CFS; Fatigue - chronic; Immune dysfunction syndrome

The exact cause of chronic fatigue syndrome (CFS) is unknown. Some researchers suspect it may be caused by a virus, such as Epstein-Barr virus or human herpes virus-6 (HHV-6). However, no specific virus has been identified as the cause.

Studies suggest that CFS may be caused by inflammation along the nervous system, and that this inflammation may be some sort of immune response or process.

Other factors such as age, prior illness, stress, environment, or genetics may also play a role.

CFS most commonly occurs in women ages 30 to 50.

The Centers for Disease Control (CDC) describes CFS as a distinct disorder with specific symptoms and physical signs, based on ruling out other possible causes. The number of persons with CFS is unknown.

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