Chronic fatigue syndrome (CFS) is a complicated disorder characterized by extreme fatigue that lasts for at least six months and that can't be fully explained by an underlying medical condition. The fatigue worsens with physical or mental activity, but doesn't improve with rest.

Other characteristic symptoms include:

• Sleep that isn't refreshing
• Difficulties with memory, focus and concentration
• Dizziness that worsens with moving from lying down or sitting to standing

This condition is also known as myalgic encephalomyelitis (ME). Sometimes it's abbreviated as ME/CFS. The most recent term proposed is systemic exertional intolerance disease (SEID).

The cause of chronic fatigue syndrome is unknown, although there are many theories — ranging from viral infections to psychological stress. Some experts believe chronic fatigue syndrome might be triggered by a combination of factors.

There's no single test to confirm a diagnosis of chronic fatigue syndrome. You may need a variety of medical tests to rule out other health problems that have similar symptoms. Treatment for chronic fatigue syndrome focuses on improving symptoms.

Symptoms of chronic fatigue syndrome can vary from person to person, and the severity of symptoms can fluctuate from day to day. Signs and symptoms may include:

• Fatigue
• Problems with memory or concentration
• Sore throat
• Headaches
• Enlarged lymph nodes in your neck or armpits
• Unexplained muscle or joint pain
• Dizziness that worsens with moving from lying down or sitting to standing
• Unrefreshing sleep
• Extreme exhaustion after physical or mental exercise

When to see a doctor

Fatigue can be a symptom of many illnesses, such as infections or psychological disorders. In general, see your doctor if you have persistent or excessive fatigue.

The cause of chronic fatigue syndrome is still unknown. Some people may be born with a predisposition for the disorder, which is then triggered by a combination of factors. Potential triggers include:

• Viral infections. Because some people develop chronic fatigue syndrome after having a viral infection, researchers question whether some viruses might trigger the disorder. Suspicious viruses include the Epstein-Barr virus, human herpes virus 6. No conclusive link has yet been found.
• Immune system problems. The immune systems of people who have chronic fatigue syndrome appear to be impaired slightly, but it's unclear if this impairment is enough to actually cause the disorder.
• Hormonal imbalances. People who have chronic fatigue syndrome also sometimes experience abnormal blood levels of hormones produced in the hypothalamus, pituitary glands or adrenal glands. But the significance of these abnormalities is still unknown.
• Physical or emotional trauma. Some people report that they experienced an injury, surgery or significant emotional stress shortly before their symptoms began.

Factors that may increase your risk of chronic fatigue syndrome include:

• Age. Chronic fatigue syndrome can occur at any age, but it most commonly affects young to middle-aged adults.
• Sex. Women are diagnosed with chronic fatigue syndrome much more often than men, but it may be that women are simply more likely to report their symptoms to a doctor.

Possible complications of chronic fatigue syndrome include:

• Lifestyle restrictions
• Increased work absences
• Social isolation
• Depression

There's no single test to confirm a diagnosis of chronic fatigue syndrome. Symptoms can mimic those of many other health problems, including:

• Sleep disorders. Chronic fatigue can be caused by sleep disorders. A sleep study can determine if your rest is being disturbed by disorders such as obstructive sleep apnea, restless legs syndrome or insomnia.
• Medical problems. Fatigue is a common symptom in several medical conditions, such as anemia, diabetes and underactive thyroid (hypothyroidism). Lab tests can check your blood for evidence of some of the top suspects.
• Mental health issues. Fatigue is also a symptom of a variety of mental health problems, such as depression and anxiety. A counselor can help determine if one of these problems is causing your fatigue.

It's also common for people who have chronic fatigue syndrome to also have other health problems at the same time, such as sleep disorders, irritable bowel syndrome, fibromyalgia, depression or anxiety.

In fact, there are so many overlapping symptoms between chronic fatigue syndrome and fibromyalgia that some researchers consider the two disorders to be different aspects of the same disease.

Diagnostic criteria

Guidelines proposed by the United States Institute of Medicine define the fatigue associated with chronic fatigue syndrome as being:

• So severe that it interferes with the ability to engage in pre-illness activities
• Of new or definite onset (not lifelong)
• Not substantially alleviated by rest
• Worsened by physical, mental or emotional exertion

To meet the Institute of Medicine's diagnostic criteria for chronic fatigue syndrome, a person would also need to experience at least one of these two symptoms:

• Difficulties with memory, focus and concentration
• Dizziness that worsens with moving from lying down or sitting to standing

These symptoms must last for at least six months and occur at least half the time at moderate, substantial or severe intensity.

