eMedicine Specialties > Neurology > Neuro-vascular Diseases

Fibromuscular Dysplasia

Author: James A Wilson, MD, MSc, FRCPC, BSc(H), Neurologist and Clinical Neurophysiologist, Oconee Neurology Services
Coauthor(s): Richard L Hughes, MD, Associate Professor, Department of Neurology, University of Colorado School of Medicine; Director, University of Colorado Affiliated Hospitals Stroke Project; Chief, Division of Neurology, Denver Health Medical Center
Contributor Information and Disclosures

Updated: Aug 30, 2007

Introduction

Background

Fibromuscular dysplasia (FMD) was first observed in 1938 by Leadbetter and Burkland in a 5-year-old boy, and described as a disease of the renal arteries. Involvement of the craniocervical arteries was recognized in 1946 by Palubinskas and Ripley.

FMD is an angiopathy that affects medium-sized arteries predominantly in young women of childbearing age. FMD most commonly affects the renal arteries and can cause refractory renovascular hypertension. Of patients with identified FMD, renal involvement occurs in 60-75%, cerebrovascular involvement occurs in 25-30%, visceral involvement occurs in 9%, and arteries of the limbs are affected in about 5%.^1,2 Case reports have shown FMD in most other medium-to-large arteries as well, including the coronary arteries³ , the pulmonary arteries⁴ , and the aorta⁵ . In 26% of patients, disease is found in more than one arterial region⁶ .

In patients with identified cephalic FMD, 95% have internal carotid artery involvement and 12-43% have vertebral artery involvement. Although FMD can affect arteries of any size⁷ , involvement of smaller ones, including intracranial vessels, is rare. Although an early autopsy series of 819 consecutive patients found the prevalence of FMD in the internal carotid arteries to be 1%⁸ , a larger, more recent autopsy series of 20,244 patients recently identified the overall prevalence of FMD of the internal carotid arteries to be only 0.02%⁹ . From a neurologic perspective, FMD is an important cause of stroke in young adults.

Pathophysiology

The etiology of FMD is not known, although the histopathologic findings have been described in detail (see Histologic Findings).

Although the etiology of FMD is unknown, several other associated vascular pathologies have been identified. In 1982, Mettinger and Ericson¹⁰ scrutinized 4000 consecutively performed cerebral angiographies and found 37 that were consistent with FMD. Of these, 19 patients had aneurysms. In 1988, Cloft et al performed a meta-analysis including 498 FMD patients as well as examined 117 of their own patients and found a combined prevalence of aneurysms to be 7.3%.¹¹

In 1975, Stanley et al found that 8 of their 17 cerebrovascular FMD cases had intracranial aneurysms, and they proposed a classification system that includes a "medial fibroplasias with aneurysms" subtype.¹² The beadlike dilatations observed within FMD lesions share gross and histologic characteristics of aneurysms. The casual link between FMD and aneurysms is less clear but is possibly related to an underlying connective tissue problem that results in loss of arterial wall strength. This wall weakness may allow for vessel dilation (aneurysm formation and beading in FMD) as well as injury, which then causes compensatory fibroplasia. Besides aneurysms, many case series and reports have identified FMD in patients presenting with arterial dissection.^13,14

FMD is a predisposing factor in 15% of spontaneous cervical carotid dissections (Saver, 1998). Dissections in FMD are more commonly multiple than in patients without an identified underlying arteriopathy.

FMD lesions likely predispose the artery to dissection through weakening of the arterial wall. Although the multiple manifestations of a structural arteriopathy in FMD hint of a genetic cause, such as collagen or elastin mutation, epidemiologic data suggesting familial transmission are generally weak.

The increased incidence of FMD in women as compared with men suggests a possible hormonal or genetic influence. Some authors have proposed the sex difference to be related to immune system functioning, but overt inflammation, as is observed in most classic autoimmune diseases, is histologically lacking.

