Fibromuscular dysplasia (FMD) is a condition where the walls of certain arteries develop abnormally, causing them to narrow, bulge, or tear. It most commonly affects the arteries leading to the kidneys and brain, and over 90% of diagnosed patients are women. The mean age at diagnosis is about 56 years, though it can appear at any age.
Unlike the more familiar arterial disease caused by cholesterol plaque buildup, FMD involves structural changes in the artery wall itself. The cells that make up the artery grow irregularly, creating areas of thickening and weakness. This can restrict blood flow, raise blood pressure, or set the stage for more serious vascular events.
Which Arteries Are Affected
FMD most frequently targets the renal arteries (supplying the kidneys) and the carotid and vertebral arteries (supplying the brain). But it isn’t limited to one spot. FMD can show up in arteries throughout the body, and many people have involvement in more than one vascular bed at the same time. That’s why current international consensus guidelines recommend that anyone diagnosed with FMD undergo one-time imaging from the brain to the pelvis, typically with CT angiography or MR angiography, to check for additional areas of disease, hidden aneurysms, or tears in artery walls.
Two Patterns of Disease
FMD comes in two main forms. The more common type, called multifocal FMD, creates alternating areas of narrowing and widening along the artery. On imaging, this produces a distinctive “string of beads” appearance. The less common type, focal FMD, causes a single, tight narrowing in one spot on the artery. The distinction matters because the two types can behave differently and may require different management approaches.
Common Symptoms
What you feel depends largely on which arteries are involved. When the renal arteries narrow, the kidneys sense reduced blood flow and trigger a rise in blood pressure. High blood pressure that’s difficult to control, especially in a younger woman, is one of the classic red flags. When the carotid or vertebral arteries are affected, symptoms can include headaches, dizziness, pulsatile tinnitus (a whooshing sound in your ear that matches your heartbeat), and in more serious cases, transient ischemic attacks or stroke.
Some people have no symptoms at all and are diagnosed incidentally when imaging is done for another reason. Others experience chest pain, shortness of breath, or abdominal pain depending on which arteries are involved. Doctors may also detect an abnormal whooshing sound (bruit) over the neck, abdomen, or flanks during a physical exam.
Serious Complications to Know About
FMD weakens artery walls, making them vulnerable to tearing (dissection) and ballooning (aneurysm). Among female FMD patients who have had brain imaging, roughly 13% have a cerebral aneurysm, a rate significantly higher than the general population. These aneurysms also tend to carry a higher risk of rupture based on their size and location.
FMD is also linked to spontaneous coronary artery dissection (SCAD), a sudden tear in a heart artery that can cause a heart attack. In the U.S. FMD Registry, about 2.7% of patients had a history of coronary dissection. But among FMD patients who had experienced a dissection in any artery, the rate of heart attack history jumped to 15%. This connection between FMD and SCAD is an active area of medical attention, as both conditions disproportionately affect women.
What Causes FMD
The exact cause remains unclear, but genetics play a role. A large study involving over 1,100 FMD patients and nearly 3,900 controls identified a specific genetic variant in a gene called PHACTR1 that increases the risk of developing FMD by about 40%. This same gene variant is also associated with coronary artery disease, migraine, and cervical artery dissection, hinting at shared biological pathways among these conditions.
FMD doesn’t follow a simple inherited pattern where one parent passes it directly to a child. Instead, it appears to involve multiple genetic and possibly environmental factors. The strong female predominance, with men making up 10% or fewer of patients, suggests that hormonal factors may also contribute, though the exact mechanism isn’t well understood.
How FMD Is Diagnosed
Catheter-based angiography, where a thin tube is threaded into the arteries and dye is injected to visualize them on X-ray, remains the gold standard for diagnosing FMD. It can reveal the characteristic string-of-beads pattern or focal narrowing, measure how significantly blood flow is reduced, and even allow treatment during the same procedure.
In practice, most patients are first evaluated with less invasive imaging. CT angiography and MR angiography both perform well, with MR angiography showing sensitivity and specificity of 97% and 93% respectively when compared to catheter-based angiography. MR angiography has the advantage of avoiding radiation and the contrast dye that can be hard on the kidneys, making it a good option for ongoing monitoring. The catheter-based approach is typically reserved for cases where treatment is planned or noninvasive imaging is inconclusive.
Treatment and Management
Treatment depends on the severity of the narrowing and the symptoms it causes. For many people, management starts with blood pressure medication to keep hypertension under control and antiplatelet therapy to reduce the risk of clotting events.
When an artery is severely narrowed, reducing its diameter by more than 70%, a procedure called balloon angioplasty is typically the first choice. During this procedure, a small balloon is inflated inside the narrowed section to widen it. The procedure is considered successful if the narrowing is reduced to less than 30% of the artery’s diameter. If angioplasty doesn’t achieve an adequate result, a stent (a small mesh tube) can be placed to hold the artery open, or in rare cases, surgery may be needed.
For renal artery FMD specifically, angioplasty often improves or even resolves high blood pressure, particularly in younger patients and those who haven’t had hypertension for very long. The longer blood pressure has been elevated before treatment, the less likely it is to fully normalize afterward, which underscores the value of early diagnosis.
Living With FMD
FMD is a chronic condition, but for most people it’s manageable with appropriate monitoring. After initial diagnosis and the recommended brain-to-pelvis imaging screen, follow-up typically involves periodic imaging to watch for progression, new aneurysms, or dissections. Blood pressure monitoring is a routine part of ongoing care.
Because FMD can affect multiple arteries and carries risks like aneurysm and dissection, staying aware of new or changing symptoms is important. A sudden severe headache, new neurological symptoms, unexplained chest pain, or a significant change in blood pressure control all warrant prompt medical attention. Many patients find that connecting with FMD-specific support communities helps them navigate the condition, since it’s uncommon enough that many general practitioners have limited experience with it.