Hashimoto thyroiditis is the most common type of autoimmune thyroiditis and the leading cause of hypothyroidism in the United States. Although it is thought to be due to chronic autoimmune-mediated lymphocytic inflammation and destruction of the thyroid tissue, the exact pathophysiology remains unclear. Patients may initially be asymptomatic or show signs of thyrotoxicosis, progressing to hypothyroidism as the organ parenchyma is destroyed. Diagnosis is based on a combination of clinical features, thyroid antibodies, and thyroid function tests. Additional studies (e.g., ultrasound, fine-needle aspiration) may be obtained to rule out alternative conditions and may support the diagnosis. Management consists of lifelong monitoring and, in most cases, hormone replacement therapy with levothyroxine.
- 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
- Primarily asymptomatic
- Goiter: nontender or painless, rubbery thyroid with moderate and symmetrical enlargement 
- Hashitoxicosis may occur: transient thyrotoxicosis due to follicular rupture of hormone-containing thyroid tissue that manifests with signs of hyperthyroidism (e.g., irritability, heat intolerance, diarrhea)
Subtypes and variants
- Obtain for all patients:
- Thyroid antibodies to confirm the diagnosis
- In patients with thyroid nodules: Obtain a . or suspected
- Consider additional studies to rule out differential diagnoses.
Laboratory studies 
- Thyroid function tests (TFTs)
- Thyroid antibodies 
- Other laboratory findings 
- Fine-needle aspiration
- Radioactive iodine uptake test (RIUT) 
- 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.
Lifelong oral levothyroxine replacement is required in most patients with Hashimoto thyroiditis.
- Overt hypothyroidism
- Subclinical hypothyroidism: Consider low-dose levothyroxine. 
- Hashitoxicosis: with ß-blockers 
- Goiter: may be considered in patients with obstructive symptoms or for cosmetic reasons. 
- For all phases (including euthyroidism) 
- After levothyroxine initiation or dosage change