Hypothyroidism (Underactive Thyroid Gland)

Definition

Hypothyroidism is a condition caused by insufficient levels of thyroid hormones in the bloodstream. There hormones are required for the proper metabolic functioning of the body, its growth and development. Thyroid hormones, T3 and T4, are produced in the thyroid gland, which is situated in the neck. The gland may be diseased, have insufficient constituents to produce thyroid hormones or may not be adequately stimulated to secrete the hormones. It can affect people of all ages but it is most common in middle aged and old women.

Hypopthyroidism can therefore be defined as primary when it is the thyroid gland that is diseased and not producing sufficient thyroid hormones. It can alternatively be defined as secondary when the thyroid gland is healthy and able to produce sufficient thyroid hormones but is not stimulated appropriately or has insufficient constituents to produce thyroid hormone. In these cases the problem does not lie in the thyroid gland but in outside factors that influence the gland. Hypothyroidism tends to cause very obvious symptoms and is therefore easily detectable. It is also easily treated and managed with regular intake of synthetic thyroid hormones.

Symptoms

Early symptoms usually include sluggishness and fatigue which may go unnoticed. As the disease develops these symptoms worsen and other symptoms become evident :

  • Weakness
  • Muscle aches and joint pain
  • Constipation
  • Intolerance to cold
  • Weight gain
  • Dry skin and brittle nails
  • Abnormal menstrual flow or irregular periods
  • Depression
  • High cholesterol level

If untreated, enlargement of the neck may become noticeable. This condition is known as goiter. As hypothyroidism worsens various complications arise that can be fatal. During pregnancy, untreated hypothyroidism can affect the mental and physical growth of the unborn child. When it occurs in infancy or childhood, untreated hypothyroidism can result in abnormal growth and mental retardation.

Causes

The diminished production and secretion of thyroid hormones can occur for several reasons. It is important to note that the thyroid gland is stimulated by the pituitary gland which secretes TSH (thyroid stimulating hormone).  The pituitary gland in turn is controlled by the hypothalamus in the brain.

  • Iodine deficiency.  Iodine is required for the production of the hormone. Lack of iodine in the diet can cause hypothyroidism. This is largely avoided in this day and age as foods are fortified with iodine.
  • Autoimmune diseases. When the body produces antibodies against the thyroid gland, the immune system may attack it and the gland may be unable to produce sufficient thyroid hormones The reasons for this condition are not well understood. It is often seen in a form of thyroid gland dysfunction known as Hashimoto’s thyroiditis.
  • Surgical removal of the thyroid gland, either a large part of it or the entire gland, will lead to hypothyroidism. Resection is done in the treatment of cancer.
  • Medication. In some cases, treatment of hyperthyroidism (condition where excess thyroid hormones are produced) can lead to a decrease in the thyroid hormones below normal levels.Medication for psychiatric disorders containing lithium, radiation therapy for treatment of cancers of the head and neck can also affect thyroid gland activity.
  • Congenital disorders. Some babies are born with an abnormal or absent thyroid gland leading to absence of thyroid hormone
  • Pituitary gland malfunction may result in insufficient TSH to stimulate the thyroid gland which can also be linked to hypothalamic disorders.

Treatment

Diagnosis of this condition is done by measuring the levels of TSH, T3 and T4 in the blood. If pituitary function is normal then TSH levels might be normal or higher whereas T3 and/or T4 levels would be low. Administration of synthetic thyroid hormone, levothyroxine, is the usual approach for treating hypothyroidism. Since this is a replacement of the normal hormone it is usually needed life-long. Synthetic thyroid hormones will often alleviate all of the symptoms within a couple of weeks. Regular monitoring and adjustment of the synthetic thyroid hormone dosage may be required.

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