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What is the highest level of hypothyroidism?

Hypothyroidism occurs when the thyroid gland does not produce enough thyroid hormone. This can cause a variety of symptoms including fatigue, weight gain, feeling cold, dry skin, hair loss, muscle weakness, constipation, depression, and irregular menstrual cycles in women. There are varying levels of hypothyroidism depending on how much thyroid hormone is lacking. The most severe form of hypothyroidism is called myxedema coma and represents the highest level of hypothyroidism.

Levels of Hypothyroidism

There are several levels of hypothyroidism that can occur:

Subclinical Hypothyroidism

This is a mild form of hypothyroidism where thyroid hormone levels are slightly elevated but not high enough to cause symptoms. People may have no outward symptoms but can have mild hormonal imbalances. Treatment is often not needed if levels remain stable.

Mild Hypothyroidism

In mild hypothyroidism, thyroid hormone levels are more significantly decreased. Symptoms are typically mild and may include fatigue, weight gain, feeling cold, and muscle aches. Mild hypothyroidism usually responds well to thyroid hormone replacement medication.

Moderate Hypothyroidism

With moderate hypothyroidism, thyroid hormone levels are low enough to cause more troublesome symptoms. People often have fatigue, weight gain, feeling cold, muscle weakness, dry skin, hair loss, constipation, and irregular menstrual cycles. Treatment with thyroid medication is recommended to prevent symptoms from worsening.

Severe Hypothyroidism

In severe hypothyroidism, thyroid hormone levels are very low. Symptoms are typically more intense and people may have severe fatigue, depression, forgetfulness and confusion, swelling around the eyes, slowed movements and speech, and numbness or tingling in the hands. Hospitalization for treatment may be needed.

Myxedema Coma

Myxedema coma represents the highest and most severe level of untreated hypothyroidism. It is a rare, life-threatening form of hypothyroidism that occurs due to long-standing, undiagnosed hypothyroidism. Myxedema coma can result from any cause of hypothyroidism, most commonly Hashimoto’s thyroiditis.

Some key facts about myxedema coma:

  • It represents thyroid hormone levels that are extremely low, typically
  • It is accompanied by severe hypothyroid symptoms along with decreased mental status and hypothermia.
  • The mortality rate with aggressive treatment is 20-50%. Without treatment, myxedema coma is usually fatal.
  • It is often triggered by infection, cold exposure, trauma, medication changes, or other metabolic stress.
  • Treatment involves intravenous thyroid hormone replacement and management of precipitating causes.

Myxedema coma gets its name from some of its characteristic features. “Myxedema” refers to the swelling caused by fluid accumulating in subcutaneous tissues, giving the skin a swollen, puffy appearance. “Coma” indicates that the person has depressed mental function and is unresponsive.


Some of the symptoms and signs that occur in myxedema coma include:

  • Severely decreased mental status – confusion, psychosis, extreme lethargy, possibly coma
  • Hypothermia – body temperature may be below 95 F (35 C)
  • Bradycardia – slow heart rate, often less than 60 bpm
  • Hypotension – low blood pressure
  • Hypoventilation – decreased rate and depth of breathing
  • Anemia
  • Pericardial or pleural effusion – fluid build-up around heart or lungs
  • Decreased gut motility, ileus, or megacolon

In addition to the life-threatening symptoms listed above, myxedema coma patients also demonstrate very severe hypothyroidism symptoms including:

  • Puffy, swollen facial features and extremities
  • Dry, coarse skin
  • Hair loss
  • Slow movements and speech
  • Poor reflexes
  • Low muscle tone and weakness
  • Joint stiffness
  • Difficulty swallowing
  • Macroglossia – enlarged tongue
  • Periorbital puffiness – puffy eyes and eyelids


Myxedema coma usually occurs in someone with a history of hypothyroidism that has been untreated or undertreated. Typical causes include:

  • Hashimoto’s thyroiditis – autoimmune destruction of the thyroid
  • Iodine deficiency – lack of iodine intake
  • Surgical removal of the thyroid
  • Radiation treatment to the thyroid
  • Medications – lithium, interleukin-2, amiodarone
  • Pituitary disease
  • Congenital hypothyroidism

While it usually occurs in those with untreated hypothyroidism, myxedema coma may be triggered by:

  • Infection – pneumonia, urinary tract infection, cellulitis
  • Trauma or surgery
  • Cold exposure
  • Stroke
  • Medication changes – especially sedatives, anesthetics, narcotics, lithium
  • Stopping thyroid medication abruptly
  • Heart attack or other metabolic stress

Risk Factors

Those at increased risk of myxedema coma include:

  • Elderly women – over 60 years old
  • Those with long-standing hypothyroidism
  • Individuals with Hashimoto’s thyroiditis
  • People with suboptimal thyroid treatment
  • Those who have stopped thyroid medication
  • Patients with recent illness, surgery, or trauma
  • Individuals exposed to cold temperatures
  • Those taking sedatives, anesthetics, lithium, amiodarone
  • People with pituitary disorders or adrenal insufficiency


