What is fibromuscular dysplasia (FMD)?

Fibromuscular dysplasia is a disease of the wall of medium-sized arteries, not related to atherosclerosis (cholesterol deposits) or inflammation. Typically, it may be at the origin of arterial narrowing (stenosis). It may also cause dilation (aneurysm), a tear (dissection) or tortuosity of the affected arteries.

FMD lesions are more commonly seen in the renal or cerebrovascular (head and neck) arteries but may also affect all medium-sized arteries (digestive, brain and arms/legs).
FMD can also be at the origin of Spontaneous Coronary Artery Dissection (SCAD – dissection in the artery/arteries of the heart). Finally, aortic involvement is possible, although it is more often seen in cases of focal FMD, particularly in children.

A stenosis or dissection may cause symptoms connected to a reduction in blood flow. Symptoms depend on which artery or arteries are affected (see “symptoms” section). A ruptured aneurysm could cause internal bleeding with serious consequences. However, there are many patients with FMD who have no symptoms or signs found during medical examination. In these cases, FMD may be found on the occasion of imaging (CT- or MR-angiography) carried out for another reason.

Who is affected?

FMD is seen more commonly in women than men. It is typically diagnosed in middle-aged, white, hypertensive women. However, FMD can be diagnosed in women and men from all ethnicities, at any age, from childhood through to old age.

Is FMD a common disease?

The prevalence of FMD in the general population is difficult to establish, as less seriously affected arteries may not provoke symptoms, so the disease can remain undetected and therefore undiagnosed.
The diverse range of symptoms (depending on which arteries are affected) complicates studies on how prevalent the disease actually is. Figures based on renal artery imaging of candidate kidney donors found a prevalence of 3-4% of affected renal arteries with no symptoms present.
FMD of the cerebrovascular arteries is found as frequently as renal artery involvement.

What are the causes of FMD?

Environmental and genetic causes are considered to play a role, but the causes remain largely unknown and are the subject of ongoing intensive research.

What are the signs and symptoms of FMD?

Many people affected by FMD have no discernable symptoms, or signs that are detected during medical examination. When there are signs and symptoms of FMD, they depend on the arteries that are affected and the organs those arteries serve, as well as on the severity and type of the FMD lesions (stenosis, dissection, aneurysm).
FMD-related stenosis (narrowing) of the renal arteries can be the cause of hypertension. FMD of the neck arteries (carotid/vertebral) may be discovered following migraine or pulsatile tinnitus (a whooshing sound in the ear).
Even in the absence of any symptoms, it may be possible for a doctor to suspect FMD if a vascular “bruit” (vascular murmur) is detected by auscultation (listening with a stethoscope).

How is FMD diagnosed?

Diagnosing FMD relies on medical imaging. The preferred imaging modality when FMD is suspected is CT-angiography (CTA) or MR-angiography (MRA), if CTA is contraindicated.
Duplex ultrasound as a first-line diagnostic test may be an alternative in specialized centres with a large experience.
Once a diagnosis is established duplex ultrasound can be useful, particularly in the follow up of renal artery FMD.

Is there a treatment for FMD?

Currently, there is no cure for FMD. However, FMD can be adequately managed with the objective of alleviating symptoms and preventing complications. The type of treatment proposed depends on the symptoms experienced, the clinical manifestations as well as the severity, location and extent of the FMD lesions. The management/treatment should be discussed with a specialist with experience of following FMD patients, preferably within an experienced multidisciplinary team.