49. Thyroiditis - classification, etiology, pathogenesis, clinical manifestations.

Thyroiditis - classification, etiology, pathogenesis, and clinical manifestations.

Thyroiditis refers to inflammation of the thyroid gland, which can lead to transient hyperthyroidism, hypothyroidism, or both, depending on the type and stage.

Classification

1. 1 According to clinical course

1. 2 According to etiology

Etiology

Acute thyroiditis

• Bacterial infections (e.g., Staphylococcus, Streptococcus).
• Less commonly fungal infections.

Subacute thyroiditis (De Quervain )

• Usually preceded by viral infection (e.g., mumps, coxsackievirus, adenovirus).
• Chronic autoimmune thyroiditis (Hashimoto)
• Autoimmune; anti-thyroid peroxidase (anti-TPO) and anti-thyroglobulin antibodies.
• Genetic predisposition (HLA-DR5).
• Fibrous thyroiditis (Riedel)
• Unknown etiology; associated with systemic fibrosis.
• Silent/postpartum thyroiditis
• Autoimmune mechanism, often after delivery.

Pathogenesis

• Acute thyroiditis
• Infection spreads to thyroid → acute inflammation → neutrophil infiltration → abscess formation (rare).
• Subacute (De Quervain) thyroiditis
• Viral infection triggers cytotoxic T cell-mediated damage to follicular cells.
• Release of preformed thyroid hormones → transient hyperthyroidism.
• After depletion → hypothyroid phase, followed by recovery.
• Hashimoto thyroiditis
• Autoimmune reaction → lymphocyte and plasma cell infiltration → destruction of thyroid follicles.
• Fibrosis and atrophy over time → permanent hypothyroidism.
• Riedel thyroiditis
• Extensive fibrosis replaces thyroid tissue.
• May extend to surrounding neck structures → compressive symptoms.

Clinical manifestations

• Acute thyroiditis
• Sudden onset neck pain and tenderness.
• Fever, systemic signs of infection.
• Swelling, erythema over thyroid.
• Subacute (De Quervain) thyroiditis
• Painful, tender, enlarged thyroid ("painful thyroiditis").
• Fever, malaise.
• Initial hyperthyroid symptoms: palpitations, heat intolerance, anxiety.
• Later possible transient hypothyroid symptoms.
• Hashimoto thyroiditis
• Painless, firm, diffusely enlarged thyroid ("goiter").
• Symptoms of hypothyroidism:
• Fatigue, weight gain, cold intolerance, constipation.
• Possible transient hyperthyroid phase ("Hashitoxicosis") early on.
• Riedel thyroiditis
• Hard, "woody" thyroid mass.
• Local compressive symptoms:
• Dysphagia, hoarseness, dyspnea.
• Silent/postpartum thyroiditis
• Painless thyroid enlargement.
• Mild hyperthyroid symptoms initially → hypothyroid phase → recovery in most cases.