Your symptoms are vague: a feeling of fatigue; some tingling in arms or legs that comes and goes; aching muscles; perhaps a headache.

Are you sick? Or are you just imagining that something's wrong?

Many women who have reported these symptoms to their doctor have been dismissed as hypochondriacs or suffering from anxiety. But the real diagnosis is much more subtle, at least at first.

Those symptoms may indicate one of a host of autoimmune diseases such as lupus or multiple sclerosis that develop gradually over time, and strike women many times more frequently than men.

There are about 80 forms of autoimmune disease, and about 75 percent of them occur in women, most often in their childbearing years. Most are rare diseases, yet taken together, they affect about 50 million Americans, or 20 percent of the population. A thyroid disease called Hashimoto's thyroiditis occurs in women 50 times more often than in men. Even more commonly known diseases such as lupus occur up to nine times more often in women. Due to the subtlety and non-specific symptoms of many autoimmune conditions, several years may elapse before an accurate diagnosis is made, reports the American Autoimmune Related Diseases Association (AARDA).

What is autoimmune disease?

Our immune system helps protect us against microbic invaders intent on causing us harm. But that well-armed system sometimes turns on itself. Instead of recognizing and destroying viruses, bacteria, and other pathogens, it produces antibodies against healthy cells and tissues.

Doctors divide autoimmune diseases in two categories—those that attack a specific organ and those that target many organs. In an autoimmune disease such as Hashimoto's thyroiditis, the thyroid is attacked and destroyed. Lupus is a non-organ-specific disease. It plays no favorites, and attacks all organs.

No one is sure why these diseases occur, or why they occur at a higher rate in women. Several theories have been proposed.

The female hormone estrogen may play a role. Estrogen stimulates the immune system, and testosterone suppresses it. A woman's immune system is revved up by estrogen as a survival technique. After all, a mother needs to be able to survive to care for her children. But that hypervigilant immune system then may backfire, sending it on a rampage against the woman's own body.

Autoimmune diseases tend to run in families, which indicates that genes play a role in determining who gets these diseases. But the family ties are odd—one person may have rheumatoid arthritis and another may have lupus, and a third may have diabetes. The diseases are not passed down directly, only the family of diseases.

At least six different genes appear to be involved in autoimmune diseases.

Environmental factors also affect autoimmune diseases. For lupus patients, the sun can trigger an episode of lupus. For other diseases, certain medications act as triggers. Viral infections also can trigger these diseases, or make them worse.

Current research is exploring the activity of the immune system, and the progression of various types of autoimmune diseases. The National Institutes of Health is considering establishing an Office of Autoimmune Diseases, to help focus research done at different NIH sites on autoimmune issues.

A difficult diagnosis

Autoimmune diseases are difficult to diagnose because so many symptoms are vague and unrelated. Fatigue, a low-grade fever, vague, or poorly described aches and pains—these could be symptoms of many illnesses.

A thorough medical history and family history can provide the first clues to identify the symptoms.

Nonspecific screening tests are available, but some give too many false positives, which can be traumatic for patients and doctors.

Another factor in diagnosis is time. The symptoms for these diseases can develop slowly and may be intermittent.

Because of the difficulty in diagnosing these diseases, some patients spend years visiting one expert or another before finding the answer. AARDA says that the typical patient may spend $50,000 before being correctly diagnosed.

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