Fibromuscular Dysplasia, or FMD, is a disease that causes abnormal cell development in the vessel walls of one or more medium-sized arteries in the body. This can cause narrowing (stenosis), aneurysm or a tear (dissection) in the blood vessels. A narrowing or tear causes a decrease in blood flow, which can have various consequences.

Most Affected Arteries
FMD is most commonly found in the arteries that supply blood to the kidneys (renal arteries) and the arteries in the neck and head, which supply blood to the brain. FMD can also be found in the arteries of the liver, spleen or intestines, of the arms and legs, and in the coronary artery of the heart. More than half of people with this condition have FMD in multiple blood vessels. Click here for an image of the vascular system.

What causes FMD?
The cause of FMD is not yet known. Several theories have emerged from research. FMD has been found in several members of the same family, including twins. This is why it is thought that there may be a genetic cause. But a large number of FMD patients have no relatives with FMD. Some FMD patients have a family history of other vascular problems, such as aneurysms.

String of beads
FMD is not caused by cholesterol plaque (atherosclerosis) or inflammation (vasculitis). The layer of the vessel wall (media, intima, or adventitia) in which the abnormal cell development partially occurs determines the severity of the condition. Several types can be found in a patient. Medial fibroplasia is the most common, 80-90%. On an angiography, the affected artery looks like a string of beads.

More women than men?
FMD is more commonly detected in women than in men, leading to the theory that hormones play an important role in the development of the disease. More recent research suggests that the number of men with FMD is greater than was initially realized; however, FMD is less commonly sought in men.

Worldwide research into causes
Other theories about possible causes of FMD include abnormal development of the arteries that supply blood to the artery walls, resulting in an insufficient supply of oxygen; the anatomical position or movement of the artery in the body; certain drugs and smoking. It is possible however that many factors may contribute to the development of FMD. The causes of fibromuscular dysplasia are being researched worldwide.

Who has FMD
FMD is more common in women than in men, although the condition also occurs in men. FMD can occur at any age. In children with FMD, the condition is more often manifested by constriction than by dissections in the arteries. In children, FMD appears to be more common in the renal and intestinal arteries than in the carotid arteries.

How common is FMD?Kralensnoer
It is difficult to determine how often FMD occurs. People with a very mild form of FMD often have no symptoms, so the condition goes undetected. Since the diagnosis of FMD is often made too late and doctors are often unfamiliar with the condition, FMD is probably more common than is realized. It is estimated that 3 to 5% of the US population has FMD. Translated to our country, that is about 680,000 Dutch people.

Other Conditions Associated with FMD
The Ehlers-Danlos vascular subtype (type IV) is associated with the most common form of FMD known as “medial fibroplasia”. This syndrome should be considered in patients with multiple aneurysms and/or dissections in the arteries, in addition to the typical angiographic picture of FMD. There are isolated reports of FMD being associated with other conditions, including Alport’s syndrome, pheochromocytoma, Marfan’s syndrome, and Takayasu’s arteritis. Recent research shows that in patients with FMD, there may be a relationship with other conditions, such as osteoporosis, incipient spinal wear and fibrous dysplasia. Furthermore, in FMD patients, an S-curve is often seen in the internal carotid artery.

Patient stories
Click here for Lucy Raden’s story and here for her blog about climbing the Alpe d’Huez.
Click here for the story of a patient this has happened to.

Interesting links
Below you will find a number of interesting articles (mainly in English) about FMD

Recente Genetisch FMD onderzoeksresultaten Dutch
Recente Genetisch FMD onderzoeksresultaten Engels
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Zeldzame mutaties met functieverlies
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The FMD group Netherlands, in collaboration with prof. dr. P.W. de Leeuw, professor of Internal Medicine at the UMC+ in Maastricht, has created a site where you can find extensive information about FMD.