Hashimoto’s disease and hypothyroidism are often discussed together, but they represent two different concepts in thyroid health. Hypothyroidism describes the physical state of having low thyroid hormone levels, which is a common condition. Hashimoto’s thyroiditis is the most frequent cause of that low hormone state in the United States, but it is fundamentally an autoimmune disease. Hypothyroidism is the result, while Hashimoto’s is the specific underlying problem. Understanding this distinction is necessary for proper diagnosis and management.
Defining the State of Low Thyroid Function
Hypothyroidism is a condition defined by the insufficient production of thyroid hormones by the thyroid gland. This butterfly-shaped gland, located in the neck, is responsible for synthesizing thyroxine (T4) and triiodothyronine (T3). These two hormones regulate nearly every cell and tissue in the body.
The primary role of T3 and T4 is to control the body’s metabolism, including how food is converted into energy. Low levels of these hormones lead to a general slowdown of bodily functions, affecting energy levels, heart rate, and internal temperature. When the thyroid gland fails to produce enough T4 and T3, the result is the clinical state known as hypothyroidism, regardless of what caused the failure. Other potential causes of this hormone deficiency, besides Hashimoto’s, can include surgical removal of the thyroid or certain medications.
The Underlying Autoimmune Process
Hashimoto’s thyroiditis is a specific autoimmune disorder. In this condition, the body’s immune system mistakenly identifies the thyroid gland’s cells as foreign invaders. This leads to a chronic attack mediated by immune cells, primarily lymphocytes, which results in inflammation and gradual destruction of the thyroid tissue.
The damage caused by this immune response diminishes the thyroid’s ability to produce T4 and T3 hormones over time. It is this progressive destruction that eventually leads to the development of hypothyroidism. A person can have Hashimoto’s, confirmed by specific testing, for years before the damage is severe enough to cause clinically low thyroid hormone levels.
How Doctors Tell Them Apart
The distinction between the two conditions is determined by blood tests. Hypothyroidism is diagnosed by measuring the functional status of the thyroid gland. The primary marker is Thyroid-Stimulating Hormone (TSH), which is elevated when the thyroid is underactive because the pituitary gland is attempting to stimulate the failing gland.
Doctors also measure free thyroxine (Free T4) levels, which are often low in overt hypothyroidism. Hashimoto’s, in contrast, is identified by specialized tests that look for the presence of specific antibodies in the blood. The most common antibodies tested are Thyroid Peroxidase Antibodies (TPOAb) and Thyroglobulin Antibodies (TgAb).
A positive result for TPOAb or TgAb indicates the presence of the autoimmune process, confirming a diagnosis of Hashimoto’s thyroiditis. It is possible to have elevated antibodies (Hashimoto’s) with normal TSH and T4 levels, meaning the person has the autoimmune condition but has not yet developed hypothyroidism. Conversely, a person with low T4 and high TSH (hypothyroidism) but negative antibodies has hypothyroidism due to a non-Hashimoto’s cause.
Management Strategies and Monitoring
Management of Hashimoto’s disease, once it progresses to hypothyroidism, centers on treating the hormone deficiency. This is achieved through hormone replacement therapy, most commonly with the synthetic T4 hormone, levothyroxine. The goal of this treatment is to restore the circulating levels of T4 and T3 to the normal range, which stabilizes the TSH level.
Monitoring patients with Hashimoto’s involves considerations beyond regulating TSH and T4. Individuals with Hashimoto’s often have a higher risk of developing other autoimmune disorders, such as Type 1 diabetes or pernicious anemia. While antibody levels are not used to adjust the levothyroxine dose, tracking them may offer insight into the activity of the underlying autoimmune disease. The treatment for hypothyroidism is required for life to sustain adequate hormone levels.