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Fibromuscular Dysplasia (FMD)

What is fibromuscular dysplasia?

FMD also can affect the arteries to the legs or, less frequently, arteries in other parts of the body. In many cases, FMD affects multiple arteries of the body.

Who is affected by FMD?

FMD is most common in women between ages 30 and 50, but FMD also may occur in children and the elderly, in some cases. FMD occurs two to 10 times more frequently in women than in men.

What causes FMD?

The causes of FMD are still unknown and are the focus of considerable research. The disease most likely has multiple underlying causes. Some of the factors that may play a role include:

  • Hormonal influences: The disease occurs most commonly in women.
  • Genetics: About 10 percent of cases are familial (inherited). FMD may also occur with other genetic abnormalities the affect the blood vessels.
  • Internal mechanical stress, including trauma or stress to the artery walls.
  • Loss of oxygen supply to the blood vessel wall: This occurs when the tiny blood vessels in the artery walls that supply them with oxygenated blood get blocked by fibrous lesions.

Types of fibromuscular dysplasia

Medial Fibroplasia

Figure 1: Fibromuscular dysplasia of the right renal artery. The classic “beads on a string” appearance is typical of medial fibroplasia, the most common type of FMD. In this case, there is mild to moderate narrowing of the artery.

Intimal Fibroplasia

Figure 2: Fibromuscular dysplasia of the right renal artery. The smooth, concentric narrowing (arrow) has the typical appearance of intimal fibroplasia. In this case, there is severe narrowing of the artery, and the patient was treated with balloon angioplasty.

Artery walls have three layers:

  • Tunica Intima (the inside layer)
  • Tunica Media (the middle layer)
  • Adventitia (the outside layer)

Fibromuscular dysplasia is described in terms of the affected arterial layer and the composition of the lesions. Depending on the type of FMD, the narrowing (stenosis) of the artery is caused by an excess of either the fibrous or muscular components of the arterial wall.

While the type of FMD can only be determined with 100 percent accuracy by analyzing the artery wall under the microscope, such as after a biopsy or surgical procedure, this is rarely done.

In most cases, it is possible to distinguish the type of FMD based on the appearance of the arteries affected with a dye angiogram test.

The five types of dysplasia, from most common to least common, are:

Medial fibroplasia
  • 75 to 80 percent of FMD lesions are this type
  • Affects the tunica media
  • Characterized by areas of fibrous lesions alternating with bulging areas (aneurysms)
  • Has a classic “beads on a string” appearance on a dye angiogram (see Figure 1)
Intimal fibroplasia
  • Less than 10 percent of FMD lesions are this type
  • Caused by collagen (fibrous tissue) deposits around the inside layer of the artery wall, the tunica intima
  • Concentric, smooth narrowing (without beads) appearance on a dye angiogram (see Figure 2)
Perimedial fibroplasia
  • Less than 10 percent of FMD lesions are this type
  • Extensive collagen deposits in the outer portion of the tunica media
  • Irregular thickening of the artery walls
  • Has a different "beads on a string" appearance than medial fibroplasia, with beads that have a small diameter compared to the normal artery
  • Increases the risk for total blockage of affected arteries
Medial hyperplasia
  • 1 to 2 percent of lesions are this type
  • Caused by excessive formation of smooth muscle cells
  • Fibrous deposits are absent
  • Appearance on angiogram similar to intimal fibroplasia
Periarterial hyperplasia
  • Rare: Fewer than 1 percent of FMD cases are this type
  • Caused by expansion of the adventitia
  • Collagen extends into the surrounding fat layers
  • Characterized by inflammation of the artery and surrounding area

What are the symptoms of FMD?

Many people with FMD do not have any symptoms, but symptoms can occur if the stenosis is severe enough to restrict blood flow through the affected artery.

Symptoms of moderate FMD in the carotid artery may include headaches, ringing or “swishing” noise in the ears or lightheadedness. More advanced cases of FMD can cause stroke or a transient ischemic attack (TIA).

FMD of the carotid or vertebral arteries (that supply blood to the back of the brain) may occur with a tear in the artery, known as carotid dissection. Symptoms of carotid dissection include headache, sudden neck pain, along with symptoms of stroke or TIA in severe cases.

