Physiologic Factors Involved in Fibromyalgia, Contradicting...

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Physiologic Factors Involved in Fibromyalgia, Contradicting Psychogenic

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NEW YORK (Reuters Health) Jun 19 - Functional magnetic resonance imaging

(fMRI) and neuroendocrine studies of people with fibromyalgia reinforce the

notion that altered responses to pain and exercise are physiologically

based.

" When patients with fibromyalgia tell us that they're tender, that they're

experiencing pain at a much lower [pressure] level than people without the

condition, they are in fact experiencing that pain, " Dr. J. Clauw, of

the University of Michigan Medical Center in Ann Arbor, told Reuters Health.

Two reports in the May issue of Arthritis and Rheumatism are the " first

neurobiological evidence of the veracity of their pain, " he added, referring

to another study in which responses to exercise were measured in

fibromyalgia patients.

Dr. Clauw and colleagues studied 16 people who had been diagnosed with

fibromyalgia and 16 healthy control subjects. All underwent fMRI while a

piston-controlled device applied precisely calibrated pressure to the base

of their left thumbnail.

Fibromyalgia patients reported pain at about half the level of pressure that

caused the same feelings of pain among the healthy controls (p<0.005).

When all study participants received the same level of mild pressure, which

was painful to the fibromyalgia patients, 12 brain areas were activated in

patients with fibromyalgia, but only two were activated in the control

group. Increased blood flow--a surrogate measure of nerve activity,

according to Dr. Clauw--occurred in the primary and secondary somatosensory

cortex, the insula, the putamen, and cerebellum.

Moreover, pain in the control group activated regions in the thalamus, the

anterior cingulate cortex and other regions involved in motor responses,

which were not activated in the patient group. The investigators attribute

these differences to " tonic inhibition maintained by persistent excitatory

input associated with ongoing and spontaneous pain " in fibromyalgia

patients.

Dr. Clauw said the findings suggest that something is awry with the way the

central nervous system processes painful stimuli in fibromyalgia patients,

resulting in a lowered pain threshold. Future research should be aimed at

identifying the problem and working to develop better treatments, he added.

In the second report, Dr. M. and colleagues of the Oregon

Health Sciences University in Portland showed that 20 female fibromyalgia

patients exhibited reduced growth hormone and cortisol responses to an acute

exercise stressor, compared with 10 healthy female control subjects

(p=0.003).

The growth hormone response was restored in the patients, but not increased

in the control subjects, by administration of the potent cholinergic agent

pyridostigmine bromide 1 hour before exercise.

Dr. and his associates conclude that patients with fibromyalgia have

an increased hypothalamic somatostatin tone. They would like to see if

long-term treatment with pyridostigmine would improve growth hormone

production in fibromyalgia.

Both studies imply that regulatory mechanisms localized to the central

nervous system are altered in fibromyalgia, note Drs. Clauw and J.

Crofford, also of the University of Michigan, in an editorial. " Purely

behavioral or psychological factors are not primarily responsible for the

pain and tenderness seen in fibromyalgia, " they assert.

While behavioral factors likely play a role in symptom expression in many of

these patients, resulting in poor role functioning, the commentators note

that this phenomenon is similar for all rheumatic diseases.

Arthritis Rheum 2002;46:1136-1138,1333-1350.