Hypothyroidism

What is Hypothyroidism?

Hypothyroidism is a condition in which the thyroid gland does not produce sufficient amounts of the thyroid hormone. As the thyroid gland plays an important role in the body's normal functioning, a thyroid hormone deficiency can affect the body and its proper functioning.

Alternate name

Underactive thyroid / Low thyroid

Is hypothyroidism a medical emergency?

Hypothyroidism is not a medical emergency.

Types

An underactive thyroid can be classified into the following types:

• Primary hypothyroidism: This occurs when the fault is with the thyroid gland, and it fails to produce enough thyroid hormone despite receiving sufficient stimulation to do so.
• Central hypothyroidism: This occurs when the thyroid gland does not receive enough stimulation to produce the thyroid hormone.
• Secondary hypothyroidism: The pituitary gland does not provide sufficient stimulation via thyroid-stimulating hormone (TSH) to the thyroid gland.
• Tertiary hypothyroidism: There is an inadequate release of the thyrotropin-releasing hormone (TRH) from the hypothalamus to stimulate the pituitary gland and, subsequently, the thyroid gland.
• Congenital hypothyroidism: This occurs in newborn infants when there is a developmental defect of the thyroid gland or an inborn error in the metabolism of the thyroid hormone.

Causes

Hypothyroidism results when the levels of the thyroid hormones in the body are low. The following may cause an underactive thyroid:

• Primary hypothyroidism:
  • Iodine deficiency
  • Autoimmune thyroiditis
  • Subacute granulomatous thyroiditis, subacute lymphocytic thyroiditis
  • Postpartum thyroiditis
  • Acute infectious thyroiditis
  • Previous thyroidectomy
  • Previous radio-iodine treatment
  • Previous external beam radiotherapy to the neck
  • Medications
• Central hypothyroidism:
  • Lesions or tumors affecting the pituitary gland
  • Surgery or radiation to the pituitary gland
  • Vascular disorders of the brain
  • Trauma to the brain
  • Medications
  • Autoimmune diseases
  • Infiltrative diseases: Hemochromatosis, thalassemia
  • Infections: Tuberculosis, mycoses, syphilis
• Congenital hypothyroidism:
  • Thyroid dysgenesis: Thyroid is missing at birth
  • Thyroid dyshormonogenesis: Error in thyroid production and metabolism
  • Maternal antibodies or radio-iodine transfer
  • Maternal iodine deficiency

Risk factors 

There is an increased risk of underactive thyroid with the following:

• Gender: Women are more at risk of developing Underactive Thyroid
• Age: The elderly age group are at a greater risk
• Family History of thyroid disease
• Presence of autoimmune disease
• Previously treated with radio-iodine or anti-thyroid medications
• Received radiotherapy to the neck or the upper part of the chest
• Previous thyroid surgery
• Recent pregnancy or delivery (within 6-8 months)

Signs & symptoms 

The symptoms of an underactive thyroid may include:

• Tiredness and lethargy
• Intolerance to cold
• Inability to remember and concentrate
• Constipation and indigestion
• Weight gain
• Poor appetite
• Difficulty breathing
• Hoarseness of voice
• Heavy bleeding during periods and/or irregular periods
• Decreased hearing
• Blurring of vision
• Abnormal sensations

The following are the signs of an underactive thyroid:

• Dry and rough skin
• Cool hands and feet
• Hair loss
• Slow pulse rate
• Swelling of the limbs
• Myxedema (mucopolysaccharide deposits on the skin)
• Carpal tunnel syndrome
• Delayed relaxation of tendon reflexes

Investigations

The investigations that are done to establish a diagnosis of hypothyroidism include:

• Laboratory tests -
  • Thyroid profile: To measure the levels of TSH, T3, and T4 in the blood
• Imaging tests -
  • Ultrasound of the neck and thyroid
  • Colour flow Doppler scanning of the thyroid
• Fine needle aspiration biopsy - If nodules are found in the thyroid

Diagnosis

The diagnosis of an underactive thyroid is established based on medical history, clinical evaluation, and results of the investigations done. The diagnosis can be established as follows based on the levels of TSH in relation to T4:

• Normal TSH and Normal T4 - Normal thyroid function
• Elevated TSH and Low T4 - Overt hypothyroidism
• Normal/Low TSH and Low T4 - Central hypothyroidism
• Elevated TSH and normal T4 - Subclinical hypothyroidism

Treatment options

The treatment of Hypothyroidism aims to reverse the progression of the condition and return the levels of the TSH and the T4 to normal levels.

