Individuals who experience inflammation of the thyroid gland during acute COVID-19 illness may still have subacute thyroiditis months later, even if thyroid function has normalized, new research suggests.
Furthermore, the thyroiditis seems to be different from thyroid inflammation caused by other viruses, said Ilaria Muller, MD, PhD, when presenting her findings March 21 at the virtual ENDO 2021 meeting.
“SARS-CoV-2 seems to have multifactorial action on thyroid function,” said Dr. Muller, of the University of Milan, Fondazione IRCCS Ca’ Granda Ospedale Maggiore Policlinico, Italy.
In July 2020, Dr. Muller and colleagues described patients hospitalized at their institution with severe COVID-19, 15% of whom had thyrotoxicosis due to atypical subacute thyroiditis, compared with just 1% of a comparison group hospitalized in the same subintensive care units during the spring of 2019, as reported by this news organization.
The “atypical” thyroiditis that occurred in the patients with COVID-19 was not associated with neck pain and affected more men than women. Moreover, it was associated with low TSH and free-triiodothyronine (T3) levels, and normal or elevated levels of free-thyroxine (T4), which is a very different presentation to classic nonthyroidal illness syndrome (NTIS) usually seen in critically ill patients, she explained.
Although transient T4 elevations can occur in acute illness, that phenomenon is not associated with low TSH. This newly described scenario appears to be a combination of thyrotoxicosis and NTIS, Dr. Muller and colleagues had speculated last summer.
Follow patients with COVID-19 and thyroid dysfunction for a year
Now, in an assessment of 51 patients 3 months after hospitalization for moderate-to-severe COVID-19 reported by Dr. Muller at ENDO 2021, both inflammatory markers and thyroid function had normalized, yet on imaging, a third of patients still exhibited focal hypoechoic areas suggestive of thyroiditis.
Of those, two-thirds had reduced uptake on thyroid scintigraphy, but few had antithyroid autoantibodies.
“The thyroid dysfunction induced by COVID-19 seems not mediated by autoimmunity. It is important to continue to follow these patients since they might develop thyroid dysfunction during the following months,” Dr. Muller emphasized.
Asked to comment, session moderator Robert W. Lash, MD, the Endocrine Society’s chief professional & clinical affairs officer, told this news organization: “When you’re ICU-level sick, it’s not unusual to have weird thyroid tests. Some viruses cause thyroid problems as well ... What makes this different is that while a lot of thyroid inflammation is caused by antibodies, this was not.”
“It looks like this was [SARS-CoV-2] causing damage to the thyroid gland, which is interesting,” he noted, adding that the thyroid gland expresses high levels of angiotensin-converting enzyme 2 (ACE2) and transmembrane protease serine 2 (TMPRSS2), which allow SARS-CoV-2 to infect human cells.
“This is probably part of that same story,” Dr. Lash said.
For patients who had thyroid abnormalities during acute COVID-19 illness or develop symptoms that might be thyroid-related afterward, he advises: “You should keep an eye on thyroid tests. It just raises your awareness ... You might check their thyroid tests every 6 months for a year.”
Signs of focal thyroiditis despite normalized thyroid function
The 51 patients (33 men and 18 women) hospitalized with moderate-to-severe COVID-19 had no history of thyroid disease and had not been taking thyroid medications, amiodarone, or steroids before baseline TSH was measured.
From baseline to 3 months, TSH rose from 1.2 to 1.6 mIU/L, while serum concentrations of T4, T3, C-reactive protein, and full blood counts had all normalized (all P < 0.01 vs. baseline).
Thyroid ultrasound at 3 months in 49 patients showed signs of focal thyroiditis in 16 (33%).
Among 14 patients of those who further underwent thyroid 99mTc or I123 uptake scans, four (29%) were normal, eight (57%) had focally reduced uptake, and two (14%) had diffusely reduced uptake.
Of the 16 patients with focal thyroiditis, only three were positive for autoantibodies to thyroglobulin (TgAb) or thyroid peroxidase (TPOAb). All were negative for autoantibodies to the TSH receptor.
“Importantly, of the two with diffusely reduced uptake, only one was positive for TPOAb or TgAb,” Dr. Muller noted, adding, “SARS-CoV-2 disease seems to trigger some dysfunction which very likely has complex and multifactorial mechanisms.”
In response to a question about a possible role for biopsies and thyroid cytology, Dr. Muller replied: “That’s definitely the key ... So far we’re just making guesses, so the key will be cytological or histological studies to see what is really going on in the thyroid.”
“What we know is that [unlike] classical thyroiditis that has been described after viral diseases including SARS-CoV-2, these patients have a different scenario ... Probably something is going on within the thyroid with a different mechanism, so surely cytology and histology studies are what we need,” she concluded.
The study was funded by Fondazione IRCCS Ca’ Granda Ospedale Maggiore Policlinico, Milan, and by a COVID-19 research grant from the European Society of Endocrinology. Dr. Muller and Dr. Lash have reported no relevant financial relationships.
A version of this article first appeared on Medscape.com.