Subacute Thyroiditis: Introduction, Pathogenesis, symptoms and treatment

What Is Subacute Thyroiditis?

Thyroiditis refers to an inflamed thyroid. Your thyroid is a gland in the front of your neck that controls your metabolism by releasing a variety of hormones.

Most types of thyroiditis do not cause pain in the thyroid gland. However, they typically lead to either hyperthyroidism (overactive thyroid) or hypothyroidism (underactive thyroid). Both of these conditions cause

symptoms such as weight changes, anxiety, and fatigue.

Subacute thyroiditis leads to pain and discomfort in the thyroid gland. Individuals with this condition will also have symptoms of overactive thyroid and later develop symptoms of underactive thyroid.

Subacute thyroiditis generally occurs after an upper respiratory viral infection such as the flu or the mumps. The mumps is a highly contagious viral infection that causes inflamed salivary glands. Subacute thyroiditis is very rare. However, it is slightly more common in middle-aged women.

Pathogenesis:

Subacute thyroiditis is presumed to be caused by a viral infection or a post-viral inflammatory process. The majority of patients have a history of an upper respiratory infection prior to the onset of thyroiditis (typically two to eight weeks beforehand). The disease was thought to have a seasonal incidence (higher in summer), and clusters of cases have been reported in association with Coxsackie virus, mumps, measles, adenovirus, and other viral infections. However, in other series, there was a relatively comparable distribution of presentation throughout the year. Serial studies of viral antibody titers have implicated many of the same viruses, but the changes could equally be attributed to nonspecific anamnestic responses. Viral inclusion bodies are not seen in thyroid tissue.

Thyroid autoimmunity does not appear to play a primary role in the disorder, but it is strongly associated with HLA-B35 in many ethnic groups. A unifying hypothesis might be that the disorder results from a common subclinical viral infection that provides an antigen, either of viral origin or resulting from virus-induced host tissue damage, that uniquely binds to HLA-B35 molecules on macrophages. The resulting antigen-HLA-B35 complex activates cytotoxic T lymphocytes that then damage thyroid follicular cells, because the cells have partial structural similarity with the infection-related antigen. Unlike autoimmune thyroid disease, however, the immune reaction is not self-perpetuating, so the process is limited.

Whatever factors initiate subacute thyroiditis, the resulting thyroid inflammation damages thyroid follicles and activates proteolysis of the thyroglobulin stored within the follicles. The result is unregulated release of large amounts of thyroxine (T4) and triiodothyronine (T3) into the circulation resulting in clinical and biochemical hyperthyroidism. This state lasts only until the stores of thyroglobulin are exhausted because new hormone synthesis ceases, not only because of damage to the thyroid follicular cells but also because of inhibition of thyrotropin (TSH) secretion by the increased serum T4 and T3 concentrations.

As the inflammation subsides, the thyroid follicles regenerate and thyroid hormone synthesis and secretion resume. There is usually a period of rapid evolution through euthyroidism and then into hypothyroidism. The hypothyroidism lasts until the thyroid gland can generate sufficient thyroid hormone synthesis and secretion so that the patient regains normal homeostasis. Each phase typically lasts two to eight weeks with the possible exception of the initial transition through euthyroidism, which may be shorter

Symptoms of Subacute Thyroiditis:

Unlike other forms of thyroid inflammation, this condition causes pain in your thyroid gland. In some cases, this pain might also occur in other parts of your neck, your ears, or your jaw. Your thyroid may be tender and swollen to the touch.

Other symptoms of this condition include:

• fatigue
• metabolism issues (such as weight changes and difficulty regulating body temperature
• weakness

You will typically develop hyperthyroidism in the initial stages of this condition. Your symptoms during this stage of the disease may include:

• mental or emotional difficulties (such as nervousness, irritability, restlessness, trouble concentrating)
• fatigue
• increased body temperature (leading to excessive sweating)
• weight loss
• fast or irregular heartbeat

As the disease progresses, hypothyroidism generally replaces hyperthyroidism. You will typically develop a new set of symptoms, including:

• fatigue, lethargy, weakness, and sluggishness
• constipation
• weight gain
• heavy menstrual periods

According to the American Thyroid Association, the first stage of the condition usually lasts for less than three months. The second stage may last for an additional nine to 15 months (ATA, 2012).

How Is Subacute Thyroiditis Diagnosed?

Your doctor will diagnose this condition using blood tests. The results of these tests will vary depending on the disease’s stage. For example, in the initial stages, your thyroid hormone (free T4) levels will be elevated, while your TSH (thyroid stimulating hormone) levels will be low.

The free T4 and TSH levels are part of an internal feedback loop. When one is high, the other is low and vice versa. In the later stages of the disease, your TSH levels will be elevated while your T4 levels will be low.

Your doctor will also diagnose this condition based on your recent medical history. Your doctor will be more likely to check for this condition if you have recently had an infection. This is because subacute thyroiditis usually develops after a viral infection.

Pain in your thyroid gland is another clue that you have this condition.

How Is Subacute Thyroiditis Treated?

Your doctor will give you medications to help reduce the pain and control inflammation. This is the only treatment necessary in some cases. Possible medications include steroids, aspirin, and ibuprofen.

Your doctor may also want to treat this condition using beta-blocker medications if hyperthyroidism is present in the early stages. These medications lower blood pressure and reduce symptoms such as irregular heartbeat and nervousness.

However, the treatments for overactive thyroid will be temporary. Your doctor will eventually wean you off any medications that had been prescribed to treat the condition.

Keep in mind that the disease usually occurs in two stages. Treatment for overactive thyroid is important at the beginning of the disease. However, it will not be helpful once your condition progresses into the second phase.

During the later stages of the disease, you will have underactive thyroid. You will generally need to take hormones to replace those that your body is not producing.

What Is the Outlook for Subacute Thyroiditis?

Symptoms will resolve within a year and a half on their own in the majority of cases. However, hypothyroidism may end up being permanent. The ATA estimates that this occurs in approximately five percent of cases (ATA, 2012).

Ref:    www.healthline.com

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