Overview of Acute Infectious Thyroiditis

Acute infectious thyroiditis is a rare thyroid gland infection. This type of infection is painful, associated with a fever, and progresses rapidly. It can affect children and adults. Acute infectious thyroiditis can often be treated with antibiotics and a procedure that drains the fluid and pus.

Symptoms

Acute infections, by definition, are the type of infections that cause symptoms within a short period of time. If you or your child develop acute infectious thyroiditis, you can expect the effects to rapidly worsen.

Symptoms may include:

• Rapid onset of pain and tenderness in one side of your neck
• Fever and chills (a flu-like feeling)
• Enlarged thyroid gland or swelling in your neck area
• A movable lump in your neck
• A warm, red, or tender area in the neck
• Painful swallowing
• Swollen lymph glands

You can also develop symptoms of hypothyroidism (low thyroid hormone function) or hyperthyroidism (excess thyroid hormone function), although your thyroid function is likely to remain stable during a bout of acute infectious thyroiditis. 

Complications

Acute infectious thyroiditis can produce a number of complications, the most common of which is an abscess, an encapsulated (closed-off) infection that is difficult to treat with antibiotics.

Other potential complications can include:

• Systemic infection, which is the spread of the infection to another part of your body, is a rare complication.
• Bleeding into the thyroid gland can occur, resulting in swelling, possible respiratory symptoms, and damage to the thyroid gland.
• While it is uncommon, long-term thyroid dysfunction due to damage to the thyroid gland can occur after the infection is completely resolved

Causes

Infectious thyroiditis is usually caused by a bacterial infection. Most often, the culprit is a Gram-positive bacterium such as S. aureus or Streptococci. Gram-negative organisms involving the oropharynx can also be to blame. Less commonly, acute infectious thyroiditis can be caused by mycobacteria or fungi—this is rare, and typically only affects immunocompromised individuals.

Risk factors include:

• Time of year, as this infection is more common in the fall and winter, especially after an infection of the upper respiratory tract.
• Age affects the risk, with only about 8% of acute infectious thyroiditis estimated to occur in adults. Subacute thyroiditis is most common in young adulthood and middle age, and it decreases in frequency with increasing age.
• A piriform sinus fistula, which is a congenital (from birth) defect in the areas around the nose, mouth, and neck, leads to an increased risk of developing this infection. The fistula can permit bacterial organisms to have access to the thyroid gland.
• A weakened immune system can be caused by immunosuppressive medication, chemotherapy drugs, or a medical condition such as HIV.
• Thyroid cancer increases the risk of developing an acute thyroid infection.
• Intravenous (IV) drug use makes you more susceptible to developing a severe bacterial infection and has been associated with acute infectious thyroiditis.

While thyroid gland infection is rare, subacute or chronic thyroid infections are more common and less severe than acute infectious thyroiditis. Acute infectious thyroiditis is usually caused by bacteria, whereas subacute thyroid infections are usually caused by a virus, and are therefore treated with different medications.

Diagnosis

If your healthcare provider suspects that you have acute infectious thyroiditis, you will need a medical evaluation to confirm the diagnosis and to identify any risk factors. Your healthcare provider will examine your neck and look for signs of infection elsewhere in the body.

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Physical Examination

The most common signs of acute infectious thyroiditis are a fever and neck tenderness.

Along with a thorough general physical examination, your healthcare provider will gently palpate (feel) your neck and thyroid gland, as well as nearby lymph nodes to check the size and texture of any growth.

Diagnostic Imaging Tests

Your healthcare provider may order one or more imaging tests to visualize the structures in your neck. Diagnostic examinations may include a neck ultrasound, computerized tomography (CT) scan, magnetic resonance imaging (MRI), or a thyroid uptake scan.

These imaging tests can help identify whether your symptoms are caused by thyroiditis or by another infection or disease involving the neck. Anatomical variations, like a fistula, can be identified as well. However, imaging might not distinguish infectious thyroiditis from subacute (noninfectious) thyroiditis.

Blood Tests

You may need blood tests. A complete cell count (CBC) can show an elevated white blood cell count with an infection. Thyroid function tests are usually altered by non-infectious inflammation of the thyroid gland, like non-infectious thyroiditis.

A blood culture may also be helpful in identifying bacteria or another microorganism that's causing your infection. Your healthcare provider may also run other blood tests to identify whether you have an undiagnosed problem with your immune system.

Fine Needle Aspiration

Sometimes, an aspiration test can help identify whether thyroiditis is suppurative (contains pus) or non-suppurative. Suppurative infectious thyroiditis is usually more severe than non-suppurative thyroiditis.

Fine needle aspiration (FNA) is a procedure that involves withdrawing some of the fluid or tissue from your thyroid gland. In some cases, the FNA is guided by ultrasound to determine the position and location of an infection or abscess.

The sample will be analyzed using a culture, which is a material that allows infectious organisms to grow so that they can be identified. The culture results can help your healthcare provider choose the appropriate antibiotic and/or anti-fungal medication for treatment.

Treatment

The treatment of acute thyroiditis is focused on eliminating the infection and reducing symptoms while the infection resolves. There are several treatments that can be used, and, if you or your child has acute infectious thyroiditis, your healthcare providers will initiate treatment quickly.

The usual treatment for acute infectious thyroiditis is a combination of incision and drainage coupled with antibiotics.

In addition to treatment for your infection, you may also need medication to lower your fever and/or treatment for pain. If you are unable to eat, you may need IV fluids until you are able to resume eating.

Antibiotics

Oral antibiotics can be used for the treatment of acute bacterial infectious thyroiditis. Some of the antibiotic medications that are commonly used for this type of infection include penicillin, clindamycin, or a combination of macrolide and metronidazole.

If your healthcare provider is concerned that you could have an antibiotic-resistant infection, another antibiotic may be selected. Antibiotic-resistant infections are bacteria that do not respond to standard antibiotics, often called "superbugs," and they require treatment with antibiotics that are stronger and/or more specifically directed.

You may need treatment with an intravenous (IV) antibiotic if your healthcare provider is concerned that your infection is progressing rapidly, if you can't swallow oral medication, or if you are vomiting so much that you can't absorb oral medication.

Procedures

Percutaneous drainage is a procedure that your healthcare provider may use to remove the infectious fluid with a needle. You may have percutaneous drainage at the same time as your FNA. If you have this procedure, you will probably also receive antibiotic treatment.

Infrequently, surgical drainage of an infection or an abscess is required if your infection does not improve with percutaneous drainage and antibiotic therapy.

Rarely, surgical removal of part of the thyroid gland may be needed. In some cases, removal of half the thyroid gland, known as a hemithyroidectomy, may provide more effective treatment.

A Word From Verywell

Infection of the thyroid gland is rare. If you are diagnosed with this type of infection, you can anticipate rapid treatment and a quick recovery. Thyroid infections generally respond well to treatment, although there is a risk of recurrence if there is an associated fistula or if you have other risk factors.