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

Physical examination may show:

• Fever
• Lymph node swelling
• Lymph node tenderness
• Redness in the throat without drainage or pus

A diagnosis of CFS must include:

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

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

There have been reports of CFS patients being found positive on the following tests:

• 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