CFS has been reported in most industrialized countries and is most prevalent among women between the ages of 20 and 50. Seventy percent of CFS patients have allergies, and seventy percent also have abnormalities in cranial blood flow. Experts doubt that CFS is hereditary, but it does seem to run in some families. Symptoms include an abrupt onset of flu-like complaints, with overwhelming fatigue lasting for at least six months, and the absence of any other medical disorder that explains such symptoms. These two basic criteria must be accompanied by at least eight other criteria, including fever, sore throat, tender lymph nodes, muscle and joint pain, severe headaches, sleep disturbance, and significant memory and reasoning lapses.
Diagnosis is made by ruling out other possible causes of fatigue.
The cause of CFS remains a mystery. A virus or viruses, bacterium, allergens, or environmental toxins may all precipitate CFS, according to some experts. Other evidence suggests that CFS patients have an overactive immune system, which produces immune proteins long after a viral threat is over. Most patients undertake a trial of antidepressant therapy, even if major depression is not present. Avoidance of strenuous exercise and administration of symptom-specific drug therapy is often prescribed.