Autoimmune Hypothyroidism

Subtypes and Causes

Learn about the subtypes, symptoms, diagnosis, treatment, and disease course in autoimmune hypothyroid disorders.

Classifications of Autoimmune Disease

Autoimmune disorders are classified as systemic, which means that they involve multiple bodily organs and systems, or organ-specific, which means that they primarily target one organ. Autoimmune thyroid disorders can cause hypothyroidism, a condition of diminished thyroid function, or hyperthyroidism, a condition of increased thyroid function. Both types of thyroid dysfunction cause specific symptoms and have specific consequences.

Autoimmune Hypothyroidism Subtypes

Autoimmune hypothyroidism is the most common organ-specific autoimmune disorder. Two specific forms of autoimmune hypothyroidism exist: 1) chronic autoimmune thyroiditis, which is also known as Hashimoto's thyroiditis or Hashimoto's disease, and its variants, postpartum and sporadic thyroiditis, and 2) autoimmune atrophic thyroiditis, which is also known as primary myxedema.

Myxedema

Myxedema is a term referring to the skin changes characterized by pitting and swelling (water-logged appearance) associated with hypothyroidism. Before laboratory tests for thyroid function were developed, most hypothyroid disorders were diagnosed on the basis of goiter and myxedema. The severity of autoimmune hypothyroidism varies ranging from subclinical hypothyroidism, which is described in my 5-21-06 article, to fatal conditions of myxedema coma. This article describes the causes, symptoms, diagnosis and treatment of autoimmune hypothyroidism.

Causes

Autoimmune hypothyroidism is caused by a combination of genetic and environmental factors. That is, people with certain immune and organ-specific genes are predisposed to developing autoimmune thyroid disorders when they're exposed to certain environmental triggers.

Several of these genes and environmental triggers have been identified but genetic tests aren't used outside of research since immune system genes aren't specific; they cause predisposition to several different autoimmune disorders. Environmental triggers include: iodine deficiency, iodine excess, lithium, selenium deficiency, cigarette smoke, sex steroids, trauma, interferon-alpha used in hepatitis C and other disorders, infection with Yersinia and viruses, iodine-rich medications such as amiodarone, and iodine contrast dyes used in imaging tests.

Symptoms

Symptoms vary although patients with Hashimoto's disease and its variants are more likely to develop goiter and patients with atrophic thyroiditis typically have a small firm thyroid gland characterized by fibrous or scar tissue. Because hypothyroidism affects all of the body's organs and systems, a variety of different symptoms can occur. Most patients do not have all of these symptoms, but rather develop a constellation of predominant symptoms that can change over time and with treatment.

Depression is one of the earliest symptoms to occur in hypothyroidism, followed by skin and hair changes. Myxedema is one of the most characteristic symptoms and is associated with accumulations of mucopolysaccharides beneath the skin. These mucin deposits may thicken the tongue, surround the heart, leading to congestive heart failure, and lead to diminished function of virtually any organ. The skin in hypothyroidism is cold, dry and pale and the palms may take on a yellow tinge associated with the inability to properly metabolize vitamin A. This hue may also occur on the soles and the folds on each side of the nose. Hair loss is common and the outer third of the eyebrow is usually sparse. Nails may appear thickened, brittle and grow slowly. 

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