FEBRUARY 20, 2020
Emerging research may help doctors devise
better ways to prevent some of the tens of thousands of amputations unrelated
to traumatic injury that occur in the U.S. each year.
Diabetes is the leading cause of nontraumatic
lower limb amputations, including of the toe and foot. That's partly because
diabetes increases risk of peripheral artery disease, or PAD, a narrowing of
major blood vessels in the legs and other areas distant from the heart.
But research emphasizes another problem in the
mix—microvascular disease, impairment of the tiniest blood vessels, which
deliver oxygen and nutrients to tissue. Microvascular disease can damage the
eyes (retinopathy), the kidneys (nephropathy) and the nerves (neuropathy).
Instead of viewing these as separate
conditions, researchers suggest in a new review article that they be considered
a potential systemic, or body-wide, dysfunction. The article appeared Thursday
in the American Heart Association journal Arteriosclerosis, Thrombosis,
and Vascular Biology.
Diabetes, along with high blood pressure, can cause large blood
vessels to thicken, narrowing their interior, and small vessels to shrivel or
disappear, said Dr. Joshua Beckman, director of vascular medicine at Vanderbilt
University Medical Center in Nashville, Tennessee. When blood flow is inadequate,
parts of the foot might not be able to heal an injury or parts of the leg may
not survive, he said. If the problem can't be addressed by careful wound care,
or with surgical bypass or angioplasty and possibly stenting, amputation may
follow.
By 2050, an estimated 2.2 million people will
be living with limb loss due to blood vessel impairment. Last summer in the
journal Circulation, scientists including Beckman reported that
among a population of veterans, risk of amputation was 3.7 times higher if microvascular
disease was present, and 14 times higher if peripheral artery disease had been
diagnosed. If a patient had both, risk was 22.7 times higher than in patients
without the conditions. The AHA Strategically Focused Research Network in
Vascular Disease supported the study.
Dr. Marie Gerhard-Herman, associate professor
of cardiovascular medicine at Harvard Medical School in Boston, likens the
vessels involved in peripheral artery and microvascular diseases to a tree. The
tree trunk represents the larger conduit artery affected by peripheral artery
disease, while the smaller leafy branches represent microvessels.
"Clearly the trunk is essential, but also
the small branches are necessary and integral to the tree," said
Gerhard-Herman, who was not involved in the recent research. "There is
higher likelihood of limb loss when the conduit artery to the limb and the
small arteries directly supplying the limb
tissue are both compromised."
Understanding microvascular disease as an
independent contributor to amputations might help explain why they occur even
in patients who had successful surgery to improve blood flow, the researchers
wrote.
The recent findings lend urgency to related
research. Fundamentally, Gerhard-Herman said, scientists still don't understand
what causes microvasculature loss. They also are searching for new therapies to
increase microvascular density and function.
Other research priorities include genetic
studies to learn who is at risk and, physiologically, why. Beckman said his
team is surveying details in medical and genetic records to try to create a
risk score to predict which patients are most likely to need an amputation.
Meanwhile, focusing on intensive foot care
should be a top priority, with doctors checking the feet of at-risk patients at
every office visit, he said. "I would suggest that patients examine their
own feet every day, wear protective footwear at home, and see a podiatrist for
nail care in the setting of PAD or microvascular disease."
Also, doctors caring for people with
cardiovascular risk factors, peripheral artery disease or microvascular disease should provide
guidance about healthy behaviors like quitting smoking and making better food
choices, Beckman said. They also should prescribe medicines that lower risk of
heart attack, kidney failure and limb problems.
In turn, those patients should ask whether
they are getting the most effective medicines, he said, and tell their doctor
if they have peripheral artery disease symptoms such
as burning, aching or other leg discomfort.
Gerhard-Herman advises minimizing microvessel
narrowing by staying warm and avoiding substances that constrict blood vessels,
such as coffee and cigarettes. Also, walking as much as possible will improve
the legs' supply of nutrients, she said.
For patients over age 65, supervised exercise
therapy is covered by Medicare, Beckman said. "The best treatment we have
right now to regrow microvessels is exercise."
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