The Thyroid Gland After Infections: Thyroiditis and Autoimmune Disorders

Introduction: The Link Between Infections and the Thyroid Gland

The relationship between infectious diseases and the development of thyroid pathologies has long been a focus of medical attention. However, the COVID-19 pandemic has significantly expanded our understanding of how viral infections can affect the endocrine system, particularly the thyroid gland. An increasing number of clinical cases and studies indicate that SARS-CoV-2 is capable of triggering or exacerbating various forms of thyroiditis and autoimmune thyroid diseases [1, 2, 3, 5].

How Does COVID-19 Affect the Thyroid Gland?

The SARS-CoV-2 virus is known for its ability to trigger multiple immune responses, which can lead to the development of various autoimmune diseases, including thyroid pathologies [3]. The mechanisms of this influence are not fully understood, but it is hypothesized that the virus may directly damage thyroid cells or, more likely, cause dysregulation of the immune system, which then begins to attack the body's own tissues [1, 2].

Such immune "reprogramming" can manifest in different ways:

• New-onset disease: Patients who previously had no thyroid issues may develop autoimmune thyroiditis after recovering from COVID-19 [1, 2].
• Exacerbation of existing conditions: In people with already diagnosed but stable autoimmune thyroid diseases (e.g., Hashimoto's thyroiditis), the infection can trigger a flare-up or even a transition to another form of the disease, such as Graves' disease [3].

Studies show a temporal link between a COVID-19 infection and the subsequent development of thyroid dysfunction, highlighting the potential impact of the virus on the immune system and the gland itself [1, 2]. Infodemiological studies analyzing Google search queries have also revealed an increase in interest in terms related to the thyroid gland and thyroiditis, parallel to the rise in COVID-19 cases, which may reflect the real epidemiological picture [4].

Variety of Thyroiditis After COVID-19

Various forms of thyroid disease can develop after a coronavirus infection. A systematic review including 46 studies and more than 3,800 patients confirms that COVID-19 can induce or exacerbate autoimmune thyroid disorders [5]. The most common conditions encountered are:

• Hashimoto's Thyroiditis (autoimmune hypothyroidism): This is a condition in which the immune system attacks the thyroid gland, leading to chronic inflammation and reduced function. In one described case, a 38-year-old woman developed hypothyroidism 6 weeks after COVID-19, having had no prior thyroid problems [1].
• Graves' Disease (autoimmune hyperthyroidism): In this disease, the immune system produces antibodies that stimulate the thyroid gland to overproduce hormones. Cases of Graves' disease were recorded in a 33-year-old woman 8 weeks after COVID-19 [1] and in a 28-year-old woman, also with no prior history of thyroid disease [2]. Moreover, in patients with stable Hashimoto's thyroiditis, cases of transition to Graves' disease were observed after COVID-19 [3].
• Subacute Thyroiditis: This is an inflammatory thyroid disease that often occurs after viral infections. COVID-19 has also been linked to its development [1].

These cases underscore that COVID-19 can be a trigger for a wide spectrum of autoimmune and inflammatory thyroid diseases, both in previously healthy individuals and in those who already had a predisposition.

Symptoms to Pay Attention To

Symptoms of thyroid diseases can be diverse and are often non-specific, which complicates timely diagnosis, especially after an infection. It is important to be attentive to changes in your well-being.

Symptoms of hypothyroidism (reduced thyroid function), characteristic of Hashimoto's thyroiditis:

• Increased fatigue, weakness
• Weight gain despite normal diet
• Dry skin, brittle hair and nails
• Feeling cold, intolerance to low temperatures
• Constipation
• Swelling of the face and limbs
• Slowed thinking, reduced concentration

Symptoms of hyperthyroidism (increased thyroid function), characteristic of Graves' disease:

• Rapid heartbeat, arrhythmias
• Weight loss with a normal or increased appetite
• Nervousness, irritability, anxiety
• Hand tremors
• Increased sweating, heat intolerance
• Sleep disturbances
• Bulging eyes (exophthalmos) and other eye symptoms (thyroid eye disease), which can significantly impair quality of life [7]

Symptoms can vary in severity from mild to severe, significantly affecting daily life and mental health [7]. If you notice such changes after an infection, especially COVID-19, do not delay a visit to the doctor.

When to See a Doctor and What to Expect?

If you notice one or more of the above symptoms after an infection such as COVID-19, it is crucial to consult an endocrinologist. Timely diagnosis and the start of treatment significantly improve the prognosis and quality of life.

Diagnosis usually includes:

• Blood test for thyroid hormones: Determination of thyroid-stimulating hormone (TSH), free thyroxine (free T4), and free triiodothyronine (free T3) levels [1, 2].
• Blood test for antibodies: Determination of anti-thyroid peroxidase antibodies (anti-TPO) and anti-TSH receptor antibodies (TRAb) to identify the autoimmune nature of the disease [1, 2].
• Thyroid ultrasound: To assess size, structure, and the presence of nodules.

Treatment:

• For hypothyroidism (e.g., Hashimoto's thyroiditis), hormone replacement therapy with synthetic thyroxine (levothyroxine) is prescribed [1].
• For hyperthyroidism (e.g., Graves' disease), antithyroid drugs (e.g., methimazole or thiamazole) are used to suppress hormone production, as well as beta-blockers to manage symptoms such as rapid heartbeat [2].

In most cases, with timely initiation of therapy, patients respond well to treatment, and their condition stabilizes [2]. Therefore, do not ignore alarming symptoms and be sure to consult a specialist.

Sources

1. Manifestations of thyroid disease post COVID-19 illness: Report of Hashimoto thyroiditis, Graves' disease, and subacute thyroiditis.
2. Thyroid disease post-COVID-19 infection: Report of a case with new-onset autoimmune thyroid disease.
3. Development of autoimmune thyroid disease after COVID-19 infection: case report.
4. COVID-19 and thyroid disease: An infodemiological pilot study.
5. Autoimmune Thyroid Diseases After COVID-19 Infection: A Systematic Review of Clinical Manifestation and Outcomes.
6. Thyroid disease in ANCA-associated vasculitis: a clinical and epidemiological study.
7. Impacts of Thyroid Eye Disease (TED), Beyond the Signs and Symptoms: Results from the ElevaTED Patient Survey.
8. To Lighten the Burden of Cure: Thyroid Disease in Long-Term Survivors After TBI Conditioning for Paediatric ALL.

The information provided in this article is for reference purposes only and cannot replace professional medical advice. Always consult a qualified specialist for the diagnosis and treatment of diseases.