Medical management

The medical management of low thyroid includes:

• Synthetic thyroid hormone Levothyroxine: It restores the thyroid hormone levels and reverses the progress and the symptoms of hypothyroidism. In individuals who are young and healthy, the full replacement dose is started, and the TSH and T4 levels are regularly monitored. In the elderly and those with heart disease, small doses are given first and gradually increased to the required dose over a period of time.
• In central hypothyroidism, T4 levels are monitored regularly while levothyroxine is given.
• Hypothyroidism in pregnancy: In pregnant women with overt hypothyroidism,
  • Levothyroxine is given till the TSH levels are in the range for that particular trimester
  • TSH levels are assessed every 4 weeks in the first half of pregnancy
  • TSH levels are assessed again at the beginning of the second half of the pregnancy
• In women already taking Levothyroxine before their pregnancy - 2 additional doses of the current dose must be taken. The extra doses are given on two separate days in the week. This is started at the beginning of pregnancy.
• Subclinical hypothyroidism: Levothyroxine supplementation helps to reduce cholesterol levels and arterial wall stiffness, improves blood pressure, and has beneficial effects on the heart. It also helps to strengthen the iron-deficiency anemia that may be present.
• Myxedema coma: Levothyroxine is given intravenously (IV)

Complications 

The complications of hypothyroidism may include the following:

• Goiter: The overactivity of the thyroid gland to produce thyroid hormone results in an increase in its size, which in turn can affect swallowing and breathing
• Heart problems: Increased risk of heart disease and heart failure
• Mental health issues: Depression, memory loss, and reduced mental acuity
• Peripheral neuropathy
• Myxedema coma: Prolonged uncontrolled Low thyroid can lead to extreme cold intolerance, extreme fatigue, drowsiness, and finally coma
• Infertility in women: As low thyroid hormone levels affect ovulation
• Congenital birth defects: Children born to mothers with untreated Low thyroid are at a greater risk of being born with severe physical and mental birth defects
• Untreated hypothyroidism in infants can cause severe mental retardation

The complications of treatment with levothyroxine may include:

• Tachycardia
• Palpitations
• Atrial fibrillation
• Nervousness
• Tiredness
• Headache
• Increased excitability
• Sleeplessness
• Tremors
• Possible angina
• In individuals with adrenal insufficiency that is present along with Low thyroid, it can lead to an adrenal crisis if it is not treated before starting the treatment for hypothyroidism.
• Aggressive thyroid hormone replacement can cause severe heart problems in individuals already suffering from heart disease.
• Older people have an increased risk of osteoporosis and fractures if the hormone replacement is not properly monitored.
• Individuals with severe psychological illness may see an increase in the intensity of their symptoms, such as mania or psychosis.
• Temporary worsening of vision may occur in some individuals.

Prognosis

The prognosis for hypothyroidism is good when diagnosed early and managed well. Untreated hypothyroidism can lead to severe complications and death.

When to contact the doctor or hospital/how to identify the emergency or complications?

It is advisable to seek medical attention if symptoms and signs of hypothyroidism are noticed.

Indications for hospitalization if required

Hospitalization is usually not required for hypothyroidism but may be needed if complications need to be managed.

Screening methods

• Screening is recommended, especially in women over 35 years, once every 5 years. More frequent screening is required for high-risk categories such as:
  • Pregnant women
  • Women over the age of 60 years
  • Individuals with type 1 diabetes or other autoimmune diseases
  • Individuals with a history of radiation to the neck or upper part of the chest
• All children with a family history of central hypothyroidism or symptoms of hypothalamic-pituitary abnormalities or lesions, such as failure to thrive, developmental delay, growth hormone (GH) insufficiency, and delayed or precocious puberty, should be screened for central hypothyroidism
• Screening for central hypothyroidism should be done in all patients with a personal or family history of hypothalamic-pituitary lesions or diseases, moderate to severe head trauma, stroke, prior cranial irradiation, hemochromatosis, or iron overload, as well as when hypothyroid manifestations are present

Suggested clinical specialists/departments to consult for this condition

Specialists from the Department of Endocrinology will attend to hypothyroidism.