Primary Hypothyroidism Causes

[Achill Baldwin]

Authordisclosure: Birte Nygaard declares that she has received payment from MERCK-Sorono during 2012 as invited speaker on two occasions, and for writing an overview on the topic of the use of L-T4 + L-T3 in the treatment of hypothyroidism.

Primary hypothyroidism is defined as low levels of blood thyroid hormone due to destruction of the thyroid gland. This destruction is usually caused by autoimmunity or an intervention such as surgery, radioiodine, or radiation.

It can be classified as clinical (overt) when diagnosed by characteristic clinical features, raised levels of thyroid-stimulating hormone (TSH), and reduced levels of thyroxine (T4); or subclinical when serum TSH is raised, but serum T4 is normal, and there are no symptoms of thyroid dysfunction.

Hypothyroidism is characterized by low levels of blood thyroid hormone. Clinical (overt) hypothyroidism is diagnosed on the basis of characteristic clinical features (e.g., mental slowing, depression, dementia, weight gain, constipation, dry skin, hair loss, cold intolerance, hoarse voice, irregular menstruation, infertility, muscle stiffness and pain, bradycardia, hypercholesterolemia), a serum TSH above the reference range, and T4 (and/or triiodothyronine [T3]) below the reference range. A number of guidelines quote serum TSH of 5 to 10 mU per L as mild hypothyroidism, and greater than 10 mU per L as severe hypothyroidism. Subclinical hypothyroidism is a biochemical diagnosis with findings of a serum TSH above the reference range and serum T4 (and/or T3) within the reference range.

Primary hypothyroidism occurs after destruction of the thyroid gland because of autoimmunity (the most common cause) or medical intervention such as surgery, radioiodine, or radiation. Secondary hypothyroidism occurs after pituitary or hypothalamic damage and is caused by insufficient production due to pituitary or hypothalamic hypofunction. Secondary hypothyroidism is not covered in this review. Euthyroid sick syndrome is diagnosed when T3 levels are low, serum T4 is low, and TSH levels are normal or low. Euthyroid sick syndrome is not covered in this review.

Hypothyroidism is more common in women than in men (in the United Kingdom, female-to-male ratio of 6:1). One study (2,779 persons in the United Kingdom with a median age of 58 years) found that the incidence of clinical (overt) hypothyroidism was 40 in 10,000 women per year and six in 10,000 men per year. The prevalence was 9.3% in women and 1.3% in men. In areas with high iodine intake, the incidence of hypothyroidism can be higher than in areas with normal or low iodine intake. In Denmark, where there is moderate iodine insufficiency, the overall incidence of hypothyroidism is 1.4 per 10,000 per year, increasing to eight per 10,000 per year in persons older than 70 years. The incidence of subclinical hypothyroidism increases with age. Up to 10% of women older than 60 years have subclinical hypothyroidism (evaluated from data from the Netherlands and United States).

Primary thyroid gland failure can occur as a result of chronic autoimmune thyroiditis, radioactive iodine treatment, or thyroidectomy. Other causes include drug adverse effects (e.g., amiodarone, lithium), transient hypothyroidism due to silent thyroiditis, subacute thyroiditis, or postnatal thyroiditis.

Subclinical hypothyroidism is associated with depression. Persons with subclinical hypothyroidism may have depression that is refractory to antidepressant drugs and thyroid hormone alone. Memory impairment, hysteria, anxiety, somatic complaints, and depressive features without depression have been described in persons with subclinical hypothyroidism.

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Dr. Marina Basina is an ABMS board certified endocrinologist specializing in diabetes mellitus type 1 and 2, diabetes technology, thyroid nodules, and thyroid cancer. She is currently a clinical associate professor at Stanford University School of Medicine and is a medical director of inpatient diabetes at Stanford Hospital.

Adam Felman is an Editor for Medical News Today and Greatist. Outside of work, he is a hearing impaired musician, producer, and rapper who gigs globally. Adam also owns every Nic Cage movie and has a one-eyed hedgehog called Philip K. Prick.

The symptoms of primary hypothyroidism can range in severity from mild to severe. Symptoms may include tiredness, constipation, weight gain, and depression. Medications that replace thyroid hormones can help reduce or resolve these symptoms in most cases.

