Most common form of autoimmune thyroiditis and the leading cause of hypothyroidism in the United States.- F:M = 7:1

- Associations with HLA-DR3 and DR5, non-Hodgkin's lymphoma or autoimmune diseases

Diagnosis:- Thyroid function tests- Antibody detection: → Anti-TPO antibody (also positive in 70% of patients with Graves disease)→ Anti-Tg antibody positive → Anti-microsomal antibodies- Ultrasound- Fine-needle aspiration: To exclude malignancy or lymphoma

Pathology:- Diffuse lymphocytic infiltration (cytotoxic T lymphocytes) with germinal centers- Follicular cells change into Hurthle cells (oncocytic-metaplastic cells with eosinophilic cytoplasm) - Follicles atrophy- Fibrotic tissue

Treatment:- Levothyroxine (T4) replacement therapy- Life-long monitoring

Complications:- Myxedema coma- Thyroid lymphoma