Subacute thyroiditis in Covid-19 patients

Many of you will be aware of the media reports about some Covid-19 patients developing subacute (viral) thyroiditis. This can develop either during the acute phase of Covid-19 infection or a few weeks post infection. It is different from ‘non thyroidal illness’, which can occur in people who are very sick. In this second scenario, T4, T3 and TSH all go down as the body attempts to conserve energy and divert it towards survival. Once the acute illness is over, thyroid levels generally restore themselves.

We have understandably received enquiries about ‘Post Covid-19 subacute thyroiditis’ including: How can I manage my symptoms? Is it temporary or will it develop into permanent hypothyroidism? Could it be one of the ‘Long Covid-19' symptoms we are hearing about?

What is subacute thyroiditis?

This is usually a temporary condition believed to be caused by a viral infection, usually associated with pain or tenderness in the thyroid gland, and sometimes also sore throat, flu-like symptoms and/or fever. There is a period of increased thyroid hormones circulating in the blood . During this phase you may experience symptoms such as nervousness, tremor, palpitations, insomnia and feeling warmer than usual. This is sometimes followed by a period of reduced thyroid function (hypothyroidism), when you may experience the opposite symptoms I.e. slowness, fatigue and feeling colder than usual. In some patients, subacute thyroiditis resolves itself without treatment, or with the help of anti-inflammatory drugs (i.e. steroids). You will usually recover completely in two to five months although in five to twenty per cent of cases it may lead to permanent thyroid hypofunction.  In these cases, you will be prescribed levothyroxine.

Researchers have been studying the rate of subacute thyroiditis in Covid-19 patients.

We recently talked to Dr Ilaria Muller about her, and her colleagues’, study. This looked at the prevalence of thyrotoxicosis* (suggestive of subacute thyroiditis) in Covid-19 patients. These patients were admitted to the High Intensity of Care Unit (HICU) in Milan’s main public hospital.

What was the aim of the research?

Our initial analysis of Covid-19 patients admitted to the HICU in Milan's hospital showed these individuals commonly had low or suppressed Thyroid Stimulating Hormone (TSH). In some patients their free thyroxine concentrations were raised, in others they were not. This suggests thyrotoxicosis, due to increased production (overactive thyroid or hyperthyroidism) or release of thyroid hormones.

Whilst critically ill patients can often have alterations in their TSH and thyroid hormone levels (known as non-thyroidal illness syndrome), it is possible the thyrotoxicosis is a result of SARS-CoV-2 (Covid 19) directly infecting the thyroid gland and causing subacute thyroiditis in patients. 

In our study we wanted to establish to what extent thyrotoxicosis, suggestive of subacute thyroiditis (rather than non-thyroidal illness) was present in patients, with or without Covid-19, being treated in intensive care units.

What did your study involve?

We compared a group of HICU patients admitted in 2020 for Covid-19 disease with a similar group admitted to HICU before the Covid-19 pandemic in 2019. We also compared the 2020 group to a smaller group of Covid-19 patients admitted to Low Intensity of Care Unit (LICU) in 2020. The study took place in the Fondazione IRCCS Ca' Granda Ospedale Maggiore Policlinico, Milan, Italy.

What about patients who already had thyroid disease at the time of their hospital admission?

Thyroid disorders are very common, so we expected several Covid-19 patients would be admitted to HICU with pre-existing thyroid conditions or already taking thyroid medication. We excluded these patients from our study as we wanted to pick up thyroid abnormalities very likely related to Covid-19 only, and not to other factors (I.e. inadequate dose of thyroid medication or uncontrolled thyroid disease), which would have biased our study.

What were your findings and why are they significant?

We observed thyrotoxicosis suggesting subacute thyroiditis was more frequent in patients with severe Covid-19 disease. From our study of 85 HICU 2020 Covid-19 patients 13 (15%) had thyrotoxicosis. Of the 41 Covid-19 patients admitted to the LICU unit, only 1 (2%) had thyrotoxicosis. And just 1 (1%) of the 78 HICU patients admitted in 2019 (before Covid-19) had thyrotoxicosis. Furthermore average TSH values were lower in the HICU 2020 Covid-19 than the other two patient groups. Of the overall 14 patients with Covid-19 showing thyrotoxicosis, 64% (9) were men and 36% (5) women We believe Covid-19 may have induced an atypical form of subacute thyroiditis in these patients.  It is atypical since it does not present with neck pain, and does not seem to affect predominantly women, as the case of the classic form. 

Were there any limitations to the study?

 Ideally TSH, FT4 and FT3 would have been tested in all patients to help establish whether reduced TSH values in the HICU patients were due to non-thyroidal illness syndrome, subacute thyroiditis or a combination of the two. We were also only able to perform thyroid imaging studies nearly two months afterwards. This was because patients needed to quarantine until they had had two negative Covid-19 tests. This meant we could study only a minority of patients, and we might have missed imaging signs of thyroiditis in some of them.

What are the next steps?

We are calling for routine assessment of thyroid function in Covid-19 patients requiring intensive care treatment. This is because they frequently present with thyrotoxicosis due to an atypical form of subacute thyroiditis induced by Covid-19. Other early independent studies produced in the meantime also seem to confirm our results. We are also asking for long-term monitoring of these patients to assess their thyroid (dys) function through time.  It is also important to perform cytology/histology studies to investigate the mechanisms of the thyroid damage, since it likely differs from that of classic subacute thyroiditis induced by other viruses.

Do you believe thyroid dysfunction may be one of the 'long Covid 19' symptoms being discussed in the media?

Yes, it might. Although the thyroid abnormalities seem to be transient, permanent thyroid dysfunction might come back in the long term. This is commonly seen in classic subacute viral thyroiditis.

I would like to thank all my colleagues, especially Dr Mario Salvi and Dr Daniele Cannavaro, and the patients involved in this study

Read the full study at

BTF leaflet on thyroiditis


*Thyrotoxicosis describes the clinical effects experienced due to an excess of thyroid hormones in the bloodstream. It is sometimes interchanged with the term ‘hyperthyroidism’, although their meanings are slightly different.

The main cause of thyrotoxicosis is hyperthyroidism when overactivity in the thyroid gland produces excess levels of thyroid hormone, as in Graves’ disease (autoimmune hyperthyroidism), toxic multinodular goitre or thyroid adenoma. Less frequent causes of thyrotoxicosis (but not hyperthyroidism) are an excessive intake of thyroid hormone in people being treated for hypothyroidism, an increased release of pre-formed and stored thyroid hormones from the thyroid gland due to its inflammation and damage (thyroiditis) . This can have many causes, such as infections, autoimmunity, and even as a side effect of certain medications (i.e. amiodarone).

Covid-19 resources

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