Hashimoto's thyroiditis, also known as chronic lymphocytic thyroiditis, is an autoimmune condition in which the patient's immune system attacks the thyroid leading to chronic inflammation of the thyroid gland. The thyroid is a butterfly-shaped gland in the lower neck that makes hormones that help regulate growth and development, body temperature, heart rate, and weight. Chronic inflammation of the thyroid eventually leads to an impaired ability of the thyroid gland to produce thyroid hormones, such as T3 and T4, leading to a gradual decline in function and ultimately to hypothyroidism.
Symptoms
Symptoms of Hashimoto's come on gradually as the condition progresses. Patients usually have an increased level of thyroid stimulating hormone (TSH) with anti-thyroglobulin (TG) and/or anti-thyroid peroxidase (TPO) antibodies present positively in their blood work. One of the first signs of Hashimoto's is the enlargement of the thyroid with a sign of swelling at the front of the throat called a goiter. This occurs due to the slow and chronic cell damage from inflammation that leads to the development of an enlarged thyroid. Hashimoto's symptoms may include fatigue, weight gain, constipation, increased sensitivity to cold, slowed heart rate, dry skin, depression, muscle aches, and reduced exercise tolerance. These symptoms are associated with reduced thyroid hormones levels.
Pathogenesis
The cause of Hashimoto's is not fully understood but researchers believe it is a combination of genetics and environmental factors. Several genes have been studied as a possible risk factor and other non-genetic factors have also been identified. These include, changes in sex hormones, viral infections, certain medications, exposure to radiation, and excess consumption of iodine.
White blood cells called lymphocytes accumulate in the thyroid and produce antibodies that attack and destroy the cells in the thyroid gland. This lymphoid infiltration of the thyroid gland characterized in Hashimoto's includes both B and T cells. These antibodies typically include thyroid peroxidase and/or thyroglobulin autoantibodies. Once enough cells have become damaged, the thyroid can no longer make enough hormones to regulate body functions.
Autoimmune and the Lymphatic System
The lymphatic system is a major part of the immune system and it plays a key role in the development of autoimmune conditions. Research results have shown that lymphatic dysfunction and the resulting decreased lymphatic circulation can induce symptoms of autoimmune conditions.
Both B cells and T cells are produced in bone marrow, but B cells mature in the spleen and T cells mature in the thymus. Both the spleen and thymus are key organs of the lymphatic system. Lymphatic dysfunction and poor lymph quality may affect the B cells and T cells maturation and cause their loss of self-tolerance.
Using MRI and ultrasound, researchers further examined the role of the lymphatics in patients with autoimmune conditions such as rheumatoid arthritis and have shown that the lymphatic flow and contraction frequency in patients with autoimmune condition such as rheumatoid arthritis have been impaired. Slowed lymphatic circulation may cause an accumulation of excessive cell debris and protein fragments which could cause a loss of self-tolerance of the immune system as well as trigger immune system activation.
Hashimoto's and Liver Disease
The liver also plays an important role in immunological activity. The liver has a much more powerful innate immune capability versus the blood due to its enriched macrophage content and natural killer cells. The liver produces suppressor T cells that control T cell activity. Suppressor T cells, are a subpopulation of T cells that modulate the immune system, maintain tolerance to self-antigens, and prevent autoimmune disease. Research has found that people with Hashimoto's hypothyroidism are at a higher risk of developing fatty liver disease because of the effect of a low thyroid levels on fat metabolism and liver function. Elevated liver enzymes have also been documented in patients with Hashimoto's. Prolonged use of immunosuppressant drugs such as methotrexate can also affect the liver and disrupt liver function. A liver deficiency can result in poorly functioning suppressor T cells and subsequently attribute to autoimmune conditions or the worsening of the Hashimoto's.
