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What causes coma? 40 possible conditions

What Is a Coma?

A coma is a prolonged state of unconsciousness. A coma occurs when a part of the brain is damaged, either temporarily or permanently. This damage results in unconsciousness, an inability to awake, and unresponsiveness to stimuli such as pain, sound, and light. The word “coma” is derived from the Greek word “koma,” which means “deep sleep” (Koehler & Wijdicks, 2008).

Comas may be caused by an injury, an illness, a stroke, tumors, drugs, alcohol abuse, and other damage to the brain. A person who is in a coma is alive but is unable to move at will, think, speak, or respond to his or her environment. Important functions, such as breathing and blood circulation, remain intact.

A coma is a medical emergency. Doctors need to work quickly to preserve brain life and function, and to keep the patient healthy during the course of his or her coma. A coma may be challenging to diagnose and treat. A coma usually does not last for more than four weeks, and recovery occurs gradually. However, some patients have remained in comas for years or even decades.

What Causes a Coma?

Comas are caused by damage to the brain—specifically, either the diffused bilateral cerebral hemisphere cortex or the reticular activating system, which controls arousal and awareness (Adukauskiene et al, 2008). Comas can be caused by many factors, including head injuries, loss of oxygen, bleeding or pressure in the brain, infections, metabolic problems, and toxic factors. Some examples include:

  • traumatic brain injuries, such as those caused by traffic accidents or violent fights
  • stroke (reduced blood supply to the brain)
  • tumors in the brain or brainstem
  • lack of oxygen to the brain, such as when the patient is rescued from drowning or from a heart attack
  • diabetes, when blood sugar levels become too high (hyperglycemia) or too low (hypoglycemia), which can lead to swelling in the brain
  • overdosing on drugs or alcohol
  • carbon monoxide poisoning
  • buildup of toxins in the body, such as ammonia, urea, or carbon dioxide
  • lead poisoning
  • infections such as meningitis or encephalitis
  • repeated seizures
  • electrolyte imbalance

What Are the Symptoms of a Coma

A coma is a medical emergency and requires immediate medical attention. Signs of a coma include:

  • closed eyes
  • unresponsiveness
  • irregular breathing
  • no response of limbs, except for reflexes
  • no response to pain, except for reflexes
  • pupils not responding to light

How Is a Coma Diagnosed?

People in a coma cannot speak or express themselves in other ways. Doctors must rely on information from loved ones or witnesses, and on any physical signs that may give information about what caused the coma.

A doctor will ask friends and family about any events or symptoms that led up to the coma, details about recent changes in the patient’s life, medical history, and drug-use, including prescription drugs and over-the-counter drugs, as well as recreational drugs.

A doctor will then conduct a physical exam. This might include:

  •    checking reflexes
  •    observing breathing patterns
  •    checking for signs of bruises on the skin that may have been caused by trauma
  •    determining the patient’s response to painful stimuli
  •    observing pupil size

Blood tests and other laboratory tests will be used to test for the following:

  •    blood count
  •    thyroid and liver function
  •    electrolyte levels
  •    carbon monoxide poisoning
  •    drug overdose
  •    alcohol overdose
  •    infections of the nervous system

Doctors may order tests that create images of the brain (brain scans), to locate areas of brain injury and look for signs of brain hemorrhage, tumors, strokes and seizures. These tests include:

  • computerized tomography (CT) scans, which use X-rays to create a detailed image of the brain
  • magnetic resonance imaging (MRI), which uses radio waves and magnets to view the brain; and
  • electroencephalography (EEG), which measures electrical activity inside the brain

How Is a Coma Treated?

Doctors will work first to preserve brain life and function. Antibiotics may be given right away, in case there is an infection in the brain. If the cause of the coma is known, such as in the case of a drug overdose, doctors will administer proper medications to treat the underlying condition. Surgery may be required to reduce swelling in the brain.

Once the patient stabilizes, a team of medical professionals will work with the comatose patient to prevent infections, bedsores, and contractures of the muscles. The team will also make sure to provide the patient with balanced nutrition during his or her coma.

What Can Be Expected Long-Term?

A coma usually does not last for more than four weeks. However, some people may remain in a coma for years. Long-term outcomes depend on what caused the coma and the site of damage to the brain. Prognosis is good for people whose comas are caused by a drug overdose. If the patient has suffered severe brain damage, he or she may never come out of the coma.

Some people emerge from a coma with physical, intellectual, or psychological problems. Patients who remain in a coma for more than a year are unlikely to come out of that state (Mayo, 2012). For these people, the most common cause of death is infection (NIH, 2013).

