What is fibromuscular dysplasia?

Fibromuscular dysplasia (FMD) is a rare blood vessel disorder in which some of the strong, flexible cells of arteries are replaced with cells that are more fibrous. Fibrous cells are less strong and also less flexible. This change in composition of the arteries leads to their becoming stiffer and more prone to damage. FMD can lead to high blood pressure, stenosis, aneurysm and sometimes dissection of arteries.

FMD is different from most other vascular diseases because it does not involve inflammation or plaque. Many vascular problems are caused by atherosclerosis, a buildup of fatty plaque inside the arteries that hardens and narrows them, reducing blood flow and sometimes leading to aneurysm or dissection. FMD, on the other hand, is a disease of the artery walls that can exist even when there is no plaque buildup.

How are arteries constructed?

Arteries are made of three main layers:

• Tunica intima means “inner coat” or inner layer, which comes in direct contact with the blood as it flows.
• Tunica media means “middle coat” and is the thickest layer. It is made of smooth muscle cells and elastic fibers, allowing the artery to stretch without breaking as blood pulses through.
• Tunica externa (sometimes called adventitia) means “outer coat” and surrounds the artery with elastic fibers as well as collagen, a gluey fiber that allows arteries to stick in place.

What are the effects of fibromuscular dysplasia?

A healthy, elastic artery responds to the rhythmic movement of blood by expanding and contracting as blood pulses through it. An artery affected by FMD may be too stiff — or not stiff enough. If overly stiff, the artery will be unable to expand as blood rushes through it, leading to high blood pressure. If not stiff enough, the artery can balloon or dilate, leading to an aneurysm. In one common form of FMD, the tunica media alternates between these two states, causing the affected area to look like a string of beads: wide, then narrow, then wide again, then narrow again, etc.

Where does fibromuscular dysplasia occur?

While FMD can be found in any location of the body, the most common areas are the renal arteries (leading to the kidneys) and the carotid and vertebral arteries in the neck that lead to the brain. Much less commonly, the mesenteric (digestive system) arteries may be involved.

FMD often manifests in more than one place.

What causes fibromuscular dysplasia?

Not much is known about the causes of FMD.

• FMD may be found in children.
• A portion of cases are thought to be genetic.
• FMD may be related to hormones, as a high percentage of people diagnosed with FMD are women of childbearing age.
• Research is ongoing at Johns Hopkins and elsewhere to help understand the causes of FMD.

What are the symptoms of fibromuscular dysplasia?

FMD may cause no symptoms at all. When symptoms do occur, they will vary depending on the type and location of fibromuscular dysplasia. Symptoms include:

• Headache or migraine
• Pulsatile tinnitus, a ringing or swishing sound in the ears that occurs with the heartbeat
• Neck pain in the case of carotid artery dissection

The presence of certain conditions may also suggest FMD, especially when the usual causes for these conditions, such as atherosclerosis, inflammation and older age, are absent. Conditions include:

• Hypertension (high blood pressure), especially resistant hypertension, in a person younger than 35
• Sudden-onset hypertension or a sharp rise in blood pressure when it was previously well controlled
• A bruit (whooshing sound over an artery) in the neck or abdomen
• Stroke or transient ischemic attack (TIA), especially in someone young and/or without atherosclerosis
• Spontaneous coronary artery dissection (SCAD), especially in a woman who has just given birth

How is fibromuscular dysplasia diagnosed?

Because FMD can have no symptoms, many people learn they have the condition as the result of an angiogram or other medical test done for another reason. For some, the condition may not even be diagnosed until they suffer an aneurysm, dissection or other critical event.

To confirm a diagnosis of fibromuscular dysplasia, your doctor may order some combination of the following:

• Computed tomography angiography (CTA)
• Duplex ultrasound
• Magnetic resonance angiography (MRA)
• Digital subtraction angiography (DSA)

How is fibromuscular dysplasia managed?

Although FMD has no cure, the conditions caused by FMD can and should be treated, especially high blood pressure.

FMD is best managed by specialized physicians who have experience in the condition. FMD is a “look-alike” disease that results in conditions often caused by other factors. It has its own, separate best practices for medications and procedures. Among the approaches a physician may recommend are:

• Medications, such as aspirin, to prevent blood from clotting
• Annual imaging studies, such as CTA or MRA
• Lifestyle changes, such as:
  • Quitting smoking
  • Cutting down on salt
  • Daily exercise