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What is the most severe complication of hypothyroidism?

Hypothyroidism, also known as underactive thyroid disease, is a common condition where the thyroid gland does not produce enough thyroid hormones. Thyroid hormones play an important role in regulating metabolism, heart rate, body temperature, and many other essential body functions. When thyroid hormone levels are low, a variety of symptoms and complications can occur.

While hypothyroidism is generally easily managed with thyroid hormone replacement medication, if left untreated it can lead to a number of health problems. Some of the potential complications of untreated hypothyroidism include:

  • Goiter (enlarged thyroid gland)
  • Joint or muscle pain
  • Depression
  • Impaired memory and concentration
  • Fatigue
  • Constipation
  • Weight gain
  • Infertility
  • Irregular or heavy menstrual periods

For most patients, taking levothyroxine (synthetic thyroid hormone) daily helps manage hypothyroidism and prevent complications. However, there is one particularly severe complication that can occur if hypothyroidism is left untreated for a long period of time – myxedema coma.

What is Myxedema Coma?

Myxedema coma is a life-threatening, extreme form of hypothyroidism. It is a medical emergency that requires immediate intensive care treatment.

Myxedema coma occurs when severe, longstanding hypothyroidism causes extreme bodily changes that result in unconsciousness, hypoventilation (reduced breathing), hypothermia (low body temperature), and a variety of metabolic abnormalities.

Some of the symptoms and characteristics of myxedema coma include:

  • Low respiration rate
  • Low blood pressure
  • Hypothermia – body temperature below 95°F (35°C)
  • Unconsciousness or coma
  • Hypoventilation
  • Enlarged tongue
  • Puffy face
  • Delayed reflexes

Myxedema coma has a high mortality rate if untreated, estimated between 30-60%. Death usually occurs due to respiratory depression, infection, or cardiovascular collapse.


Myxedema coma usually occurs in someone with a history of hypothyroidism that has gone undetected or untreated for an extended period of time. Typical causes include:

  • Longstanding, undiagnosed hypothyroidism
  • A hypothyroid patient stops taking their thyroid hormone medication
  • A hypothyroid patient is experiencing medication malabsorption
  • Hypothyroid patient develops an additional illness that stresses the body

Because it takes a significant amount of time for thyroid hormone depletion to build up, myxedema coma is rare. It is most likely to occur in older persons over age 60 with untreated hypothyroidism.

Certain triggers or stressors that can precipitate the onset of myxedema coma include:

  • Infection – pneumonia, urinary tract infection, sepsis
  • Stroke
  • Exposure to cold temperatures
  • Trauma
  • Medications that depress respiration, like sedatives


Diagnosing myxedema coma begins with a physical examination and medical history. Some of the key signs that may lead to a diagnosis of myxedema coma include:

  • Decreased body temperature – below 95°F (35°C)
  • Bradycardia (slow heart rate)
  • Hypotension (low blood pressure)
  • Delayed reflexes
  • Puffy face, hands, and feet
  • Low breathing rate
  • Lethargy, confusion, unconsciousness

Laboratory testing can help confirm the diagnosis. These may include:

  • Thyroid function tests showing very low T3 and T4 levels
  • Elevated TSH levels
  • Low levels of sodium and other electrolytes
  • Elevated creatine kinase
  • CBC may show anemia and low white blood cell count
  • Blood gas analysis may show respiratory acidosis
  • Cultures to check for underlying infection

Imaging like CT or MRI scans of the brain may also be done to rule out stroke or hemorrhage.


Myxedema coma constitutes a medical emergency requiring hospitalization, typically in an intensive care unit. The main goals of treatment are to stabilize the patient, restore normal metabolic function, and treat the underlying thyroid hormone deficiency.

Treatment generally involves:

  • Thyroid hormone replacement – Intravenous synthetic T3 and sometimes T4 are given to reverse the hormonal deficits. Oral doses may be given later to maintain levels.
  • Respiratory support – Mechanical ventilation may be required if respiratory depression is severe.
  • Corticosteroids – Given to help improve neurological and cardiovascular function.
  • Treatment of hypothermia – Warming blankets and fluids are used to bring body temperature back to normal.
  • Treatment of underlying infection – Antibiotics administered if sepsis or other infection caused myxedema coma.
  • Treating other complications – Low blood pressure, electrolyte abnormalities, seizures, etc. are managed as they arise.

With aggressive treatment, reversal of the coma state can begin in 24-48 hours. Mechanical ventilation is typically required for one to two weeks. The hospital stay may last several weeks, as long-term thyroid hormone replacement and monitoring is needed to prevent a relapse.


The key to preventing severe complications like myxedema coma is early detection and proper treatment of hypothyroidism. Some tips for prevention include:

  • Routine screening for thyroid dysfunction, especially in women over age 50.
  • Taking thyroid medication regularly as prescribed.
  • Not stopping thyroid medication unless instructed by a doctor.
  • Prompt medical attention for symptoms like fatigue, weight gain, feeling cold, dry skin.
  • Seeking timely treatment for illnesses, injuries to prevent stresses on the body.
  • Carrying medical ID about hypothyroidism.
  • Patient education on the importance of medication compliance.

Risk Factors

Certain factors can increase the risk of developing myxedema coma if you have untreated hypothyroidism. These include:

  • Older age, especially 60 years or older
  • Living alone or in isolation
  • Having another chronic illness
  • Taking medications that depress respiration
  • Surgical or medical trauma
  • Exposure to cold temperatures
  • Infection that goes untreated
  • Not having regular lab screening of TSH levels


If recognized early and treated aggressively, many patients with myxedema coma can make a full recovery. However, mortality rates remain high even with rapid treatment. Death is most often due to:

  • Severe infection or sepsis
  • Respiratory failure
  • Cardiovascular collapse
  • Cerebrovascular crisis

Studies show that patients diagnosed and treated before loss of consciousness have mortality rates around 20%. For those with myxedema coma involving unconsciousness, mortality rates are 30-60%.

Older patients and those with other chronic illnesses tend to have higher mortality rates. Hypoventilation and low body temperature at time of admission are also associated with poorer outcomes.

With intensive care and continued follow-up after hospital discharge, many patients can regain normal thyroid function and avoid recurrence of myxedema coma.


Myxedema coma represents an end-stage, life-threatening form of untreated hypothyroidism. For patients with longstanding hypothyroidism, it can arise from an infection, illness, or exposure to cold. Quick medical attention and thyroid hormone therapy are needed to reverse the process and stabilize the patient.

To prevent this catastrophic outcome, early detection and treatment of hypothyroidism is key. Patients also need education on taking thyroid medication regularly and not stopping without medical guidance. While still a significant cause of mortality today, the prognosis for myxedema coma continues to improve with greater recognition and more advanced critical care treatment options.