Primary hypothyroidism is a more common form of hypothyroidism. This condition occurs after damage to the thyroid gland occurs. This damage may happen as a result of an autoimmune condition, or it may happen following a medical procedure such as surgery or radiation.

The thyroid is a gland located at the front of the throat. This gland produces hormones that are crucial for typical body functions. Thyroid hormones are especially important for supporting metabolic processes.

Metabolic processes in the brain are important for supporting cognitive function and mental health. Primary hypothyroidism disrupts metabolic processes. This may lead to mental health effects such as depression.

In order to make thyroid hormones, the thyroid gland requires iodine. This mineral occurs naturally in foods such as fish, eggs, dairy products, and iodized salt. Certain dietary supplements also contain this important mineral.

Females have an overall higher risk of developing iodine deficiency. Taking iodine supplements can help treat this deficiency and prevent further health complications. A person can speak with a doctor to learn more about helping to prevent or treat iodine deficiency.

Individuals with chronic autoimmune thyroiditis produce higher levels of antithyroid antibodies. These antibodies may harm the thyroid gland in certain cases. In time, this damage can lead to primary hypothyroidism.

To diagnose primary hypothyroidism, a doctor may begin with a physical exam. During this exam, they will determine whether an individual is experiencing symptoms of this condition. These symptoms can include fatigue, constipation, dry skin, and mood changes.

TSH is an important hormone because it instructs the thyroid on how much thyroid hormone to produce. When the thyroid does not produce enough thyroid hormones, the level of TSH rises. Because of this, a high TSH level may indicate primary hypothyroidism.

The thyroid produces the T3 and T4 hormones. These hormones both help the body expend energy. They are crucial for regulating body temperature, weight, and other functions. Low T3 or T4 levels may be a sign of primary hypothyroidism.

Many people experience symptom relief with levothyroxine, although it may not be suitable for everyone. For instance, the thyroid hormones levothyroxine helps produce can have serious effects on heart function. This means the medication may not be appropriate for those with a heart condition.

Primary hypothyroidism occurs when the thyroid gland cannot produce enough thyroid hormones. Secondary hypothyroidism occurs when the thyroid gland functions correctly but the pituitary gland or hypothalamus does not.

In certain cases, primary hypothyroidism can increase the risk of serious health complications. These include heart disease, coronary artery disease, and stroke. Seeking a diagnosis and prompt treatment can help reduce the risk of these and other complications.

Individuals with this condition may experience symptoms such as tiredness, weight gain, constipation, and muscle pain. People experiencing these or other symptoms should visit a healthcare professional for an evaluation.

Congenital hypothyroidism is a partial or complete loss of function of the thyroid gland (hypothyroidism) that affects infants from birth (congenital). The thyroid gland is a butterfly-shaped tissue in the lower neck. It makes iodine-containing hormones that play an important role in regulating growth, brain development, and the rate of chemical reactions in the body (metabolism). People with congenital hypothyroidism have lower-than-normal levels of these important hormones.

Congenital hypothyroidism occurs when the thyroid gland fails to develop or function properly. In 80 to 85 percent of cases, the thyroid gland is absent, severely reduced in size (hypoplastic), or abnormally located. These cases are classified as thyroid dysgenesis. In the remainder of cases, a normal-sized or enlarged thyroid gland (goiter) is present, but production of thyroid hormones is decreased or absent. Most of these cases occur when one of several steps in the hormone synthesis process is impaired; these cases are classified as thyroid dyshormonogenesis. Less commonly, reduction or absence of thyroid hormone production is caused by impaired stimulation of the production process (which is normally done by a structure at the base of the brain called the pituitary gland), even though the process itself is unimpaired. These cases are classified as central (or pituitary) hypothyroidism.

Signs and symptoms of congenital hypothyroidism result from the shortage of thyroid hormones. Affected babies may show no features of the condition, although some babies with congenital hypothyroidism are less active and sleep more than normal. They may have difficulty feeding and experience constipation. If untreated, congenital hypothyroidism can lead to intellectual disability and slow growth. In the United States and many other countries, all hospitals test newborns for congenital hypothyroidism. If treatment begins in the first two weeks after birth, infants usually develop normally.

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