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Fibromuscular dysplasia (FMD) is a non-atherosclerotic, non-inflammatory vascular disease in which at least one of your arteries has an abnormal cluster of cells growing in the artery wall. This cluster causes the artery to narrow (stenosis), such as arteries in the kidneys (renal artery), arteries to the brain (carotid artery/vertebral artery) and less commonly the arties that supplies the abdomen (abdominal aorta), which can cause damage to the organs that, receive blood through the narrowed artery. FMD is so poorly understood by many healthcare providers, treatment is often not optimal, leading to impaired quality of life and potential serious number of complications, such as hypertension, stroke, myocardial infarction (heart attack), aneurysms (arterial swelling) and arterial dissection, if left untreated.A few thousand cases have been confirmed in the U.S., but some experts believe it affects up to 5% of the population. When presumably healthy kidney donors are screened with X-rays, FMD has been found in close to 4%. In individuals with FMD, the cells in the walls of the arteries undergo abnormal growth. As a result, the inner passage of the vessels may become narrowed. This can cause symptoms if the blood flow is decreased enough. However, FMD is often diagnosed incidentally in the absence of any signs or symptoms during an imaging study. When the vessel is filled with dye for an X-ray, it will show a characteristic “string of beads” appearance.
What is DysplasiaThe word “dysplasia” simply means abnormal cellular development or growth.
What is Arterial DissectionArterial dissection refers to a tear within the wall of a blood vessel (tunica media), which allows blood to separate the wall layers, creating a pseudoaneurysm (dissecting hematoma).
A pseudoaneurysm, also known as a false aneurysm, is a hematoma (localized swelling filled with blood) that forms as the result of a leaking hole in an artery. Note that the hematoma forms outside the arterial wall, so it is contained by the surrounding tissues. Also it must continue to communicate with the artery to be considered a pseudoaneurysm. This must be distinguished from a true aneurysm, which is a localized dilatation of an artery including all the layers of the wall. A pseudoaneurysm is also different from an arterial dissection, which is a separation of the layers the arterial wall, and may be associated with later aneurysm formation. The most common location for a true left ventricular aneurysm involves the apex of the heart.
What causes FMDThere is a very strong likelihood that there is a genetic basis for the development of FMD but not all individuals with FMD have a family member with the disease. Other possible causes of FMD include abnormal development of the arteries that supply the vessel wall with blood resulting in inadequate oxygen supply; the anatomic position of the artery within the body and tobacco use. It is likely that many factors are involved in the development of FMD. This area requires further research.
Genetic Prevalence of FMDFibromuscular dysplasia is an autosomal dominant disorder. It tends to occur between 14 and 50 years of age, but it has also been found in children younger than age 14. In one study, women are affected more often than men.
Angiographic & Pathological Types
There are three major types of FMD:
- Medial dysplasia
- Intimal fibroplasia
- Adventitial (periarterial) fibroplasia.
Although this classification system was initially developed for renal artery stenosis, it can be applied to all arteries. Medial dysplasia can itself be divided into three subgroups:
- Medial fibroplasia
- Perimedial fibroplasia
- Medial hyperplasia
Medial fibroplasia is the most common form (accounting for 80–90% of all types of FMD) and is characterized by a ‘string of beads’ appearance on angiography. The size of the ‘beads’ usually exceeds that of the artery and involves the medial layer in the mid-to-distal portion of the vessel.
Fibromuscular dysplasia is characterized by fibrous thickening of the intima, media, or adventitia of the artery. Up to 75% of all patients with FMD will have disease in the renal arteries. The lesions cause narrowing of the artery lumen. The second most common artery affected is the carotid artery, which is found in the neck and supplies the brain with blood. Less commonly, FMD affects the arteries in the abdomen (supplying the liver, spleen and intestines) and extremities (legs and arms). More than one artery may have evidence of FMD in 28% of people with this disease. All arteries should be checked if found.
Signs and Symptoms
FMD of Renal Arteries (Kidney):
- High blood pressure
- Abnormal kidney function as detected on blood tests
- Flank pain from dissection or infarction of the kidney
- Kidney failure (rare)
- Shrinkage (atrophy) of the kidney
FMD of Carotid Arteries:
- Bruit (noise) heard in neck with stethoscope
- Swooshing sound in ear
- Ringing of the ears
- Vertigo (room spinning)
- Transient ischemic attack (TIA)
- Neck pain
- Horner’s syndrome
- Arterial Dissection
People with carotid FMD have a higher risk for intracranial aneurysms (abnormal dilations of the arteries in the brain). An intracranial hemorrhage (bleeding in the brain) may occur if an aneurysm ruptures. FMD involving the mesenteric arteries (arteries that supply the intestines, liver and spleen with blood) can result in abdominal pain after eating and unintended weight loss. FMD in the arms and legs can cause limb discomfort with walking or arm use (intermittent claudication), cold limbs, weakness, numbness or pain.NOTE: Horner’s syndrome is a pattern of symptoms occurring as a result of damage to the nerves in the cervical region of the spine (drooping eyelids and constricted pupils and absence of facial sweating).
How can FMD be DiagnosedThere are a number of methods that can be used to detect FMD. These include computed tomographic angiography (CTA) and magnetic resonance angiography (MRA), ultrasound, and catheter based angiogram. The experience and expertise available at your medical institution will play an important role in what diagnostic options are available to you. In the most common form of FMD (medial fibroplasia), a characteristic “String of Beads” appearance is seen in the affected artery. This appearance is due to changes in the cellular tissue of the artery wall that causes the arteries to alternatively become narrow and dilated. A less common, but more aggressive form of FMD may cause an area of severe concentric narrowing of the blood vessel (intimal fibroplasia) or long smooth narrowing.
There is no cure for FMD. However, in some cases an attempt should be made to improve the flow of blood through the vessel. The kind of treatment used for FMD depends largely upon which arteries are affected and the presence and severity of the signs or symptoms. If your health care professionals feel that treatment is warranted, most often percutaneous transluminal angioplasty (PTA) is preferred. PTA is often performed at the same time as an arteriogram. Arteriography is a procedure that is performed by a vascular specialist (interventional radiologist, neuroradiologist, vascular surgeon, vascular medicine specialist or cardiologist) with appropriate training. It involves inserting a small tube into or near the affected artery and injecting contrast material, a dye that can be detected by an X-ray machine. An x-ray of the affected area is then taken and examined. If an angioplasty is performed, a catheter is extended into the affected artery and a small balloon is inflated that opens the vessel in the area of narrowing. A metal stent is typically not required to keep the vessel open and under most circumstances should only be used if angioplasty alone was not successful or to treat a dissection (tear) of the artery.
Most individuals should take an antiplatelet agent daily (i.e., aspirin). All patients who use tobacco should be encouraged to quit. The appropriate treatment will vary with each individual and severity of disease. It should be discussed in depth with a specialist who is knowledgeable about FMD.