What is Hashimoto's thyroiditis?

What is Hashimoto's Thyroiditis?

Hashimoto's thyroiditis is a chronic autoimmune disease where the immune system attacks and destroys the thyroid gland through lymphocytic infiltration, making it the most common cause of hypothyroidism in iodine-sufficient regions and affecting women 7-10 times more frequently than men. 1, 2, 3

Pathophysiology and Mechanism

• The disease results from a loss of immunological tolerance triggered by a combination of genetic susceptibility and environmental factors, leading to autoimmune destruction of thyroid tissue 3, 4
• Both cellular (T-cell mediated) and humoral (antibody-mediated) immunity drive the pathologic process 5, 4
• Histologically, the thyroid shows lymphoplasmacytic infiltration with lymphoid follicle formation, germinal centers, parenchymal atrophy, and eventual fibrosis 3, 4
• The progressive destruction causes the thyroid gland to shrink and ultimately leads to hypothyroidism in most cases 6

Clinical Presentation and Diagnosis

• Patients typically present with symptoms of hypothyroidism including unexplained fatigue, weight gain, hair loss, cold intolerance, constipation, and depression 1
• Diagnosis requires TSH testing as the initial screening test, followed by free T4 measurement if TSH is abnormal 1, 2
• Positive serum antibodies against thyroid peroxidase (TPO) and thyroglobulin confirm the autoimmune etiology 1, 4
• Multiple tests over 3-6 months should confirm persistently abnormal findings before initiating treatment 1

Associated Autoimmune and Systemic Conditions

A critical pitfall is failing to recognize that Hashimoto's thyroiditis frequently coexists with other autoimmune disorders, requiring broader clinical vigilance:

• Autoimmune thyroid disease is the most common concurrent autoimmune condition in various patient populations, accounting for 10-23% of associated disorders 1
• Type 1 diabetes mellitus commonly coexists with Hashimoto's thyroiditis 1, 2
• Systemic lupus erythematosus occurs in approximately 2.2-2.8% of patients 1, 2
• Other associations include rheumatoid arthritis, Sjögren syndrome, and inflammatory bowel disease 1
• Metabolic abnormalities including insulin resistance and type 2 diabetes are also associated 2

Important Clinical Considerations

• Many patients with Hashimoto's thyroiditis experience persistent symptoms and reduced quality of life even when thyroid function tests are normal (euthyroid state) 2, 7
• These euthyroid patients may still suffer from neuropsychological deficits, decreased cardiac performance, gastrointestinal disorders, fibromyalgia, and reproductive issues 7
• The disease can progress through phases: some patients initially experience hyperthyroidism (Hashitoxicosis) before developing hypothyroidism 1
• A potential relationship exists between Hashimoto's thyroiditis and papillary thyroid cancer, though this correlation requires further investigation 3, 4

Treatment Approach

• The primary treatment for hypothyroidism resulting from Hashimoto's thyroiditis is daily oral levothyroxine (synthetic T4) replacement therapy 8, 3
• When both adrenal insufficiency and hypothyroidism are present, steroids must always be started before thyroid hormone to prevent adrenal crisis 1
• Regular monitoring of thyroid function during levothyroxine therapy is required to maintain optimal dosing 2
• Liothyronine (T3) can be used as an alternative in patients allergic to desiccated thyroid or thyroid extract 8
• Thyroid function should be monitored at 2-4 month intervals during treatment and regularly for 1 year after any treatment changes 1