Article Sources:

  • Adukauskiene, D., Budryte, B. & Karpec, D. (2008). Coma: etiology, diagnosis, and treatment. Medicina (Kaunas), 44(10): 812-819. PMID: 19001840
  • Coma. (2013). National Institutes of Health. Retrieved August 11, 2013, from http://www.nlm.nih.gov/medlineplus/coma.html
  • Coma. (2012). The Mayo Clinic. Retrieved August 12, 2013, from http://www.mayoclinic.com/health/coma/DS00724
  • Koehler, P.J., Wijdicks, E.F.M. (2008). Historical study of coma: looking back through medical and neurological texts. Brain, 131:877-889, doi:10.1093/brain/awm332
Read More

See a list of possible causes in order from the most common to the least.


Head Injury

This condition is considered a medical emergency. Urgent care may be required.

A head injury could be an injury to the brain, skull, or scalp. It can vary in severity depending on the cause. In some cases face swelling can be a sign of a head injury.

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Cardiogenic Shock

This condition is considered a medical emergency. Urgent care may be required.

Cardiogenic shock is a rare condition in which the heart is so damaged that it is unable to supply sufficient blood to bodily organs. Sweating and cold extremities are potential signs of this condition.

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This condition is considered a medical emergency. Urgent care may be required.

Dehydration occurs when you lose more fluid than you drink. The most common cause of water loss from the body is excessive sweating. Headaches, dizziness, and decreased urination are symptoms.

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Low Blood Sodium (Hyponatremia)

Low blood sodium, or hyponatremia, occurs when water and sodium are out of balance in your body. A quick drop in sodium levels can cause weakness, headache, nausea, and muscle cramps.

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Low Blood Sugar (Hypoglycemia)

This condition is considered a medical emergency. Urgent care may be required.

Also known as hypoglycemia, low blood sugar can be a dangerous condition. Hypoglycemia is rare in people who are not suffering from diabetes, the chronic disease that affects the body's ability to regulate blood sugar...

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Intracerebral Hemorrhage

This condition is considered a medical emergency. Urgent care may be required.

Intracerebral hemorrhage (ICH) is when blood suddenly bursts into brain tissue, causing damage to the brain. Symptoms usually appear suddenly during ICH.

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This condition is considered a medical emergency. Urgent care may be required.

Septicemia is bacterial infection spread through the entire vascular system of the body. If untreated it can result in sepsis, a life-threatening inflammation.

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Brain Hypoxia

Brain hypoxia, also called cerebral hypoxia, is decreased oxygen in the brain. You are at risk for this condition if you are drowning, choking, suffocating, or in cardiac arrest.

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Brain Abscess

A brain abscess forms when fungi, viruses, or bacteria reach your brain through a wound in your head or an infection somewhere else in your body.

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This condition is considered a medical emergency. Urgent care may be required.

Encephalitis is an inflammation of the brain tissue. It's most often caused by viral infections. In some cases, bacterial infections can cause encephalitis.

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This condition is considered a medical emergency. Urgent care may be required.

Eclampsia is a rare but serious condition that causes seizures during pregnancy. You can develop eclampsia even if you don't have a history of seizures.

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Diabetic Ketoacidosis

This condition is considered a medical emergency. Urgent care may be required.

Diabetic ketoacidosis (DKA) is a serious complication that stems from diabetes. If you don't have enough insulin to help your body process sugars (glucose), your body will start burning fat to fuel itself. As a result...

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Carbon Monoxide Poisoning

This condition is considered a medical emergency. Urgent care may be required.

Carbon monoxide poisoning occurs when we inhale too much carbon monoxide. It can lead to tissue damage and possibly death. Signs include a dull headache, nausea, confusion, and blue lips or skin.

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Meningitis is an inflammation of the membrane that covers the brain and spinal cord. It may cause headache and fever in teens and adults, irritability in babies, and trouble breathing in young children.

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Acute Kidney Tubular Necrosis

This condition is considered a medical emergency. Urgent care may be required.

Inside your kidneys are small tube-shaped structures that remove salt, excess fluids, and waste products from the blood. When these tubules are damaged or destroyed, you develop acute tubular necrosis (ATN). The damag...

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Diabetes Insipidus

Diabetes insipidus (DI) is a rare condition that occurs when your kidneys are not able to conserve water. It results in extreme thirst for water and frequent urination. There are several types of DI, and they can ofte...

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Addisonian Crisis (Acute Adrenal Crisis)

This condition is considered a medical emergency. Urgent care may be required.

People with Addison's disease don't make enough cortisol or aldosterone. Addisonian crisis is a potentially life-threatening condition indicated by nausea, abdominal pain, fever, and chills.

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Glomerulonephritis is a serious illness that can be life-threatening and requires immediate treatment. The condition is sometimes called nephritis.

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Chronic Kidney Disease

Chronic kidney disease (CKD) is the progressive and irreversible destruction of the kidneys. The most common causes of CKD are high blood pressure and diabetes.

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Amphetamine Dependence

Amphetamines are a type of stimulant and can be highly addictive. Consistent amphetamine dependence can lead to overdose, brain damage, and even death.

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This feature is for informational purposes only and should not be used to diagnose.
Please consult a healthcare professional if you have health concerns.