Chronic fatigue immune dysfunction syndrome (CFIDS) is a mysterious illness marked by unrelenting exhaustion, muscle pain, cognitive disorders that patients call "brain fog" and a myriad of other physical symptoms. Orthostatic intolerance (OI) is the umbrella term for a number of different nervous system-related disorders that can cause similar symptoms. These two conditions have been associated with one another.

The connection between OI and CFIDS was first explored in 1995 by researchers at Johns Hopkins University, who identified NMH in 96 percent of CFIDS patients. Since then, scientists have learned much more about the broader problem of OI in CFIDS.

DEFINITIONS

CFIDS 
CFIDS also known as chronic fatigue syndrome (CFS), is characterized by fatigue that is medically unexplained, of at least six months' duration, not the result of ongoing exertion, not substantially relieved by rest, and causes a substantial reduction in previous levels of occupational, educational, social or personal activities.

This disabling fatigue must be accompanied by four or more of the following symptoms: impaired memory or concentration; sore throat; tender neck or armpit lymph nodes; muscle pain; headaches of a new type, pattern or severity; unrefreshing sleep; post-exertional malaise lasting more than 24 hours; and multi-joint pain without swelling or redness.

OI
Orthostatic intolerance (OI) is the umbrella term for a family of disorders that cause symptoms when a person stands or sits for a prolonged time. Symptoms of orthostatic intolerance include lightheadedness, dizziness, nausea, fatigue, tremors, breathing or swallowing difficulties, headache, visual disturbances, sweating, and pallor. The two forms of OI that have been linked with CFIDS in research studies are:

• Neurally mediated hypotension (NMH), which involves a precipitous drop in systolic blood pressure (at least 20-25 mm Hg) while standing, plus an increase in symptoms while standing.
• Postural orthostatic tachycardia syndrome (POTS), which causes a rapid increase in heart rate (pulse) of more than 30 beats per minute (bpm) from baseline, or to more than 120 bpm total during the first 10 minutes of standing.

THE POTENTIAL CONNECTION

• The causes of CFIDS and OI are not well understood. Both can start with sudden onset of a flu-like illness.
• It is now thought that the majority of CFIDS patients have some form of OI as a co-existing condition.
• A gene for at least one type of OI has been discovered, and it is not uncommon to find several individuals with CFIDS and OI in the same family.
• OI seems to be a particular problem in children and adolescents with CFIDS. 
• Treatment for OI may resolve at least some symptoms for individuals with CFIDS.

TESTING

CFIDS

• CFIDS is currently a diagnosis by exclusion.
• Patients are usually diagnosed after they meet the Centers for Disease Control and Prevention's case definition/diagnostic criteria and a physical exam and laboratory tests have been done to rule out other possible reasons for symptoms.

OI

• CFIDS patients with NMH or POTS may not develop heart rate or blood pressure changes for several minutes after standing. Therefore, brief, routine tests of heart rate and blood pressure in the usual office visit can miss NMH and POTS.
• Patients with suspected OI typically undergo a head-up tilt table test (HUT) as an outpatient in a hospital or cardiology office. Patients are strapped to a table that is slowly tilted upright and their blood pressure and heart rate monitored for a specified period of time or until OI develops.

TREATMENT

CFIDS

• Treatment of CFIDS is aimed at relief of symptoms such as sleep disorders, pain and gastrointestinal difficulties. No single therapy exists to help all patients.
• Drug therapy, physical therapy and lifestyle changes, including increased rest, reduced stress, dietary restrictions and careful, graduated exercise are often recommended.

OI

• The first line of treatment for OI is non-medical interventions such as increased water and salt consumption (up to 10-15 g sodium daily), tilting the head of the bed up a few degrees, wearing compression garments (such as support hose or girdles) and learning to avoid things that can make OI worse, such as standing in long lines, being in warm environments or eating large, heavy meals.
• Drug therapy may also be used, such as fludrocortisone (Florinef) to treat low blood volume and vasoconstrictor medications, including methylphenidate (Ritalin), dextroamphetamine (Dexedrine) and midodrine (ProAmatine) to treat blood pooling. Sometimes drugs to block the release or effect of epinephrine and norepinephrine are used as well.

ABOUT THE CFIDS ASSOCIATION OF AMERICA

• The CFIDS Association of America is the leading organization dedicated to conquering CFS and related disorders. Since 1987, the Association has invested nearly $12 million in CFIDS education, public policy and research efforts.
• The Association publishes The CFIDS Chronicle, the world's most authoritative and widely read source of information about CFIDS, The CFS Research Review , a source of information on diagnosis, treatment and research for medical professionals.