Many reports exist of familial occurrences of FMD, mostly in siblings. Some studies have even suggested that familial occurrence is relatively common. For example, Rushton in 1980 suggested familial occurrences in relatives of 12 out of 20 identified probands.¹⁵ However, histologic proof was established in only the index cases, and vascular events such as early strokes and hypertension were used to identify the other affected family members. Most large series have reported that the great preponderance of FMD cases are sporadic. Bilateral renal FMD has been noted in a pair of identical twins.¹⁶

In case reports, FMD has been associated with mutations in collagen¹⁷ , with cutis laxa¹⁸ , and with alpha1-antitrypsin deficiency¹⁹ . Associative links to neurofibromatosis, Alport syndrome, and pheochromocytoma have also been suggested.²

Frequency

United States

Although early autopsy and radiologic series suggested that FMD involving the craniocervical arteries occurs at a frequency of approximately 1%, a more recent large series looking at FMD in the carotid arteries only suggests a lower frequency, on the order of 0.02%.⁹

International

The frequency is unknown.

Mortality/Morbidity

FMD generally follows a benign course and is frequently an incidental finding. However, cranial involvement bears worse prognosis because of the occurrence of dissection and strokes and the coexistence of saccular aneurysms. Specific mortality and morbidity data are lacking. 

Regarding the risk of recurrent carotid artery dissection, de Bray et al prospectively reviewed 103 consecutive patients with carotid artery dissection with follow-up for an average of 4 years. Of those, 5 had recurrent dissections and 4 of the 5 patients with recurrent dissections were diagnosed with FMD. If considering the presentation of recurrent dissection of the carotid artery, FMD was associated in 80% of their series.²⁰

Race

Whites are considered to be more commonly affected than blacks, although specific statistics on racial predilection are not available.

Sex

FMD occurs more frequently in women, at a ratio of approximately 3:1 to 4:1.

Age

FMD most commonly presents in young to middle-aged adults. One angiographic series found a mean age of 48 years with a range of 24-70 years.¹⁰ Cases have even been described in the pediatric population, including infantile-onset cases.²¹

Clinical

History

Most patients with craniocervical FMD are asymptomatic. Others report nonspecific problems such as headache, lightheadedness, vertigo, and tinnitus. Neck pain or carotidynia may be an initial presenting symptom due to arterial dissection. The symptoms of stroke can be varied but most often involve the anterior circulation because of the predilection of FMD to affect the extracranial carotid arteries.

Patients may provide a history of transient or permanent neurologic deficits of the face or extremities such as weakness or numbness, or they may experience visual changes or speech difficulties. No particular symptoms are pathognomonic for FMD, and any history compatible with a stroke in younger individuals may indicate underlying FMD. The family history should include information about relatives who have had vascular events at a young age.

One report notes an extremely unfortunate case of locked-in syndrome due to autopsy-proven basilar artery FMD.¹³ FMD may be complicated by stroke because of direct effects of craniocervical stenosis, dissection, or intracranial aneurysm, or the indirect effects of concomitant renovascular hypertension.

Symptoms compatible with a sentinel bleed, namely a sudden explosive headache followed later by neck stiffness, may signify the existence of an aneurysm, which in turn, may be associated with FMD.

A review of symptoms may provide clues of noncraniocervical FMD. Long-standing involvement of the renal arteries may lead to a history of hypertension. Rarely, abdominal pains, and even a history of ischemic bowel, may indicate mesenteric or visceral artery involvement. Vascular compromise of the limbs by FMD lesions may cause ischemic symptoms such as intermittent leg claudication.

Physical

Because of the broad possibilities of neurologic dysfunction due to stroke caused by FMD, a thorough neurologic examination should be performed. Findings may include anything from cranial nerve deficits to weakness, numbness, and coordination difficulties.

Sensitive signs of motor dysfunction such as pronator drift and plantar responses may yield deficits when formal power assessment does not. The neurovascular examination would not be complete without auscultation for carotid and vertebral artery bruits. If a headache history is provided, assessment for meningismus (eg, nuchal rigidity, Kernig sign, Brudzinski sign) may prove positive.

Because of the systemic nature of FMD, the general physical examination should include a search for signs of renal, visceral, and limb arterial involvement. These signs may include hypertension, decreased peripheral pulses, and even asymmetric limb pressures. Bruits may be found on auscultation of the renal, abdominal, iliac, or subclavian arteries.

Causes

The cause of FMD is unknown, despite some speculations related to its associations with some rare genetic conditions and predilection for young white females. Strokes can be caused by the FMD stenoses themselves, generally by thromboembolic events. Even without trauma, FMD lesions predispose the afflicted individual to arterial dissection, which in turn can cause embolic events or, rarely, local thrombosis and massive hemispheric stroke. Hypertension due to renovascular FMD may be a risk factor for lacunar and large vessel infarcts and even intracerebral hemorrhage.

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