Subacute Thyroiditis: Inflammation and Its Impact on the Thyroid

Subacute thyroiditis may be more than just a "pain in the neck" – both literally and figuratively. This inflammatory and painful thyroid condition causes shifts in thyroid hormones, resulting in temporary hyperthyroidism or hypothyroidism. Though relatively rare, affecting around 5 in 100,000 people each year, subacute thyroiditis can cause significant discomfort and permanent complications if left unaddressed.

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What Is Subacute Thyroiditis?

Thyroiditis refers to inflammation of the thyroid gland that leads to changes in thyroid function, often resulting in either hypothyroidism (underactive thyroid) or hyperthyroidism (overactive thyroid). This inflammation can be classified as painful or painless, with various causes ranging from autoimmune conditions to infections to medication side effects. 

Subacute thyroiditis, also called granulomatous or de Quervain thyroiditis, is the most common type of painful thyroiditis. It is a self-limited condition that typically follows a distinct course, starting with an initial phase of hyperthyroidism, progressing to a period of hypothyroidism, and then returning to normal thyroid function (euthyroidism). (19, 26)

Causes and Risk Factors

Subacute thyroiditis is thought to be triggered by a viral infection that causes a post-viral inflammatory response within the thyroid gland.

Common infections linked to the condition include upper respiratory infections caused by the following viruses (26): 

• Mumps
• Measles
• Coxsackievirus
• Influenza
• Adenovirus
• Echovirus
• Severe acute respiratory syndrome coronavirus 2 (SARS-CoV2) 

Risk factors for developing de Quervain thyroiditis include (26): 

• Gender: Women are affected 4-5 times more often than men
• Age: Peak incidence occurs between the ages of 25-35, and then decreases in frequency with increasing age
• Season: Most cases occur in the summer and the fall
• Genetics: People with the human leukocyte antigen (HLA)-Bw35 gene are six times more likely to develop subacute thyroiditis than the general population. 

Symptoms of Subacute Thyroiditis

The clinical course of subacute thyroiditis is predictable, following three distinct phases (15): 

1. Thyrotoxic Phase: the thyroid is inflamed and releases too many hormones, causing temporary thyrotoxicosis (hyperthyroidism). This phase lasts 4-10 weeks. 
2. Hypothyroid Phase: The thyroid cannot produce sufficient amounts of hormones, causing hypothyroidism. This phase may last up to two months. 
3. Euthyroid Phase: As thyroid cells regenerate, normal thyroid function is restored in 90-95% of patients.

The classic symptom of subacute thyroiditis is pain in the neck that can radiate to the jaw or ears. This pain may last for weeks to months. Other symptoms related to thyroid inflammation include:

• Difficulty swallowing
• Painful swallowing
• Hoarseness of the voice
• Fatigue
• Fever (22) 

Patients will feel different symptoms in each phase related to the amount of thyroid hormone in circulation. 

Hyperthyroid symptoms include (9):  

• Anxiety, irritability, and nervousness
• Rapid heart rate
• Heart palpitations
• Unintentional weight loss
• Increased appetite
• Hair loss
• Light or infrequent menstrual periods
• Tremor and shaking
• Increased sweating and body temperature
• Diarrhea
• Muscle weakness
• Insomnia

Hypothyroid symptoms include (9): 

• Depression
• Unintentional weight gain
• Dry skin
• Brain fog
• Cold body temperature
• Joint and muscle pain
• Heavy menstrual periods
• Constipation

Diagnosing Subacute Thyroiditis

The diagnosis of subacute thyroiditis is primarily clinical, based on the presence of an enlarged, tender thyroid in patients with a clinical history of post-viral thyroiditis symptoms. Approximately 50% of patients will present to their doctor during the first weeks of illness with symptoms of hyperthyroidism.

Laboratory tests and imaging that can be performed include (22):  

• Thyroid-stimulating hormone (TSH)
• Free thyroxine (fT4)
• Free triiodothyronine (fT3)
• Thyroid antibodies
• Erythrocyte sedimentation rate (ESR)
• C-reactive protein (CRP)
• Thyroid ultrasound
• Radioactive iodine uptake test

Common laboratory findings include (14): 

• Thyrotoxic phase: TSH levels are low, and fT4 and fT3 are high
• Hypothyroid phase: TSH levels are high, and fT4 and fT3 are low
• Thyroid antibodies low or absent
• ESR elevated (> 50 mm/hr) 
• CRP elevated

Ultrasound features suggestive of subacute thyroiditis include (14): 

• Heterogeneous hypoechogenicity: the thyroid tissue appears uneven (heterogeneous) and looks darker than normal (hypoechoic)
• Reduced vascularity: there is less blood flow to the thyroid than usual

A radioactive iodine uptake (RAIU) test is the preferred imaging test to determine the cause of abnormal thyroid function tests. RAIU is low or near zero during the thyrotoxic phase of subacute thyroiditis (15).  

