Symptoms:

Symptoms of CFS are similar to those of most common viral infections (muscle aches, headache, and fatigue). They come on within a few hours or days and last for 6 months or more.

Main symptoms:

• Fatigue or tiredness, never experienced to this extent before (new onset), lasting at least 6 months and not relieved by bed rest
• Fatigue that is severe enough to restrict activity (serious fatigue develops with less than one-half of the exertion compared with before the illness)

Other symptoms:

• Fatigue lasting more than 24 hours after an amount of exercise that would normally be easily tolerated
• Feeling unrefreshed after sleeping an adequate amount of time
• Forgetfulness or other similar symptoms including difficulty concentrating, confusion, or irritability
• Headaches, different from previous headaches in quality, severity, or pattern
• Joint pain, often moving from joint to joint (migratory arthralgias), without joint swelling or redness
• Lymph node tenderness in the neck or armpit
• Mild fever (101 degrees F or less)
• Muscle aches (myalgias)
• Muscle weakness, all over or multiple locations, not explained by any known disorder
• Sore throat

Signs and tests:

Physical examination may confirm the fever, lymph node tenderness, lymph node swelling, or other symptoms. The throat may appear red without drainage or pus.

The health care provider will diagnose chronic fatigue syndrome (CFS) only after ruling out all other known possible causes of fatigue, such as:

• Drug dependence
• Immune or autoimmune disorders
• Infections
• Muscle or nerve diseases (such as multiple sclerosis)
• Endocrine diseases (such as hypothyroidism)
• Other illnesses (such as heart, kidney, liver diseases)
• Psychiatric or psychological illnesses, particularly depression (since CFS itself may be associated with depression, a diagnosis of depression does not rule out CFS but fatigue related to depression alone must be ruled out for CFS to be diagnosed)
• Tumors

A diagnosis of CFS must include:

• Absence of other causes of chronic fatigue (excluding depression)
• At least four of the other symptoms listed
• Extreme, prolonged fatigue

There are no specific tests to confirm the diagnosis of CFS, though a variety of tests are usually done to exclude other possible causes of the symptoms.

The following test results, while not specific enough to diagnose CFS, are seen consistently in people who are eventually diagnosed with the disorder:

• Brain MRI showing swelling in the brain or destruction of part of the nerve cells (demyelination)
• Higher levels of specific white blood cells (CD4 T cells) compared with other types of white blood cells (CD8 T cells)
• Specific white blood cells (lymphocytes) containing active forms of EBV or HHV-6