Autoimmune thyroid diseases

Clinical information

Autoimmune thyroid diseases are the most common type of autoimmune diseases. In the blood of the patients, autoantibodies can be detected, which are directed against different thyroid proteins and impair their functioning. Antibodies against thyroid microsomes with the main antigen thyroperoxidase (anti-TPO) and antibodies against thyroglobulin (anti-TG) or the thyroid-stimulating hormone receptor (TRAb) are characteristic of autoimmune thyroid diseases. The most frequent autoimmune thyroid diseases are Graves’ disease and Hashimoto’s thyroiditis. While Graves’ disease is typically associated with hyperthyroidism, Hashimoto’s thyroiditis usually manifests as hypothyroidism.  

Graves’ disease is the most frequent cause of hyperthyroidism in regions with sufficient iodide supply. It often has a sudden onset, with initial symptoms such as palpitations and nervousness. The prevalence is approximately 1.5 %, with women being eight times more likely to be affected than men. Its pathogenesis mainly involves continuous stimulation of TSH receptors through the binding of TRAb. They act as TSHR agonists and lead to increased iodide uptake, resulting in thyroid growth and increased thyroid-hormone synthesis and release. Main symptoms are the development of a struma, tachycardia and endocrine orbitopathy.  

Hashimoto’s thyroiditis affects approximately 2 % of women and 0.2 % of men. In contrast to Graves’ disease, the onset of Hashimoto’s disease is usually clinically inconspicuous and can lead to hypothyroidism after years. The majority of patients develop a struma. Typical symptoms are cold intolerance, constipation and fatigue. The underlying cause of the disease is autoimmune lymphocytic infiltration, which leads to a T-cell-mediated destruction of thyroid tissue and thus to reduced production of the thyroid hormones triiodothyronine (T3) and thyroxine (T4) in the long term. The antibodies characteristic of Hashimoto’s thyroiditis are anti-TPO and anti-TG.  

Postpartum thyroiditis (PPT) is a de novo autoimmune disease that occurs in approximately 5 % to 9 % of women within one year of delivery and is associated with high titers of anti-TPO and/or anti-TG. The risk of developing the disease is particularly high in mothers who already had thyroid antibodies before pregnancy or who have type 1 diabetes mellitus. The majority of affected women develop transient hypothyroidism. But a hyperthyroid phase may also be followed by a hypothyroid phase or isolated thyrotoxicosis may occur. In 20 % to 40 %, hypothyroidism persists beyond the postpartum period.

Diagnostics

If thyroid disease is suspected, a thyroid function test should be performed to supplement the clinical picture. It involves determining the TSH concentration in the blood. An increased TSH level indicates hypothyroidism and a decreased level hyperthyroidism. Additionally, the levels of the free thyroid hormones fT3 and fT4 should be measured in the blood. For the differentiation of an autoimmune thyroid disease from acute (bacterial) or subacute (non-infectious) thyroiditis or a non-autoimmune dysregulation of thyroid function, the determination of antibodies against thyroid antigens is useful. TRAb are the most important serological markers of Graves’ disease, as they can be detected in almost all untreated patients. Their concentration correlates with disease activity. In mild courses, the TRAb level may be in the normal range. In these cases, detection of anti-TPO can support the diagnosis, as they are found in 90 % and anti-TG in up to 30 % of cases of Graves’ disease. In Hashimoto’s thyroiditis, anti-TPO are found in about 95% of patients, anti-TG in 60 % to 80 % and TRAb in 6 % to 12 %.   

For reliable differential diagnostics, the results for different parameters must be evaluated in the overall context. In addition to serological results, the clinical picture as well as the results of imaging techniques such as sonography or scintigraphy must be taken into account.  

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Autoimmune thyroid diseases