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Hypothyroidism – Definition, Pathophysiology, and Symptoms.

Definition

Hypothyroidism – also called underactive thyroid – is the most common thyroid disorder. It happens when your thyroid gland doesn’t produce enough thyroid hormone, which is essential because thyroid hormone helps regulate important body processes, such as your metabolism. But with low thyroid function, these body processes slow down.

Pathophysiology

The hormones produced by the thyroid gland are T3 and T4. These hormones have an action on almost all parts of the body. The secretion of these hormones is regulated by TSH or thyroid stimulating hormone that is secreted by the pituitary gland. The secretion of thyroid hormone occurs only from this particular gland. The presence of iodine and amino acid tyrosine are a must for the production of thyroid hormones. Hypothyroidism and low levels of the thyroid hormones can occur if there is a deficiency of iodine for thyroid or thyroid stimulating hormone (TSH).

The hypothalamus of the brain secretes TRH thyroid releasing hormone which acts on the pituitary gland and initiates the release of TSH or thyroid stimulating hormone. TSH then acts directly on the thyroid gland to release thyroid hormones T3 and T4. The normal functioning of the thyroid (healthy thyroid) is regulated by negative feedback mechanism where the levels of thyroid hormones increase or decrease under the influence of TSH.

Causes

Risk factors of Hypothyroidism

Signs and Symptoms in adults

Women who are over age 60, as well as men who are aging, should look out for these potential symptoms of hypothyroidism:

Signs and symptoms in Children and teen

Symptoms of hypothyroidism in children and teens are similar to symptoms in adults and can include:

Signs and Symptoms in Infants

Symptoms of hypothyroidism in infants may include:

Complications

Diagnosis and test

Medical evaluation

Your doctor will complete a thorough physical exam and medical history. They’ll check for physical signs of hypothyroidism, including:

In addition, your doctor will ask you to report any symptoms you’ve been experiencing, such as fatigue, depression, constipation, or feeling constantly cold.

Blood test

There are several types of blood tests – the most definitive one is called the TSH test (thyroid-stimulating hormone). However, in some cases, physicians may refer to the free thyroxine or T4, free T4 index, or total T4 to aid in the diagnosis.

TSH Test

A thyroid-stimulating hormone or TSH is a blood test that measures the amount of T4 (thyroxine) that the thyroid is being signaled to make. If you have an abnormally high level of TSH, it could mean you have hypothyroidism. 0.4 mU/L to 4.0 mU/L is considered the reference range (there may be a slight variation depending on the laboratory), TSH >4.0/mU/L with a low T4 level indicates hypothyroidism.

T4 (thyroxine) Test

The thyroid gland produces T4 (thyroxine). The free T4 and the free T4 index are blood tests that, in combination with a TSH test, can let your physician know how your thyroid is functioning.

Anti-thyroid Microsomal Antibodies Testing

A third hypothyroid test is for anti-thyroid microsomal antibodies—anti-thyroid peroxidase (anti-TPO). These antibodies, which are produced by the immune system, may attack thyroid cells. If a blood test determines their presence, it shows that there has been thyroid damage which could potentially lead to hypothyroidism.

Differentiation of Hypothyroidism

Primary hypothyroidism

Primary hypothyroidism is due to disease in the thyroid; thyroid-stimulating hormone (TSH) is increased. The most common cause is autoimmune. It usually results from Hashimoto thyroiditis and is often associated with a firm goiter or, later in the disease process, with a shrunken fibrotic thyroid with little or no function. The 2nd most common cause is post-therapeutic hypothyroidism, especially after radioactive iodine therapy or surgery for hyperthyroidism or goiter.

Secondary hypothyroidism

Secondary hypothyroidism occurs when the hypothalamus produces an insufficient thyrotropin-releasing hormone (TRH) or the pituitary produces insufficient TSH. Sometimes, deficient TSH secretion due to deficient TRH secretion is termed tertiary hypothyroidism.

Subclinical hypothyroidism

Subclinical hypothyroidism is elevated serum TSH in patients with absent or minimal symptoms of hypothyroidism and normal serum levels of free T4. Subclinical thyroid dysfunction is relatively common; it occurs in more than 15% of elderly women and 10% of elderly men, particularly in those with underlying Hashimoto thyroiditis.

Treatment and medication

Medications

Hypothyroidism is a lifelong condition. For many people, medication reduces or alleviates symptoms.

Thyroid Hormone Replacement Therapy

The main goal is to compensate for the lack of hormone secreted by the thyroid gland. In most cases, an affected individual will take a daily dose of T4 (or T3 and T4) in a pill taken orally. But it’s important to understand that every patient’s therapy may be different.

There is no cookie-cutter dosage or treatment plan when it comes to thyroid hormone replacement therapy. How the body absorbs the hormones, along with the number of hormones needed to help the body function properly is very varied.

Prevention of Hypothyroidism

Natural remedies

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