Hashimoto disease is the most common form of autoimmune thyroiditis and the leading cause of hypothyroidism in the United States. Although currently thought to be due to chronic autoimmune-mediated lymphocytic inflammation of the thyroid tissue, the exact pathophysiology remains unclear. Patients are initially asymptomatic or hyperthyroid, progressing to hypothyroidism as the organ parenchyma is destroyed. Diagnosis is based on a combination of specific antibodies, thyroid function tests, and sonography of the thyroid. Treatment involves lifelong hormone replacement therapy with levothyroxine (L-thyroxine).
- Sex: ♀ > ♂ (7:1)
- Age of onset: occurs in all age groups, most prevalent in women aged 30–50 years
Epidemiological data refers to the US, unless otherwise specified.
- Unknown etiology: Genetic and environmental factors likely play a role.
- Immunological mechanisms
- Associations: increased risk for non-Hodgkin lymphoma (usually originating from B cells) and autoimmune diseases (e.g., type 1 diabetes, SLE, Graves disease, Addison disease) 
Subtypes and variants
- Thyroid metabolism 
- Antibody detection
- Other laboratory tests
- Fine-needle aspiration: to exclude malignancy or lymphoma, especially in cases of rapid goiter growth 
- Radioactive iodine uptake test (RIUT): Radioactive iodine uptake is variable, often patchy and irregular with either an increase or decrease in 99mTc uptake. There is ↓ absorption of radioactive technetium (↓ 99mTc uptake) in the thyroid during transient hyperthyroidism
- See “Differential diagnoses of hypothyroidism” and “ .”
- de Quervain thyroiditis) ( 
- Diffuse toxic goiter/
- Nontoxic/multinodular goiter
Riedel thyroiditis (Riedel struma) 
- Rare, special form of autoimmune thyroiditis 
- Characterized by inflammatory infiltration and fibrosclerotic changes of thyroid tissue 
- Part of the IgG4-related disease spectrum, which includes conditions sharing histopathological features of fibrosclerosis in different organs (e.g. sclerosing sialadenitis, retroperitoneal fibrosis, autoimmune pancreatitis, aortitis, etc.)
- Goiter 
- Approx. 30% of affected individuals have hypothyroidism. 
- Surgery may be necessary due to compression.
Acute suppurative thyroiditis
- Definition: extremely rare bacterial infection of the thyroid gland
- Symptoms/clinical features: acute febrile course with tenderness
- Diagnosis: ultrasound
- Treatment: administration of broad-spectrum antibiotics (e.g., clindamycin or amoxicillin with clavulanate); in the case of abscess formation, opening of the abscess and culture of the abscess contents in addition to an antibiogram
- Complications: mediastinitis
The differential diagnoses listed here are not exhaustive.
- Levothyroxine (T4) replacement therapy
- Life-long monitoring