What is Fibromuscular Dysplasia
(FMD)?
FMD
is a disease of blood
vessels that causes narrowings (stenosis)
and balloonings (aneurysms).
It is different to atherosclerosis,
or "hardening of the arteries". There is no inflammation
of arteries, which distinguishes it from vasculitis,
where inflammation is present.
Five pathological subtypes of FMD
have been described. By far the commonest is "medial fibroplasia", which
usually produces alternate narrowing and ballooning, the classic "string
of beads" appearance on angiography.
Which arteries are affected?
Involvement of the kidney
arteries is most commonly recognised, usually because of the development
of high blood pressure. The arteries
to the brain and the legs are also commonly affected. Less commonly,
involvement of the arteries to the bowel and the heart may be apparent.
Who does FMD
affect?
FMD
affects women three times as often as men. The most common age at diagnosis
is between 30 and 50 years, however, any age may be affected.
How common is FMD?
Disease of the kidney arteries
accounts for between 1-in-50 and 1-in-20 cases of high blood pressure seen
at high blood pressure clinics, and for up to 1-in-5 children with high
blood pressure. FMD
is the most common kidney artery disease causing high blood pressure in
patients younger than 40.
Estimates of how common FMD
is
depend upon the way it is looked for. FMD
has been found in 1-in-50 to 1-in-8 people with normal blood pressure,
and approximately 1-in-10 patients undergoing investigation for underlying
causes of high blood pressure. FMD
may, therefore, be more prevalent than previously appreciated, and almost
certainly remains undiagnosed in less severely affected patients.
How may FMD
present?
FMD
predominantly affects young females and can lead to high blood pressure
and stroke. FMD
is frequently not detected until damage to organs has occurred, so that
shrinkage of the kidney is unfortunately often present at diagnosis. Interference
with blood circulation to the brain, legs or bowel may also produce symptoms.
With increasing age, atherosclerosis becomes the most common cause of these
symptoms.
How is FMD
diagnosed?
FMD
may be suspected in patients, particularly young patients, presenting with
any of the problems mentioned above. Blood flowing through narrowed arteries
produces turbulence which may be heard with a stethoscope. This is called
a bruit. Ultrasound
scans can detect turbulence and changes in blood flow in a wide range
of arteries. Nuclear (or radioisotope
scans) of the kidneys may show reduced or delayed blood flow to one
or both kidneys. All of these can indicate that there is a narrowing of
an artery, however, only angiography
(the injection of dye into the artery) can definitely diagnose FMD.
The most common lesion is the multifocal lesion, consisting of alternating
narrowings and widenings of the artery producing a "string of beads" appearance.
Less commonly, lesions may appear as focal (short, single) or tubular (long
narrowings of even diameter).
How is FMD
treated?
The first step is to determine
if FMD is responsible
for the presenting problem. For example, a patient may have high blood
pressure and FMD,
but not high blood pressure caused by FMD.
In a patient with high blood pressure, the measurement of renin levels
in the veins draining the kidneys is essential in determining the relationship
of the FMD to
high blood pressure. The results of all tests together with the patient's
blood pressure level, any effects of the blood pressure on the heart, and
any other medical conditions are all considered. If treatment is indicated,
angioplasty,(News)
where a balloon is inflated
inside the artery to open it up, is the preferred and usual treatment.
If, as is rarely the case, the lesionis
not suitable for angioplasty, an operation may be possible and recommended.
What causes FMD?
At this stage, the cause of FMD
is unknown.(Medical journals) The following
facts are known and may provide clues to the cause:
-
Females are most frequently affected
-
The most common age for diagnosis is
between 30 and 50 years
-
In the kidney arteries, involvement
is most often on the right or bilateral
-
Several arteries may be affected in
the one patient
-
More than one member of a family may
be affected.
FibroMuscular Dysplasia.
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