There is no cure for chronic fatigue syndrome. Treatment focuses on symptom relief. The most disruptive or disabling symptoms should be addressed first.

Medications

Some problems associated with chronic fatigue syndrome can be improved with either prescription or over-the-counter medications. Examples include:

• Depression. Many people with long-term health problems, such as chronic fatigue syndrome, are also depressed. Treating your depression can make it easier for you to cope with the problems associated with chronic fatigue syndrome. Low doses of some antidepressants can also help improve sleep and relieve pain.
• Orthostatic intolerance. Some people with chronic fatigue syndrome, particularly adolescents, feel faint or nauseated when they stand or sit upright. Medications to regulate blood pressure or heart rhythms may be helpful.
• Pain. If over-the-counter medications such as ibuprofen (Advil, Motrin IB, others) and naproxen sodium (Aleve) don't help enough, prescription drugs sometimes used to treat fibromyalgia might be options for you. These include pregabalin (Lyrica), duloxetine (Cymbalta), amitriptyline or gabapentin (Neurontin).

Therapy

Many people with chronic fatigue syndrome benefit from:

• Counseling. Talking with a counselor can help build coping skills to deal with chronic illness, address limitations at work or school, and improve family dynamics. It can also be helpful for managing depression.
• Addressing sleep problems. Sleep deprivation can make other symptoms more difficult to deal with. Your doctor might suggest avoiding caffeine or changing your bedtime routine. Sleep apnea can be treated by using a machine that delivers air pressure through a mask while you sleep.
• Exercise. Aggressive exercise regimens often lead to worsened symptoms, but maintaining activities that are tolerated is important to prevent deconditioning. Exercise regimens that start at a very low intensity and increase very gradually over time may be helpful in improving long-term function.

Post-exertional malaise

People with chronic fatigue syndrome have a worsening of their symptoms after physical, mental or emotional effort. This is called post-exertional malaise and it can last for days or weeks after the exertion.

People who experience post-exertional malaise often struggle to find a good balance between activity and rest. The goal is to remain active without overdoing it.

You may want to keep a daily diary of your activities and symptoms, so you can track how much activity is too much for you. This may help you avoid pushing too hard on the days you feel good, which can result in a "crash" where you feel much worse later.

Many alternative therapies have been promoted for chronic fatigue syndrome, but there's not much evidence that they work. Patients with chronic fatigue syndrome may be sensitive to medications, including herbal products and supplements. Treatments that are expensive or potentially harmful should be avoided.

The experience of chronic fatigue syndrome varies from person to person. Emotional support and counseling may help you and your loved ones deal with the uncertainties and restrictions of this disorder.

You may find it therapeutic to join a support group and meet other people with chronic fatigue syndrome. Support groups aren't for everyone, and you may find that a support group adds to your stress rather than relieves it. Experiment and use your own judgment to determine what's best for you.

If you have signs and symptoms of chronic fatigue syndrome, you're likely to start by seeing your family doctor or a general practitioner. It can be difficult to absorb all of the information provided during an appointment, so you might want to arrange for a friend or family member to accompany you. Having someone else hear the information can help you later in case there's something you missed or forgot.

What you can do

Before your appointment, you may want to write a list that includes:

• Your signs and symptoms. Be thorough. While fatigue may be affecting you most, other symptoms — such as memory problems or headaches — also are important to share with your doctor.
• Key personal information. Recent changes or major stressors in your life can play a very real role in your physical well-being.
• Health information. List any other conditions for which you're being treated and the names of any medications, vitamins or supplements that you take regularly.
• Questions to ask your doctor. Creating your list of questions in advance can help you make the most of your time with your doctor.

For chronic fatigue syndrome, some basic questions to ask your doctor include:

• What are the possible causes of my symptoms or condition?
• What tests do you recommend?
• If these tests don't pinpoint the cause of my symptoms, what additional tests might I need?
• On what basis would you make a diagnosis of chronic fatigue syndrome?
• Are there any treatments or lifestyle changes that could help my symptoms now?
• Do you have any printed materials I can take with me? What websites do you recommend?
• What activity level should I aim for while we're seeking a diagnosis?
• Do you recommend that I also see a mental health provider?

Don't hesitate to ask other questions during your appointment as they occur to you.

What to expect from your doctor

Your doctor is likely to ask you a number of questions, such as:

• What are your symptoms and when did they begin?
• Does anything make your symptoms better or worse?
• Do you have problems with memory or concentration?
• Are you having trouble sleeping?
• How often do you feel depressed or anxious?
• How much do your symptoms limit your ability to function? For example, have you ever had to miss school or work because of your symptoms?
• What treatments have you tried so far for this condition? How have they worked?