What is the pathophysiology of fibromuscular dysplasia (FMD)?

Updated: Jul 27, 2018
  • Author: James A Wilson, MD, MSc, FRCPC; Chief Editor: Helmi L Lutsep, MD  more...
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Answer

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 Ericson [14] 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%. [15]

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. [11] 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. [16, 17]

FMD is a predisposing factor in 15% of spontaneous cervical carotid dissections. 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.


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