Fibromyalgia May Be Related to a Defect in Growth Hormone Secretion

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More is known about what fibromyalgia syndrome isn’t than what it is. It’s not arthritis, because the joints don’t hurt the muscles do. It’s not chronic fatigue syndrome, even though that, too, is a condition that causes generalized pain.

There is growing evidence that fibromyalgia is a disturbance in the body’s reaction to stress and pain that involves a complex interplay of abnormal hormone responses. Oregon Health & Science University researchers in Portland recently reported that women with fibromyalgia have a defect in growth hormone secretion and suggest that a drug long used to treat myasthenia gravis may correct it.

In the study, 20 women with fibromyalgia and 10 healthy women walk quickly on a treadmill until they were exhausted. Growth-hormone levels went up in healthy women, but not in those with fibromyalgia. (Growth hormone is normally released from the pituitary gland in pulses throughout the day into the blood stream in response to stress, trauma, fasting, or deep-wave sleep. Whenever growth hormone levels rise a signal called somatostatin is sent back to the pituitary from a center in the brain telling the pituitary to stop releasing anymore growth hormone.) However, when the women were given the stress test again after taking Mestinon, a drug that inhibits the hormone somatostatin, those with fibromyalgia had an increase in the growth hormone similar to that of the healthy women. These women could have abnormal high levels of somatostatin, which inhibits their ability to secrete the needed growth hormone.

“It may be that in the past these women had so much stress or trauma that they overstressed their stress response and their reaction has diminished,” says Robert Bennet, professor of medicine at OHSU, who conducted the study.

Tricyclics, an older class of antidepressants that include Elavil, Tofranil, and Sinequan are the most common form of drug therapy for fibromyalgia. They can relax the muscles, and promote the secretion of growth hormone and endorphins, hormones that help fight pain and boost mood. However, only about one-third of people who take tricyclics for this disorder have a significant response. In addition, these drugs have the unpleasant side-effects of grogginess, dry mouth, weight gain and blurred vision.

Another group of fibromyalgia medications are currently undergoing testing and are still unapproved by the FDA. These relieve pain and elevate mood in the same way as tricyclics, but without the toxic side-effects. Pregabalin reduces the release of specific brain chemicals, such as glutamate and noradrenaline, which may cause pain. Early studies of the drug show it is effective in controlling pain due to nerve damage, such as that suffered by people with shingles or diabetics with hand or foot pain.

Milnacipran, which is not as far along in its development as pregabalin, enhances levels of two key brain chemicals, norepinephrine and serotonin that play a role in pain remission. They, too, lead to growth hormone secretion and release, activating cellular function and repair throughout the body.

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