Fibromuscular dysplasia (FMD) is a condition where the walls of certain arteries develop abnormally, causing them to narrow, bulge, or form a beaded pattern. It most commonly affects the arteries leading to the kidneys and brain, and about 85% of people diagnosed are women. FMD is not caused by inflammation or plaque buildup like atherosclerosis. Instead, the cells within the artery wall itself grow irregularly, changing the shape of the vessel and restricting blood flow.
How FMD Affects Your Arteries
Healthy arteries have smooth, flexible walls made up of three distinct layers. In FMD, one or more of these layers develops abnormal cell growth, which distorts the artery’s shape. The most common pattern, called multifocal FMD, creates alternating areas of widening and narrowing along the artery. On imaging, this looks like a “string of beads.” A less common form, focal FMD, produces a single tight narrowing in one spot.
These changes reduce the artery’s ability to deliver blood efficiently. Depending on which artery is involved, the downstream organ (usually a kidney or part of the brain) receives less blood than it needs. That mismatch between supply and demand is what drives most of FMD’s symptoms.
Who Gets FMD
In an analysis of over 4,500 cases in the United States, 85% of patients were female, about 80% were Caucasian, and roughly half were adults between 18 and 65 at the time of diagnosis. FMD can also occur in children and older adults, though it’s less commonly identified in those groups. The condition was once thought to be rare, but improved imaging technology has made it easier to detect, and prevalence estimates have risen over the past two decades.
There is a genetic component. Researchers have confirmed an association between FMD and a variant in a gene called PHACTR1, which plays a role in how cells regulate their internal structure. But no single gene causes FMD on its own. The pattern of inheritance is complex, likely involving multiple genetic and environmental factors that aren’t fully understood yet.
Kidney Artery FMD and High Blood Pressure
The most classic presentation of FMD is high blood pressure caused by narrowing of one or both renal arteries. When less blood reaches the kidneys, they interpret it as a drop in overall blood pressure and activate a hormonal system designed to raise it. The kidneys release signals that cause blood vessels throughout the body to tighten and prompt the body to retain salt and water. The result is genuinely elevated blood pressure, sometimes severe, in a person who may otherwise seem too young or healthy for it.
This type of high blood pressure often doesn’t respond well to standard lifestyle changes. It may require specific medications that block the kidney’s pressure-raising hormones. In some cases, low potassium levels show up on blood work because the same hormonal cascade causes the body to excrete too much potassium. Actual kidney damage from FMD is uncommon, which distinguishes it from other causes of restricted kidney blood flow.
Symptoms Involving the Head and Neck
When FMD affects the carotid arteries (the major vessels running up each side of the neck toward the brain), it can cause a distinct set of neurological symptoms. According to data from the US Registry for Fibromuscular Dysplasia, which tracked over 2,600 patients, 37% reported pulsatile tinnitus, a rhythmic whooshing sound in the ear that matches the heartbeat. This was one of the most common symptoms at the time of diagnosis.
Patients with pulsatile tinnitus were also significantly more likely to experience headaches (82.5% vs. 62.7% of those without it), dizziness (44.9% vs. 22.9%), and neck pain (41.3% vs. 19.4%). A cervical bruit, an abnormal whooshing sound a doctor can hear through a stethoscope placed on the neck, was found in about 37.5% of patients with pulsatile tinnitus. Younger women were especially likely to present with this symptom cluster.
FMD in the carotid arteries also raises the risk of arterial dissection, where the inner lining of the artery tears and blood seeps between the layers of the vessel wall. About 19% of patients with pulsatile tinnitus had experienced a cervical artery dissection. In rare cases, FMD of the head and neck arteries can lead to transient ischemic attacks or stroke, particularly in younger adults who wouldn’t typically be at risk.
The Link to Spontaneous Coronary Artery Dissection
FMD has a strong and well-established connection to spontaneous coronary artery dissection (SCAD), a sudden tear in the wall of a heart artery that can cause a heart attack, often in otherwise healthy young women. Studies have found FMD-type changes in other arteries in anywhere from 25% to 86% of SCAD patients, depending on how thoroughly they were screened. The prevalence of FMD among SCAD patients may be as high as 45%, making it the most commonly associated condition.
This overlap suggests a shared vulnerability in the artery walls. If you’ve been diagnosed with SCAD, your doctors will typically screen you for FMD in other vascular beds. The reverse is also true: people with known FMD may be monitored for signs of coronary artery problems.
How FMD Is Diagnosed
FMD is often discovered incidentally, during imaging done for another reason, or after a doctor investigates unexplained high blood pressure in a younger patient. The gold standard for diagnosis is catheter-based angiography, where a thin tube is threaded into the artery and contrast dye is injected to create detailed images. This provides the clearest view of the characteristic beaded pattern or focal narrowing.
In practice, most initial evaluations use less invasive imaging: CT angiography, MR angiography, or duplex ultrasound. These can often identify FMD, especially the multifocal “string of beads” type, without requiring a catheter procedure. However, catheter-based angiography remains the definitive test when noninvasive results are unclear or when a procedure to treat the narrowing is planned at the same time.
Because FMD frequently affects more than one artery, a European and US expert consensus recommends imaging multiple vascular territories once FMD is found in one location. Someone diagnosed with renal artery FMD, for example, would typically also be screened in the head and neck arteries.
Treatment and What to Expect
Managing FMD depends on which arteries are affected and how severe the symptoms are. For renal artery FMD causing high blood pressure, medications that block the kidney’s pressure-raising hormone system are the first-line treatment. Many people achieve good blood pressure control with medication alone.
When medication isn’t enough, or when the narrowing is severe, a procedure called balloon angioplasty can widen the artery. A small balloon is inflated inside the narrowed segment to stretch it open. Unlike procedures for atherosclerosis, stents are generally not placed for FMD because the artery wall responds well to simple stretching. Recovery from angioplasty is relatively quick, typically involving a short hospital stay and a few days of limited activity.
For FMD in the carotid or other head and neck arteries, treatment focuses on preventing complications like dissection or stroke. This often involves antiplatelet therapy to reduce clotting risk. Surgical or catheter-based interventions in these arteries are reserved for more severe cases, such as significant narrowing that’s causing symptoms or recurrent dissections.
FMD is a chronic condition, but for most people it progresses slowly or remains stable over time. Regular imaging follow-up, typically every one to two years, helps track whether the affected arteries are changing. Many people with FMD live normal, active lives once their blood pressure is controlled and their vascular health is being monitored.