The best definition of FMS and explanation of symptoms that I have found come from Dr. Devin Starlanyl's site:

"FMS is not new. It was first described by William Balfour, a surgeon at the University of Edinburgh, in 1816. The medical profession called it many different names, including chronic rheumatism, myalgia, pressure point syndrome, and fibrositis. The condition was also thought to be psychological by some physicians, but that notion must now be relegated to the Dark Ages of medicine.

In 1987, the American Medical Association (AMA), recognized FMS as a true illness and a major cause of disability. Now, nearly ten years later, it is still, unfortunately, too often dismissed as the "newest fad disease", and most physicians still lack the knowledge to diagnose and treat it.

FMS is not a catchall, "wastebasket" diagnosis. FMS is a specific, chronic non-degenerative, non-progressive, non-inflammatory, truly systemic pain condition.

Diseases have known causes and well-understood mechanisms for producing symptoms. FMS is called a syndrome, which means it is a specific set of signs and symptoms that occur together. Don't let this fool you into thinking that fibromyalgia is any less serious or potentially disabling than a disease. Rheumatoid arthritis, lupus, and other serious afflictions are also classified as syndromes. Lab tests for fibromyalgia are valid only to rule out other conditions. There is no blood test that can accurately identify fibromyalgia.

The official definition requires that tender points must be present in all four quadrants of the body -- that is, the upper right and left and lower right and left parts of your body. You must have had wide-spread, more-or-less continuous pain for at least three months. Tender points occur in pairs on various parts of the body. Because they occur in pairs, the pain is usually distributed equally on both sides of the body.

In traumatic FMS, tender points are often clustered around an injury instead of, or in addition to, the 18 "official" points required for a patient to be able to enter a clinical fibromyalgia study. These clusters can also occur around a repetitive strain or a degenerative and/or inflammatory problem, such as arthritis.

FMS can occur at any age. Most patients, when questioned carefully, reveal that their symptoms began at an early age. About 25 percent of the FMS patients I see are men. This ratio differs from most sources in the literature. I think that this is due to FMS being underdiagnosed in males.

Flu-like achiness is frequently the most prominent symptom of FMS, but there are many others. For example,

Your eyes may be too dry, but at other times they will water;

Your thermal regulatory system is out of whack. You may notice this thermal fluctuation when you get out of bed (which may be often, due to bladder irritability) during the night;

You may have to wait for your temperature to cool down after getting back in bed before you can pull the bedcover up.

Another symptom of FMS is spasticity (tightness) which can constrict the peripheral blood vessels -- those close to the skin. This symptom, especially in the winter, makes certain parts of our bodies -- most often the buttocks and thighs -- feel like cold slabs of meat. You may experience skin mottling. Fingernails can break off, often in crescent-shaped pieces. If nails do grow, they sometimes start to curve under.

FMS is a sensitivity-amplification syndrome. This means that people with Fibromyalgia can be sensitive to smells, sounds, lights, odors, pressure and temperature fluctuations and vibrations. The noise emitted by fluorescent lights can drive you crazy. FMS sensitizes nerve endings as well as the rest of the autonomic nervous system, which means that the ends of the nerve receptors may have changed shape.

Because of this, for example, your body might interpret touch, light, or sound as pain. Your brain knows pain is a danger signal -- an indication that something is wrong and needs attention -- so it mobilizes its defenses. Then, when those defenses aren't used, you become anxious.

Sleep plays a crucial role in FMS. Perhaps you aren't getting enough sleep, or the right kind of sleep. You may have insomnia, or a host of other sleep-related problems.

People with FMS often have the alpha-delta sleep anomaly. As soon as we reach deep delta level sleep, alpha waves (awake) intrude and either jolt us to an awakening or to a lighter stage of sleep. The body heals and many neurotransmitters are restored during delta sleep, so we soon suffer from sleep deprivation.

Neurotransmitters are electro-biochemical agents that cross nerve synapses. They are the vehicles that carry information back and forth between your body and mind. One might say that neurotransmitters are the "information superhighway" between the body and mind.

Much of our mental and physical sense of continuity and security depends upon our ability to repeat appropriate and predictable actions, but this is disrupted in FMS. Neurotransmitters normally inform muscles constantly about what they're doing so their actions can be modified.

Much of our muscle tension function is improperly controlled by these neurotransmitters. Healthy people think nothing of picking up a glass of water and bringing it to their lips. They know just how tightly their hand has to grip, how heavy the glass of water feels, and how much speed is appropriate to accomplish this act smoothly.

People with Fibromyalgia, however, lack proper sensory feedback. The thumb grasps with too little pressure, and the wrist muscle lets go when flexed. The economy of effort is not there. To enable us to sit, walk, and stand, the entire musculature must be able to feel its own activity, and we often can't do that.

Only about 20% of FMS cases have a known triggering event that initiates the first obvious "flare." During a flare, current symptoms become more intense, and new symptoms frequently develop."

Excerpted from "Fibromyalgia and Chronic Myofascial Pain Syndrome: A Survival Manual" by Devin J. Starlanyl and Mary Ellen Copeland M.A. M.S., © copyright 1996 Devin Starlanyl, All Rights reserved. Please get the book for further information.