|
|
[Ed. Note: The following is
reprinted from the National Institutes of Health website,
www.nih.gov ]
May 19, 2006 --
A new study shows that a reduction in small-diameter nerve fibers is evident
in the devastating chronic pain syndrome known as complex regional pain
syndrome-type I (CRPS-I), which was formerly known as reflex sympathetic
dystrophy. This finding of nerve damage could provide a biomarker, or
aspecific physical trait, that clinicians could use in the future to help
diagnose and measure the natural history ofCRPS.
The study of human skin biopsies provides some of the first evidence of a
physical abnormality underlying CRPS-I. The results are published in the
February issue of the journal Pain* and were funded in part by the
National Institute of Neurological Disorders and Stroke (NINDS).
CRPS develops when a portion of the nervous system that normally conducts
pain signals becomes electrically overactive. This phenomenon results in
spontaneous pain. In the past, many doctors believed that this mysterious
pain syndrome was a psychosomatic illness. CRPS type II, once known as
causalgia, refers to pain after a nerve injury. CRPS-type I, formerly known
as reflex sympathetic dystrophy (RSD), occurs in patients most often after
trauma, but without clear nerve injury. Pain and other symptoms persist
long after the initial injury has healed. The chronic pain of CRPS-I may
emerge following a cut, burn, fracture, sprain, infection, surgery, or
arthritis. Coronary artery disease and stroke may also be associated with
onset of the disorder. Unlike conditions such as stroke, CRPS has no known
risk factors and can affect anyone. The patient's arms or legs are usually
involved, but CRPS may affect any part of the body. Patients also have
other changes in the pain site such as swelling or changes in skin color
“CRPS is not really a disease process but a symptom complex. It has been
difficult to accurately identify CRPS patients,” says lead author Anne
Louise Oaklander, MD, PhD, from Massachusetts General Hospital and Harvard
Medical School in Boston. “However, absence of proof is not the proof of
absence. With CRPS a great cross-section of people can be affected, since
even drawing blood can bring it on. The person can look absolutely fine on
the outside but still can suffer from devastating pain,” says Dr. Oaklander.
Currently, cases of CRPS are hard to prove or disprove. "It is difficult to
see a patient who appears to be in distress, particularly if it's severe,
and who's pleading with you to help, when you don't quite know what to do,
," Dr. Oaklander says. “Patients want an objective cause for their symptoms
to be identified.”
The typical neurology tests used to diagnose nerve injuries involve
electromyography (EMG) and nerve conduction techniques that measure major
motor or sensory nerve changes. Unfortunately the fiber nerve injuries in
CRPS are not detected by this standard exam, which only measures large-fiber
function. The difficulty in measuring small-fiber damage led Dr. Oaklander
and her colleagues to propose skin biopsy for detection of CRPS. Skin
biopsy, a procedure in which a sample of skin tissue is removed and
examined, provides a very sensitive method for detecting small nerve fiber
damage. “Skin biopsies are a window into the peripheral nervous system,”
says Dr. Oaklander.
In the study, small skin samples were taken from 18 adults with CRPS-I and
seven people who had chronic pain from osteoarthritis, but not CRPS. Each
subject identified the location of his or her maximum pain, a nearby
symptom-free area on the same limb, and a pain free area on the opposite
limb. Skin biopsies were taken from all three spots and the density of tiny
projections extending from each nerve cell – small nerve fibers, or neurites
– was measured. The results showed a decrease in the number of neurites in
the CRPS-affected regions only. On average, about 30 percent of the neurites
were missing in the affected limbs. The loss of neurites may cause the pain
of CRPS by triggering a hyper-response on the part of the remaining neurons.
The next step for the researchers will be to create and test animal models
that replicate the unique features of CRPS. This animal model may identify
other biomarkers for the presence of the pain in CRPS patients and could
improve medical care for patients with CRPS by providing the first and most
important step of identification. In the meantime, the evidence now
suggests that CRPS is a classifiable neurologic disorder. It also guides
CRPS patients to seek treatments appropriate for nerve injury.
The NINDS is a component of the National Institutes of Health (NIH) in
Bethesda, Maryland, and is the nation’s primary supporter of biomedical
research on the brain and nervous system. The NIH is comprised of 27
Institutes and Centers and is a component of the U. S. Department of Health
and Human Services. It is the primary Federal agency for conducting and
supporting basic, clinical, and translational medical research, and
investigates the causes, treatments, and cures for both common and rare
diseases. For more information about NIH and its programs, visit
http://www.nih.gov/.
*Oaklander AL, Rissmiller JG, Gelman LB, Zheng L, Chang Y, Gott R.
“Evidence of focal small-fiber axonal degeneration in complex regional pain
syndrome-I (reflex sympathetic dystrophy).” Pain, February 2006,
Vol. 120, pp. 235-243.
-By Michelle D. Jones-London, Ph.D.
Return To Table Of Contents
|