Fibromuscular dysplasia (FMD) has been defined as a non-atherosclerotic, non-inflammatory vascular disease that can result in arterial stenosis, occlusions, aneurysms, or dissections. Although the cause of FMD and its prevalence in the general population are unknown, research has shown that it has been reported in virtually every arterial bed. Most commonly, FMD affects the renal and extracranial carotid and vertebral arteries. When the renal artery is involved, the most frequent finding is hypertension. Carotid or vertebral artery FMD may lead to dizziness, pulsatile tinnitus, transient ischemic attack (TIA), or stroke.
According to Jeffrey W. Olin, DO, FACC, FAHA, there is an average delay of 4 to 9 years from the time of the first symptom or sign to a diagnosis of FMD. “Many consider this disease rare, but in reality, the diagnosis is often overlooked,” he says. “Thus, it’s not considered in a differential diagnosis. In addition, FMD is poorly understood by many healthcare providers. Many of the signs and symptoms are non-specific, which in turn can lead clinicians down the wrong diagnostic pathway.” He notes that a delayed diagnosis can impair quality of life and result in poor outcomes.
In 2014, the American Heart Association (AHA) released a scientific statement on FMD that addressed the state of the science and critical unanswered questions. “Over the last several years, we have learned that FMD is more common than previously thought,” says Dr. Olin, who chaired the AHA writing committee that developed the scientific statement. “FMD is frequently being discovered incidentally while imaging is performed for other reasons in asymptomatic patients without classic risk factors for atherosclerosis. The clinical manifestations of FMD vary from patient to patient. However, it is important to recognize that one of every three patients will have an aneurysm and/or dissection. Therefore, it is recommended that every patient undergo a CT angiogram or magnetic resonance (MR) angiogram from head to pelvis to exclude the presence of aneurysm and dissection.”
Diagnosing Fibromuscular Dysplasi
The AHA scientific statement outlines several diagnostic strategies for FMD that clinicians are encouraged to use. “FMD is classified as multifocal or focal,” explains Dr. Olin (Table 1). “Classifying FMD appropriately is important in determining how patients should be treated.” Imaging has become the primary method for diagnosing FMD. Non-invasive imaging studies, such as duplex ultrasound, CT angiography, and MR angiography, can be of benefit, but the gold standard is catheter-based angiography. Studies comparing the diagnostic accuracy of non-invasive imaging have involved mostly patients with atherosclerotic renal artery and carotid artery disease. Little information is available that specifically addresses the accuracy of non-invasive imaging for FMD.
Treating Fibromuscular Dysplasi
Advances in imaging, medical, and endovascular therapies have made treatment of patients with FMD less invasive, safer, and more effective, according to Dr. Olin. Treatments may include:
♦ Medical therapy and surveillance.
♦ Endovascular therapy for stenosis (angioplasty), dissection (stents), or aneurysms (coils, stents).
“The therapeutic decision will depend on the nature and location of vascular lesions, the presence and severity of symptoms, and prior vascular events relating to FMD,” Dr. Olin says. “Treatment decisions will also depend on the presence and size of aneurysms and comorbid conditions.” The AHA scientific statement notes that most treatment decisions in patients with FMD are based on data coming from single-case reports or small retro-spective case series.
According to the AHA, revascularization by percutaneous transluminal angioplasty should be considered in patients with renal artery FMD who have the appropriate clinical presentation. Younger patients with a shorter duration of hypertension have a greater likelihood of a cure for hypertension. “Renal artery stenting is rarely needed to treat stenosis,” adds Dr. Olin, “but if a dissection is present, stenting is generally the procedure of choice.” Surgical resection, endovascular coiling, or covered stents are treatment options usually used for renal artery aneurysms.
Several commonly held misconceptions concerning FMD continue to present themselves in published literature, according to Dr. Olin (Table 2). “These misconceptions highlight the need for additional research into the pathogenesis, diagnostic approaches, natural history, and outcomes of FMD,” he says. To date, there have been no randomized controlled trials of medical therapies or endovascular treatments for FMD. The AHA writing committee identified research priorities in the field of FMD that it hopes will serve as an impetus for additional research.
Given the uncommon nature of FMD, Dr. Olin says that funding for research is challenging. “The research we have has been driven largely by patients who are diagnosed with FMD and seek information on it,” he says. “To significantly advance our understanding of FMD, we need collaboration across a large network of research and clinical centers in the United States and abroad.”
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