What is Fibromuscular Dysplasia (FMD)?

The word “dysplasia” simply means abnormal cellular development or growth. In people with FMD, the dysplasia involves the walls of one or more arteries in the body.  Areas of narrowing, called stenosis, may occur as a result of abnormal cell development.  If enough narrowing causes a decrease in blood flow through the artery, symptoms may result.  Many people with FMD do not have any symptoms or signs on physical examination and are diagnosed by accident during a radiology scan for another problem.

 FMD is most commonly found in the arteries that supply the kidneys with blood (renal arteries).  Up to 75% of all patients with FMD will have disease in the renal arteries (Fenves, 1999).  The second most common artery affected is the carotid artery, which is found in the neck and supplies the brain with blood.  Less commonly, FMD affects the arteries in the abdomen (supplying the liver, spleen and intestines) and extremities (legs and arms).  More than one artery may have evidence of FMD in 28% of people with this disease (Luscher, 1986).  

 What FMD is NOT…

 Prior to diagnosing a person with FMD, several other diseases should be ruled out.  These include:  arteriosclerosis, commonly referred to as “hardening of the arteries”, inflammatory vascular diseases (vasculitis) such as Takayasu’s arteritis (abnormally dilated arteries).

 What causes FMD?

 The cause of FMD is not yet known, but several theories have been suggested.  A number of case reports in the literature have identified the disease in multiple members of the same family including twins.  As a result it is felt that there may be a genetic cause.  However, a relative may have different artery involvement, different disease severity, or not develop FMD at all.  In fact, not all individuals with FMD have a family member who also has the disease. 

 FMD is also more commonly seen in women than in men resulting in the theory that hormones may play an important role in disease development.  This theory is further supported by the fact that most women are premenopausal at the time of diagnosis.  However, in small population studies, one’s reproductive history (the number of pregnancies and when they occurred) as well as the use of birth control pills did not correlate with the development of FMD.

 Other possible causes of FMD include abnormal development of the arteries that supply the vessel wall with blood resulting in inadequate oxygen supply; the anatomic position of the artery within the body; medications (ergotamine preparations, methysergide); and tobacco use.  It is possible that many factors are involved in the development of FMD.  This area requires further research. 

 What are the signs and/or symptoms of FMD?

 Many people with this disease do not have symptoms or findings on a physical examination. The signs and/or symptoms that a person with FMD may experience depend on the arteries affected and the degree of narrowing within them.  The two most common areas affected by FMD are the renal arteries (arteries carrying blood to the kidneys) and the carotid arteries (arteries carrying blood to the brain).  Any pain or clinical sign related to FMD typically comes from the organ that is supplied by that artery.  For example, FMD in the kidney arteries may cause high blood pressure.  Progression of the disease can also result in ischemic renal atrophy, where some of the kidney’s tissue dies due to lack of oxygen, and in rare circumstances, kidney failure. 

 Patients with impaired carotid arteries may have nonspecific complaints including dizziness, temporary blurring or loss of vision, tinnitus (ringing or buzzing in the ears), vertigo (feeling as if the room was spinning around you), neck pain, and or chronic headaches.  However, a person with severe FMD may have neurologic symptoms involving the facial muscles (drooping of the face, for example), stroke, or transient ischemic attack.  People with carotid FMD have a higher risk for intracranial aneurysms (abnormal dilations of the arteries in the brain).  An intracranial hemorrhage (bleeding in the brain) may occur if an aneurysm ruptures. 

 FMD involving the mesenteric arteries (arteries that supply the intestines, liver and spleen with blood) can result in abdominal pain after eating and unintended weight loss.  FMD in the arms and legs can cause limb discomfort with use, cold limbs, weakness, numbness, or skin changes in the fingers and toes due to lack of blood flow. 

 Who has FMD?

 Anyone can have FMD.  However, it is much more common in women.  Most women are typically diagnosed between the ages of 25-50.  However, some forms of this disease are more common in children or teenagers.   

 How common is FMD? 

 It is difficult to determine how common FMD is in the general population.  This is due to several reasons.  Individuals with mild disease are often asymptomatic and so the disease may go undetected.   Most studies examining the prevalence of FMD have looked at specific patient populations in whom individuals may have already suffered from serious consequences of the disease.  Incidence rates have been quoted at 0.5-1.1% although this may not be indicative of how many people actually have FMD. 

 How can FMD be diagnosed?

 There are a number of methods that can be used to detect FMD.   These include CT scan, MRI, Ultrasound, and Angiogram.  The experience and expertise available at your medical institution will  play an important role in what diagnostic options are available to you. 

 In the most common forms of FMD, a characteristic “string of beads” appearance is seen in the affected artery.  This appearance is due to changes in the cellular tissue of the artery wall that causes the arteries to alternatively become narrow and dilated.  A less common, but more aggressive form of FMD may cause areas of vessel narrowing only without the “string of beads” appearance.

 What kind of treatment is there for FMD?

 There is no cure for FMD.  However, in some cases an attempt should be made to improve the flow of blood through the vessel.  The kind of treatment used for FMD depends largely upon which arteries are affected, the presence and severity of the symptoms, and if there is progression of the disease.   The experience and expertise available at your medical institution will also play an important role in what treatment options are available to you.   Currently, there is not a set protocol for treating FMD. 

 If your health care professionals feel that treatment is warranted, most often percutaneous transluminal angioplasty (PTA) is preferred.  PTA is often performed at the same time as an arteriogram.  Arteriography is a procedure that is performed by a radiologist, vascular surgeon, or a cardiologist with appropriate training that involves inserting a wire into or near the affected artery and injecting contrast material, a dye that can be detected by an X-ray machine.  An x-ray of the affected area is then taken and examined.  If an angioplasty is performed, a catheter is extended into the affected artery and a small balloon is inflated that “stretches” open the vessel.  A metal stent is typically not required to keep the vessel open. 

 The individual is usually awake during the procedure although medications may be given to make the patient more comfortable.  This outpatient procedure usually lasts from one to two hours with a recovery period of up to six hours (this varies widely).  If angioplasty is performed, the procedure and recovery period may be longer.  Occasionally traditional surgery is performed. 

 Most individuals should take an antiplatelet agent daily (i.e., aspirin).  All patients who use tobacco should be encouraged to quit.   The appropriate treatment will vary with each individual and severity of disease.  It should be discussed in depth with a specialist who is very knowledgeable about FMD and its natural history.    

 FMDSA Frequently Asked Questions were authored by Susan M. Begelman, M.D., Staff Physician, The Cleveland Clinic Foundation.  Updated August 2, 2004.

 

BIBLIOGRAPHY

Begelman, SM and Olin, JW.  Fibromuscular Dysplasia,  Current Opinion in Rheumatology.  (2000) 12:41-47.

Fenves, AZ and Ram, CV.  Fibromuscular Dysplasia of the Renal Arteries, Current Hypertension Reports.  (1999) 1:546-549. 

Lusher, TF, Keller HM, Imhof, HG, Griminger, P, Kuhlmann, U, Largiader, F, Schneider, E, Schneider, J, Vetter, W.  Fibromuscular Hyperplasia: Extension of the disease and therapeutic outcome.  Results of the University Hospital Zurich Cooperative Study on Fibromuscular Hyperplasia.   Nephron.  (1986).  44(Suppl 1): 109-114. 

Lusher, TF, Lie, JT, Stanson, AW. Houser, OW, Hollier, LH, and Sheps, SG.    Arterial Fibromuscular Dysplasia, Mayo Clinic Proceedings.  (1987) 62: 931-952.