FMD of the renal arteries frequently causes high blood pressure in these arteries (renovascular hypertension) and/or diminished kidney function (renal insufficiency). FMD usually does not progress to kidney failure.

How is FMD diagnosed?

FMD is often diagnosed when the person is having an X-ray or scan for another problem, and the beaded appearance in the arteries is identified.

In other cases, a patient may be diagnosed with FMD after the physician hears a bruit (swishing noise indicating abnormal flow) in the neck or abdomen during a routine physical examination.

When a patient is diagnosed with FMD in one part of the body, additional imaging studies may be obtained to evaluate the other blood vessels. For example, if a patient has carotid FMD and has high blood pressure, a test to evaluate the renal arteries may be performed.

Non-invasive imaging studies such as duplex ultrasound, magnetic resonance angiography (MRA) and computed tomography angiography (CTA) can be used to confirm the diagnosis of FMD and determine the extent of the lesions.

In some cases, it is recommended that the patient undergo a dye angiogram, which is considered the standard for diagnosing FMD. In general, dye angiogram studies are performed only when the diagnosis of FMD is not clear, or when the patient may require a therapeutic procedure during the dye angiogram, such as a balloon angioplasty.

It is generally recommended that patients diagnosed with carotid or vertebral artery FMD undergo an imaging study of the blood vessels in the brain to exclude the presence of an intracranial aneurysm that may require additional treatment.

What treatments are available for FMD?

Medications

When FMD is present without any symptoms, it usually is benign and does not require intervention. For these patients, the physician may prescribe an antiplatelet medication to prevent blood clots. The antiplatelet medication may be prescribed, or your physician may recommend that you take aspirin on a regular basis.

Patients with renovascular hypertension as a result of FMD may be treated with blood pressure medications, particularly with an angiotensin converting enzyme inhibitor (ACE-inhibitor).

Identify and Treat Risk Factors

Risk factors for vascular disease, such as high blood pressure, diabetes and high cholesterol, should be evaluated and treated. Patients with these conditions should have an imaging study (duplex ultrasound, MRA or CTA) performed at regular intervals, generally every year, to monitor disease progression. This is particularly important when an aneurysm is present in the internal carotid arteries or the patient has had a carotid or vertebral artery dissection.

Angioplasty

In certain cases, percutaneous angioplasty of the renal arteries is recommended. Similar to the procedure used to treat blockages in the heart arteries, renal angioplasty involves placement of a balloon-mounted catheter inside the artery at the site of the narrowing or blockage. The catheter is guided through the blood vessel with the aid of a special x-ray machine.

The balloon is inflated to re-open the blood vessel, and then the balloon and the catheter are withdrawn.

Placing a stent (small, metal mesh tube) at the site of the blockage has not been proven to improve the efficacy of the renal angioplasty procedure and does not increase the longevity of the procedure results. In general, renal artery stents should only be placed when the results of angioplasty alone are not adequate to improve blood flow to the kidney.

Angioplasty also is recommended for patients with FMD of the internal carotid artery who experience TIAs or stroke related to severe arterial narrowing. Stenting may be necessary in rare cases, when patients with FMD have had carotid or vertebral artery dissection or who have a carotid aneurysm.

Surgery

Reconstructive surgery may be recommended for patients with complex FMD of the renal arteries or with an aneurysm of the internal carotid or vertebral arteries. Surgery depends upon the location and the extent of disease, but generally involves removing or bypassing the affected portion of the artery to restore normal blood flow.

FMD is a very different disorder than atherosclerosis (the plaque formation that is the most common cause of blocked arteries). Angioplasty and reconstructive surgery are technically demanding procedures and should be performed only by a physician experienced in these procedures and in the care of patients with FMD.

Resources and References

FMD Clinic

Cleveland Clinic provides specialized care for patients with fibromuscular dysplasia in the FMD Clinic. Care is provided by vascular medicine specialists who collaborate with a multi-disciplinary team, including interventional cardiologists, vascular surgeons, nephrologists, geneticists and neurologists. Your health care team will work with you to develop a treatment plan tailored to your needs and condition.

Reviewed: 04/14

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This information is provided by Cleveland Clinic and is not intended to replace the medical advice of your doctor or health care provider. Please consult your health care provider for advice about a specific medical condition.

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