Underactive Thyroid

Causes of Underactive Thyroid (Hypothyroidism)

Primary Hypothyroidism or Underactive Thyroid can be caused due to several reasons such as follows: chronic active hepatitis: Patients of ulcerative colitis may have concurrent hepatitis C infection.

• Iodine deficiency in food is one of the common causes especially in certain geographic areas of the world.
• Inflammation of the thyroid gland which causes damage or death of the cells of thyroid leading to insufficient production of the hormones is a major cause of Primary hypothyroidism. The main cause of failure of thyroid gland in this manner is by Auto-immune Thyroiditis also known as Hashimoto’s Thyroiditis. In this disorder, the patients own immune system causes an inflammation of the gland.
• Post-thyroidectomy: Surgical removal of the thyroid gland or a nodule for treating hyperthyroidism often makes the patient land up with Hypothyroidism after a few years.
• Post-radiotherapy: Radiotherapy given for hyperthyroidism in order to destroy the hyperactivity of the gland. If larger number of cells are destroyed by the radioactive iodine, the patient may have insufficient hormone production by the remaining cells and this may cause hypothyroidism.

Secondary hypothyroidism is commonly caused by the following:

1. Failure of the pituitary gland to secrete Thyroid Stimulating Hormone (TSH). This may be caused due to:
   • Tumor in the pituitary region
   • Infiltration of the pituitary by inflammatory cells from the immune system
   • Infiltration of the pituitary by foreign substances (such as iron in Hemochromatosis)Hypothalamic dysfunction
   • Risk factors for secondary hypothyroidism include being over 50 years old, being female, and having a history of pituitary or hypothalamic dysfunction.

Symptoms of Underactive Thyroid (Hypothyroidism)

The symptoms of hypothyroidism are frequently missed out and especially in elderly females these are mistaken to be symptoms of menopause. The beginning of the symptoms is often not noted markedly and hence the condition remains under-diagnosed.

Patient may experience few of the following symptoms:

• Fatigue, exhaustion
• Weakness, sluggishness
• Unexplained weight gain or increased difficulty losing weight
• Coarse, dry hair and/or thinning of hair
• Hair loss
• Dry, rough, pale and itchy skin
• Cold intolerance (can’t tolerate the cold like those around you)
• Constipation
• Depression, mood swings
• Irritability
• Memory loss
• Abnormal menstrual cycles, increased menstrual flow
• Decreased libido
• Infertility, miscarriages
• Difficulty in concentrating
• Thinning and/or falling out of sides of eyebrows
• Puffy, swollen face and dull facial expressions
• Hoarse voice and slow speech
• Goiter (swelling of the thyroid gland)
• Non-pitting edema (swelling)
• Pitting edema (swelling) of the feet

Patient may have any kind of combination of the symptoms mentioned above depending on the duration and severity of the condition. Occasionally patient may be asymptomatic or may be having very subtle symptoms.

Diagnosis of Underactive Thyroid (Hypothyroidism)

Diagnosis of hypothyroidism can be established based on the results of tests done to measure the levels of these hormones in the blood. Commonly T4 and TSH in blood are measured. Since hypothyroidism is about deficiency or low levels of thyroid hormones, T4 (and T3) levels in the blood are below normal. TSH levels are high in case of Primary hypothyroidism and this can be explained as follows. Since the thyroid is not able to produce adequate amounts of T4 and T3, the pituitary senses this and increases TSH (Thyroid stimulating hormone) production which stimulates the thyroid to increase T4and T3 production.

In case of secondary hypothyroidism, the pituitary gland itself fails to produce enough TSH and hence the levels of TSH as well asT4 and T3 will be below normal in the blood.

Some important points to remember are:

• Symptoms may not always correspond to the severity of the lab test abnormalities i.e. some patients may have severe hypothyroidism as revealed by their laboratory values but they may have very mild symptoms.
• On the other hand, some patients may not have significantly abnormal values but they may be having significant symptoms.
• It is important to remember that the treatment must not only correct the laboratory values but also make the patient feel better.
• During the initial stages of Hypothyroidism, increased conversion of T4 to T3 occurs and hence T3 levels are maintained but T4 levels may be low to normal.

In order to diagnose Hashimoto’s Thyroiditis (as an etiology of primary thyroid failure), Anti-TPO antibody testing may be done. The Anti-TPO Ab which was previously referred to as the Antimicrosomal antibody (AMA) is a useful marker for the diagnosis and management of autoimmune thyroid disease.

Ultrasonography (USG) of the neck and thyroid can be used to detect nodules and infiltrative disease.