Autoimmune Thyroid Disease: Hashimoto's & Graves' Pathophysiology

Hashimoto's thyroiditis and Graves' disease are the two most common autoimmune thyroid disorders, representing opposite ends of functional spectrum.

Hashimoto's Thyroiditis (Chronic Lymphocytic Thyroiditis)

• Mechanism: CD4⁺ T‑cell‑mediated destruction of thyrocytes; anti‑TPO and anti‑Tg antibodies.
• Course: Gradual follicular loss → hypothyroidism.
• Labs: ↑TSH, ↓Free T4, ↑anti‑TPO (>90%), ↑anti‑Tg.
• Associations: Other autoimmune (celiac, type 1 DM, vitiligo, pernicious anemia).

Graves' Disease

• Mechanism: Thyroid‑stimulating immunoglobulins (TSI/TRAb) bind TSH receptor → constitutive stimulation.
• Course: Hyperthyroidism; may have ophthalmopathy (50%), dermopathy (pretibial myxedema).
• Labs: ↓TSH, ↑Free T4/T3, ↑TRAb, ↑T3/T4 ratio.

Shared Features

• Female predominance (7–10:1).
• Genetic susceptibility (HLA‑DR3, CTLA‑4, PTPN22).
• Environmental triggers: stress, smoking (Graves'), iodine excess, selenium deficiency, infection.

Treatment Overview

• Hashimoto's: Levothyroxine replacement when TSH >10 or symptomatic / TSH 4–10 with antibodies/goiter.
• Graves': Antithyroid drugs (methimazole), radioactive iodine (¹³¹I), or thyroidectomy. Beta‑blockers for symptom control.