Fibromuscular dysplasia (FMD) is a vascular disease characterized by abnormal cell development in the walls of arteries. This condition is not caused by inflammation or the buildup of plaque, which distinguishes it from atherosclerosis. The abnormal cellular growth makes the arteries stiffer and less flexible, leading to potential problems like narrowing (stenosis), bulging (aneurysm), or tearing (dissection). FMD primarily affects the medium-sized arteries in the body and is most frequently identified in individuals between 40 and 60 years old.
Affected Arteries and Resulting Symptoms
The symptoms of fibromuscular dysplasia are directly linked to which arteries are affected and the extent of restricted blood flow. Many individuals with FMD may not experience any symptoms, especially in mild cases. When symptoms do appear, they vary widely depending on the location of the abnormal artery.
The arteries supplying blood to the kidneys, the renal arteries, are among the most commonly affected. When FMD narrows these arteries, it can cause high blood pressure (hypertension). This specific type of high blood pressure is known as renovascular hypertension. Over time, reduced blood flow can also impact kidney function.
Another frequent site for FMD is the carotid and vertebral arteries, which are located in the neck and supply blood to the brain. FMD in these arteries can lead to a range of neurological symptoms. Patients may experience headaches or migraines, neck pain, and a pulsing or whooshing sound in the ears synchronized with their heartbeat, a phenomenon called pulsatile tinnitus. Dizziness is also a common complaint.
In some instances, the abnormal artery structure in the carotid or vertebral arteries can lead to more severe events. The tearing of an artery wall, known as a dissection, can disrupt blood flow to the brain, potentially causing a stroke or a transient ischemic attack (TIA). While less common, FMD can also affect arteries in the abdomen, arms, and legs, leading to symptoms specific to those areas.
Causes and Risk Factors
The precise cause of fibromuscular dysplasia remains unknown, but research points toward several contributing factors. The condition is not fully understood, but evidence suggests a combination of genetic and environmental influences may play a role in its development.
A strong hormonal connection is suspected, largely because FMD predominantly affects women. More than 90% of diagnosed cases occur in females, with many being of childbearing age, which suggests that female hormones may be involved in the abnormal development of the artery walls. However, the exact mechanism behind this hormonal link is still under investigation.
A genetic predisposition also appears to be a factor. While specific genes have not been definitively identified, there is evidence that FMD can run in families. Having a close relative with the condition may increase an individual’s risk of developing it.
Diagnosis Process
Diagnosing fibromuscular dysplasia typically begins after a patient presents with symptoms like difficult-to-control high blood pressure or pulsatile tinnitus, or it may be found incidentally during medical imaging performed for other reasons. A physician may initially hear an abnormal swishing sound, called a bruit, when listening with a stethoscope to blood flow in the neck or abdomen. This finding often prompts further investigation into the condition of the arteries.
To confirm a diagnosis, doctors rely on advanced imaging tests that visualize the arteries. Common non-invasive methods include CT angiography (CTA) and MR angiography (MRA), which use specialized computer processing and magnetic fields, respectively, to create detailed images of the blood vessels. A duplex ultrasound may also be used, which combines traditional ultrasound with Doppler technology to assess blood flow.
The most definitive diagnostic tool is catheter-based angiography, also known as digital subtraction angiography (DSA). During this procedure, a thin tube (catheter) is guided to the artery of interest, and a contrast dye is injected to make the artery visible on X-ray images. This method provides a clear view of the artery’s structure and often reveals a classic “string of beads” pattern, where areas of narrowing alternate with areas of bulging, which is characteristic of the most common form of FMD.
Management and Treatment Approaches
Since there is no cure for fibromuscular dysplasia, treatment focuses on managing symptoms and reducing the risk of complications like an aneurysm or artery dissection. The management strategy is tailored to the individual, depending on the severity of their symptoms and which arteries are affected. Regular, long-term monitoring by a specialist experienced with FMD is a standard part of the care plan.
For many patients, the first line of treatment involves medication. To manage high blood pressure, doctors may prescribe medications such as ACE inhibitors or angiotensin II receptor blockers (ARBs). A daily low-dose aspirin might also be recommended to help prevent blood clots from forming in the narrowed sections of the arteries.
In cases where artery narrowing (stenosis) is severe and causing significant symptoms, a medical procedure may be necessary to restore adequate blood flow. The most common intervention is percutaneous transluminal angioplasty (PTA). In this minimally invasive procedure, a balloon-tipped catheter is inserted into the affected artery and inflated to widen the narrowed area. Unlike procedures for atherosclerosis, placing a stent is often not required for FMD-related stenosis.