Thyroiditis

Etiology and Pathophysiology

Thyroiditis, or inflammation of the thyroid gland, has multiple etiologies, including autoimmune conditions, infectious agents, and iatrogenic causes. Each causative condition has a specific pathologic mechanism.

Clinical Presentation

• Goiter → mass effect leading to:
  • Discomfort and/or globus sensation
  • Dysphagia
  • Dyspnea and/or stridor
  • Hoarseness
• Specific signs and symptoms depend on the underlying cause:
  • Hashimoto’s thyroiditis: 
    • Initially asymptomatic
    • Painless, symmetrical goiter develops.
    • Transient hyperthyroidism followed by permanent hypothyroidism
  • Riedel’s thyroiditis: presents along with symptoms of tracheal compression
  • Subacute (De Quervain) thyroiditis: fever with a painful, enlarged and tender thyroid on palpation (goiter)
  • Suppurative thyroiditis: 
    • Sudden onset of neck pain, usually unilateral
    • Fever, dysphagia, and leukocytosis
• Triphasic clinical course: presents in painless, postpartum, and subacute thyroiditis 
  • Thyrotoxicosis occurs owing to increased release of preformed/stored thyroid hormones and suppression of TSH and lasts 4–6 weeks.
  • As stores are depleted, and TSH is already suppressed, a hypothyroidism phase begins. This phase lasts 4–6 months.
  • TSH will subsequently rise and increase thyroid hormone production, leading to normalization of thyroid function. This phase lasts for several months after onset.

Diagnosis

• The signs and symptoms of thyroiditis will be characteristic of their respective thyroid hormone levels (hypothyroidism versus hyperthyroidism).
• Goiter characteristics should be examined via palpation.
• Thyroid function test results will depend on the clinical phase:
  • Thyrotoxicosis: ↑ T₃ and T₄, ↓ TSH
  • Hypothyroid phase: ↓T₃ and T₄, ↑ TSH
  • Euthyroid phase: normal levels of T₃, T₄, and TSH
• Ultrasonography:
  • Infectious thyroiditis presents with abscesses.
  • Subacute thyroiditis presents with diffuse heterogeneity and low vascular flow.
• Fine-needle aspiration:
  • Infectious thyroiditis shows fluid collection with microbes.
  • Subacute thyroiditis shows multinucleated giant cell granulomas.
• Thyroid peroxidase and thyroglobulin antibodies will be present in Hashimoto’s thyroiditis.
• Radioactive iodine uptake will usually be low.

Management

The type of therapy used will depend on which phase the patient presents or the specific cause of the condition.

• Thyrotoxicosis phase: antithyroid medication should not be used
  • Nonspecific beta-blockers block peripheral conversion of T₄ to T₃.
  • NSAIDs in the case of painful goiters (e.g., infectious thyroiditis)
• Hypothyroid phase: lifelong oral administration of L-thyroxine
• Riedel’s thyroiditis may require prednisolone and surgical relief of compressive symptoms.

Differential Diagnosis

The differential diagnosis of thyroiditis depends on the differentiation/recognition of the various conditions that can produce inflammation of the thyroid gland. The following are the most common causes and their characteristic presentations.

• Subacute thyroiditis (De Quervain’s thyroiditis): Patients present with hyperthyroidism, followed by hypothyroidism and then recovery. During the hyperthyroid phase, the patient presents with neck pain, a tender diffuse goiter, and elevated levels of T₃ and/or T₄.
• Acute infectious thyroiditis with abscess formation is caused by gram-positive or gram-negative organisms, usually in immunocompromised patients. The organisms most commonly involved are staphylococci and streptococci. The patient presents with sudden onset of neck pain and tenderness that is usually unilateral and accompanied by fever and chills. Ordinarily, patients have a unilateral neck mass, which can fluctuate. Thyroid function is often normal, but thyrotoxicosis may be present.
• Chronic infectious thyroiditis: usually presents as bilateral disease: The pain and tenderness are less prominent than in acute infections. Patients might present with hypothyroidism.
• Radiation thyroiditis: Some patients with hyperthyroidism treated with radioiodine develop thyroid pain and tenderness 5 to 10 days later due to a radiation-induced injury and necrosis of the thyroid follicular cells and associated inflammation. Patients present with neck pain and tenderness, which is usually mild and disappears in a few days. Transient exacerbation of hyperthyroidism is possible.
• Riedel’s thyroiditis: presents as neck discomfort or tightness with dysphagia or hoarseness and a diffuse, asymmetric goiter that is very hard, fixed, and often not clearly defined: Most patients with Riedel’s thyroiditis are euthyroid, and only a few are hypothyroid. Serum antithyroid antibody concentrations are often high in these patients.