related outcomes. Autoimmune conditions have been cited by multiple studies, with thyroid specific conditions reported by only a few. Cabuk et al cited the potential of subacute thyroiditis, which is associated not only with the COVID virus, but other viral infections including measles, mumps, adenovirus, etc. Thankfully, this condition tends to be self-limiting and does resolve over time (1).

When it comes to longer term thyroid issues that can be associated with long-COVID, the good news is almost all fluctuations during the acute infection do resolve spontaneously, making chronic issues rather rare. That being said, researchers have found incidental positivity in anti-thyroid-peroxidase (anti-TPO) antibodies. These antibodies are associated with both Hashimoto’s Thyroiditis, a type of hypothyroidism, and Graves’ Disease, a type of hyperthyroidism. Interestingly enough however, those with this incidental finding were found to have higher rates of symptom resolution post infection, therefore indicating a possible protective effect when it comes to developing long-COVID (2).