Treatment Options for Subacute Thyroiditis

Subacute thyroiditis is self-limited, with the thyroid gland spontaneously returning to normal function after several months. Therefore, the primary goals of treatment are relieving thyroid pain and managing the symptoms related to thyroid dysfunction. (34)  

Managing Pain and Inflammation

High-dose aspirin (2,600 mg per day in divided doses) or ibuprofen (3,200 mg per day in divided doses) are both appropriate first-line options for pain management (23). 

If severe neck pain has not improved with either of these options after four days, consider an oral corticosteroid, such as 30-40 mg of prednisone daily for 5-7 days, followed by a steroid taper for the next 30 days.

Complementary and integrative medicine modalities that have evidence to support their use in pain management include: 

• Hydrotherapy
• Acupuncture

Addressing Thyroid Dysfunction

The American Thyroid Association (ATA) recommends using beta-blockers to treat symptoms in the initial hyperthyroid phase of subacute thyroiditis, especially in the following groups: 

• Elderly patients
• Patients with preexisting cardiovascular disease
• Patients with resting heart rates exceeding 90 beats per minute

Beta-blockers can alleviate the following symptoms of hyperthyroidism:

• Heart palpitations
• Tachycardia
• Tremors
• Anxiety
• Heat intolerance

The hypothyroid phase of subacute thyroiditis is usually mild and typically does not require treatment (15). ATA treatment guidelines recommend levothyroxine (synthetic T4 replacement) for symptomatic patients with elevated TSH until thyroid function returns to normal (21).  

Patients can also consider supplementing with vitamin and mineral cofactors required for proper thyroid function. 

• Selenium supports the production of thyroid hormones and protects the thyroid gland from oxidative stress.
• Vitamin D deficiency is a risk factor for many thyroid disorders. Serum vitamin D is often measured considerably lower in patients with subacute thyroiditis than in healthy controls.
• Zinc deficiency can impair thyroid hormone production, receptor sensitivity, and antioxidant systems that protect the thyroid from oxidative stress.

The Course and Prognosis of Subacute Thyroiditis

Subacute thyroiditis is generally self-limited, with patients returning to a euthyroid state within a few months. Recurrence is uncommon but can occur in up to 2% of patients. In rare cases (5-10%), irregular scarring of the thyroid gland can result in permanent hypothyroidism, requiring life-long thyroid hormone replacement therapy. (14, 26)

Preventing Recurrences and Managing Long-Term Impact

To prevent subacute thyroiditis, focus on strategies that can minimize the risk of viral infections and reduce inflammation (35, 36):   

• Good Hygiene Practices: Wash your hands regularly and cover your mouth when coughing or sneezing to prevent the spread of germs.
• Vaccinations: Stay up-to-date on relevant vaccinations. 
• Avoid Close Contact With Sick Individuals: Limit exposure to sick people, especially during cold and flu season.
• Healthy Diet: Eat an anti-inflammatory diet rich in vitamins, minerals, and antioxidants to support the immune system.
• Healthy Lifestyle: Maintain a healthy lifestyle through regular exercise, adequate sleep, and stress management.

When to Seek Medical Help

It is important to seek medical help when at the first sign of thyroid dysfunction: 

• Severe neck pain
• Difficulty swallowing
• Symptoms of hypothyroidism or hyperthyroidism

After recovering from subacute thyroiditis, consult a healthcare provider if you experience residual or recurrent symptoms of thyroid imbalance. Ongoing thyroid dysfunction can lead to significant health issues, and a healthcare professional can provide appropriate testing and management to ensure your thyroid health is adequately monitored and maintained.

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Key Takeaways

• Subacute thyroiditis is a temporary but impactful condition characterized by thyroid inflammation that can lead to fluctuations in thyroid hormone levels and associated symptoms such as neck pain and fatigue. 
• With appropriate treatment and regular follow-up, most people can achieve full recovery of thyroid function without long-term consequences.
• Adopting daily habits to support the immune system and reduce inflammation may prevent subacute thyroiditis from becoming a literal pain in your neck.