Myxedema coma is primarily a clinical diagnosis based on symptoms, along with extremely low thyroid hormone levels. Diagnostic testing may include:

  • Thyroid function tests – TSH, T3, T4. TSH is markedly elevated, T4 and T3 are very low.
  • Complete blood count – may show anemia, low white blood cell count
  • Basic metabolic panel – may indicate electrolyte imbalances, kidney dysfunction
  • Liver function tests
  • Cortisol levels – adrenal insufficiency may be present
  • Blood glucose
  • Blood cultures to check for infection
  • Chest X-ray if pneumonia is suspected
  • ECG to evaluate heart rate and rhythm
  • CT scan of head if stroke is suspected

Identifying and treating any precipitating illness or event is also important in managing myxedema coma.


Myxedema coma is a medical emergency requiring hospitalization in an intensive care unit. Treatment focuses on:

1. Thyroid Hormone Replacement

Intravenous thyroid hormone is given to correct the severe hormone deficiency. Typical treatments include:

  • T3 initially given as bolus of 10-20 mcg, then 10-25 mcg every 4 hours
  • T4 initially given as bolus of 200-500 mcg, then 50-100 mcg daily
  • Oral replacement may be switched to once mentation improves
  • Daily thyroid function testing to guide dosing

2. Supportive Care

This involves treating symptoms and stabilizing vital functions:

  • Warming blankets and warm environment to treat hypothermia
  • Oxygen, intubation, and mechanical ventilation if needed for hypoventilation
  • IV fluids for dehydration and hypotension
  • Medications like vasopressors for low blood pressure
  • Treating infections with antibiotics if present
  • Nutritional support with IV dextrose and vitamins
  • Cautious use of sedatives due to risk of worsening respiratory depression

3. Treatment of Underlying Causes

Any triggers such as infection, medications, or other illness should be managed.

4. Preventing Recurrence

Once stabilized, patients require ongoing oral thyroid hormone replacement. This is crucial to prevent a relapse of severe hypothyroidism. Patients should be educated about hypothyroidism, the importance of taking their medication regularly, and avoiding triggers. Regular medical follow-up is also important.


Myxedema coma has a high mortality rate even with treatment. Complications can include:

  • Worsening hypothermia
  • Hypoventilation leading to respiratory failure
  • Bradycardia progressing to asystole
  • Hypotension progressing to shock
  • Sepsis from untreated infection
  • Gastrointestinal bleeding or ileus
  • Cerebrovascular events like stroke
  • Cardiac arrest or heart failure
  • Pulmonary embolism
  • Coma and death

Severe hypothyroidism can cause permanent cognitive impairment as well. Those who survive myxedema coma have an increased risk of recurrence if their thyroid condition is not managed appropriately.


With early diagnosis and proper treatment, the prognosis for myxedema coma can be good. However, mortality remains high even with optimal treatment. Death rates are estimated around:

  • 20-50% with appropriate treatment
  • Almost 100% without treatment

Prognosis depends on factors like:

  • How quickly treatment is started
  • The person’s age and health status
  • Presence of precipitating factors like infection
  • How severe hormone depletion and symptoms are
  • Development of complications like heart failure or sepsis

Lower mortality rates around 20% are seen with rapid thyroid hormone replacement and treatment of underlying infection or other triggers. But if treatment is delayed and complications develop, mortality remains high around 50-60%.


The best way to prevent myxedema coma is through proper screening and treatment for hypothyroidism before it gets to this extreme, life-threatening level. Important preventive measures include:

  • Routine TSH screening in adults, especially women over 50
  • Testing for thyroid issues in those with symptoms or high risk
  • Treating hypothyroidism with appropriate thyroid hormone replacement
  • Taking thyroid medication regularly as prescribed
  • Regular follow-up of TSH levels to ensure proper dosing
  • Educating patients about hypothyroidism management
  • Minimizing use of drugs that can suppress thyroid function
  • Avoiding abrupt withdrawal of thyroid medication
  • Managing comorbid illnesses to avoid precipitating triggers
  • Seeking medical attention promptly for signs of worsening hypothyroidism

These strategies help prevent severe thyroid hormone deficiency and allow for early intervention before myxedema coma develops.


Myxedema coma represents the highest severity level of untreated hypothyroidism. It is characterized by extremely low thyroid hormone levels along with hypotension, hypothermia, hypoventilation, and decreased mental status. Myxedema coma is often triggered by events like infection or cold exposure in those with long-standing hypothyroidism.

Though it is rare, myxedema coma has a mortality rate around 20-50% even with optimal treatment. Rapid thyroid hormone replacement and intensive care support are needed. With appropriate therapy and prevention of hypothyroid progression, this life-threatening complication can potentially be avoided. Ongoing patient education and medical monitoring is key for the proper management of hypothyroidism.