Slow Thyroid (Underactive Gland, Hypothyroidism)

The thyroid gland is the main regulator if the body’s metabolism. By the action of its thyroid hormones, thyroxine (T4) and triiodothyronine), the thyroid gland is able to stimulate metabolic activity, prompting the cells to take up more glucose from the bloodstream and break it down to yield energy. In the process, proteins are synthesized and lipids (fats) from the blood and adipose tissue (fat tissue) are used up. The activity of the thyroid gland is regulated by the pituitary gland. Thyroid-stimulating hormone (TSH) from the anterior pituitary is secreted in response to thyrotropin-releasing hormone (TRH) from the hypothalamus. This mechanism keeps the thyroid activity in check and allows for a rise in metabolic rate during activity and a drop during low energy states like sleep.

What is a slow thyroid gland?

A ‘slow thyroid‘ is a common term for an underactive thyroid gland or hypothyroidism. It may involve diseases affecting the thyroid gland itself, or those that compromise the regulating mechanism in the anterior pituitary and/or hypothalamus.

What is hypothyroidism?

Hypothyroidism is the hypofunctioning (‘under-functioning’) of the thyroid gland leading to a deficiency of thyroid hormones, thyroxine (T4) and triiodothyronine (T3). Hypothyroidism can be labeled primary when the disease process is isolated to the thyroid gland or secondary when it involves the pituitary and/or hypothalamus with an otherwise normal thyroid gland. Most cases are primary hypothyroidism and often is a result of autoimmune diseases.

Hypothyroidism may be associated with enlargement of the thyroid gland (goiter) although this is not present in every case. When hypothyroidism is seen in infants or in early childhood, it is termed cretinism. It may also be seen with maternal hypothyroidism. Myxedema refers to hypothyroidism seen in the older child or adult. Overall hypothyroidism is seen more frequently in females than males.

Causes of Hypothyroidism

Most cases of hypothyroidism are primary meaning that the pathology involves the thyroid gland. Simply primary hypothyroidism can be classified as autoimmune, acquired and congenital. Some cases of hypothyroidism is due to unknown causes (idiopathic).


This is the most common cause of hypothyroidism. Antibodies either causer inflammation of the thyroid gland (thyroiditis) or block the TSH receptors on the thyroid gland.

Hashimoto’s thyroiditis is by far the most common cause in developed countries.


Acquired causes may occur at any time in life and these days it is more often due to iatrogenic factors – hypothyroidism causes by medical treatment or diagnostic investigation. Some cases, like with viral infections, there is initially hyperthyroidism (overactive thyroid gland) followed by hypothyroidism (underactivity).

  • Drugs used to treat hyperthyroidism (carbimazole), depression (lithium), arrhythmia (amiodarone), antibiotics (p-aminosalicylic acid)
  • Thyroidectomy (surgical removal of the thyroid gland)
  • Radioactive iodine
  • Iodine deficiency
  • Subacute (de Quervain’s) thyroiditis – possibly viral infection


These are causes present from birth often due to inherited diseases.This may be seen as hypothyroidism in infants or only becoming evident later on in early childhood.

  • Endemic iodine deficiency
  • Dyshormonogenesis is a genetic defect that disturbs the multi-step process for thyroid hormone production.
  • Thyroid aplasia – failure of the thyroid gland to develop or grow.


Secondary causes is almost always due to a deficiency of thyroid-stimulating hormone (TSH) as a result of hypopituitarism (underactive pituitary gland).

Signs and Symptoms of an Underactive Thyroid Gland

The signs and symptoms of hypothyroidism depend on the severity of the thyroid hormone deficiency and duration of the condition.

  • Fatigue
  • Moderate weight gain
  • Intolerance to cold

Other common clinical features include :

  • Depression
  • Constipation
  • Goiter (thyroid gland enlargement)
  • Dry skin
  • Thinning hair – hair is coarse and brittle
  • High cholesterol levels
  • Puffy face
  • Menstrual disturbances
  • Paleness
  • Puffy face
  • Droopy eyelids
  • Leg swelling

Infants and Young Children

The thyroid hormones also regulate growth and therefore development will be retarded to some degree in congenital hypothyroidism or prolonged hypothyroidism in young children. The clinical features of cretinism include :

  • Short stature
  • Mental retardation
  • Coarse facial features
  • Protruding tongue

Older Children and Adults

These clinical features are seen with prolonged hypothyroidism and develop gradually over years. Older children may also have some features of cretinism.

  • Physically and mentally slow
  • Poor memory
  • Hoarse voice
  • Shortness of breath
  • Enlargement of the tongue
  • Non-pitting edema (pretibial myxedema)

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