Hashimoto's thyroiditis

Hashimoto's thyroiditis
Name	Hashimoto's thyroiditis
Synonyms	Chronic lymphocytic thyroiditis, Hashimoto's disease
Field	Endocrinology, Immunology
Symptoms	Fatigue, weight gain, cold intolerance, depression
Complications	Myxedema, Goiter, increased risk of Non-Hodgkin lymphoma
Onset	Most common in middle age
Duration	Lifelong
Causes	Autoimmune
Risks	Female sex, family history, other autoimmune diseases
Diagnosis	Blood tests (TSH, anti-TPO antibodies), ultrasound
Differential	Graves' disease, Subacute thyroiditis, Drug-induced thyroiditis
Prevention	None known
Treatment	Levothyroxine
Prognosis	Excellent with treatment
Frequency	~5% of population

Hashimoto's thyroiditis. It is a chronic autoimmune disorder in which the immune system attacks the thyroid gland, leading to progressive inflammation and eventual hypothyroidism. First described in 1912 by Japanese physician Hakaru Hashimoto in Germany, it represents the most common cause of hypothyroidism in areas with sufficient iodine intake. The condition is characterized by the presence of specific autoantibodies and typically requires lifelong management with thyroid hormone replacement.

Signs and symptoms

Initial stages are often asymptomatic, but as thyroid destruction progresses, symptoms of hypothyroidism emerge. Common manifestations include profound fatigue, unexplained weight gain, cold intolerance, dry skin, constipation, and depression. Patients may develop a painless goiter or notice swelling in the neck due to lymphocytic infiltration. Advanced disease can lead to bradycardia, hoarseness, and myxedema, a severe form of hypothyroidism. Associated autoimmune conditions like vitiligo, rheumatoid arthritis, or celiac disease may present with their own symptomatology.

Causes and risk factors

The exact cause involves a complex interplay of genetic predisposition and environmental triggers. Strong familial clustering is observed, with links to specific human leukocyte antigen alleles like HLA-DR5. The primary environmental risk factor is excessive iodine intake, which may exacerbate the autoimmune process. It is significantly more common in women, with a female-to-male ratio of about 10:1. Other major risk factors include a personal or family history of autoimmune disorders such as type 1 diabetes, Addison's disease, or pernicious anemia. Exposure to ionizing radiation, as seen in survivors of the Chernobyl disaster, is also a recognized risk factor.

Pathophysiology

The pathophysiology centers on a breakdown in immune tolerance to thyroid antigens. Cytotoxic T lymphocytes and autoantibodies, primarily against thyroid peroxidase and thyroglobulin, mediate glandular destruction. This results in a dense infiltration of the thyroid by lymphocytes, forming germinal centers and progressive fibrosis. The ongoing inflammatory process, termed lymphocytic thyroiditis, impairs the gland's ability to produce hormones thyroxine and triiodothyronine. This leads to elevated thyroid-stimulating hormone from the pituitary gland in a failed compensatory feedback loop, further stimulating the already damaged thyroid.

Diagnosis

Diagnosis is confirmed through serological testing and clinical assessment. Key laboratory findings include elevated serum thyroid-stimulating hormone and low free thyroxine levels. The presence of high titers of anti-thyroid peroxidase antibodies is highly specific. Ultrasonography of the thyroid typically reveals a diffusely hypoechoic and heterogeneous gland, sometimes with pseudonodules. In ambiguous cases, a fine-needle aspiration biopsy may be performed, showing an abundance of lymphocytes and Hurthle cells. Differential diagnosis includes other forms of thyroiditis like de Quervain's thyroiditis and Graves' disease.

Treatment and management

The standard treatment is daily oral administration of synthetic levothyroxine to normalize thyroid-stimulating hormone levels. Dosage is titrated based on periodic blood tests, with special consideration required during pregnancy or when initiating medications like estrogen or proton-pump inhibitors. Treatment is usually lifelong. Surgical intervention, or thyroidectomy, is rarely indicated but may be necessary for a large obstructive goiter or suspicion of malignancy like papillary thyroid carcinoma. Patients are often monitored by an endocrinologist, and concurrent management of associated conditions like vitamin B12 deficiency is important.

Epidemiology

It is the most prevalent autoimmune disease, affecting approximately 5% of the general population in iodine-sufficient regions. Incidence peaks in middle age, between 30 and 50 years, but can occur at any age, including in children as juvenile autoimmune thyroiditis. There is significant geographic variation, with higher prevalence reported in countries like the United States and Japan. The incidence appears to be increasing globally, potentially linked to environmental factors and improved diagnostic techniques. It is a leading cause of hypothyroidism in the United States, far surpassing causes like iodine deficiency.

Category:Autoimmune diseases Category:Endocrinology Category:Thyroid disease