More Research Is Needed to Understand and Treat Fibromuscular Dysplasia

Hello, and welcome to the April 2019 edition of Vascular Disease Management. I have chosen to comment on Dr Mehrdad Mac Farid and colleagues’ case report describing interventional therapy of a patient presenting with intermittent right thigh claudication secondary to fibromuscular dysplasia (FMD) of the external iliac artery. The patient had typical symptoms of intermittent claudication with a normal ankle-brachial index. Computed tomography angiography disclosed right external iliac fibromuscular dysplasia (FMD), which was confirmed by conventional angiography, and a pressure gradient was noted across the external iliac artery. Balloon angioplasty of the obstructive lesion failed to achieve an adequate vascular lumen; therefore, the external iliac artery was stented with a 7 mm self-expanding stent. After stenting, there was no significant residual stenosis and the translesion gradient was abolished.

I have chosen to comment on this case report as FMD was previously deemed to be an uncommon disease process, though recent reports have suggested that it is common. The most common vascular beds affected are the renal arteries and the extracranial carotid arteries, but the disease process can involve intracranial arteries, iliac arteries (most commonly the external iliac), subclavian and brachial arteries, vertebral arteries, and the mesenteric arteries. The presenting symptoms are related to the vascular bed that is affected. FMD typically causes symptoms secondary to obstruction, but it is strongly associated with spontaneous dissection and aneurysm formation. FMD is more common in females, with a 9:1 female preponderance.

The cause of FMD is unknown at this time. Evidence suggests that there may be a genetic basis for susceptibility to developing FMD.

FMD has been classified based on the layer of the artery that is affected. The most common type is medial FMD, which accounts for approximately 70% of all cases. Medial FMD is further divided into 4 types. The next most common type is intimal FMD, and the least common type is adventitial involvement. Each of the subtypes of FMD has a different angiographic appearance.

 The treatment of FMD includes medical therapy, interventional therapy, and surgery. Typically, medical therapy of renal artery FMD is preferred unless there is early hypertension, at which time renal artery percutaneous transluminal angioplasty (PTA) may result in a cure of the hypertension. When FMD involves other vascular beds, medical therapy includes the use of antiplatelet agents to prevent thrombosis and hypertensive therapy. Most commonly, obstructive FMD lesions that are not controlled by medical therapy are treated with progressive PTA until there is abolition of any gradient, but occasionally stenting is required if there is dissection or failure to abolish the translesional gradient, as demonstrated in this case report. Frequently, PTA results in a suboptimal angiographic appearance, but patency is high if gradients are abolished. Surgical therapies including bypass, renal artery re-implantation, and nephrectomy have historically been utilized.

 Although what we now term FMD was described as early as 1938 following nephrectomies for uncontrolled hypertension, FMD remains poorly understood. FMD appears more common than clinicians initially postulated and its reach is great, affecting multiple vascular beds with a wide variety of presentations. We have made no progress in preventing FMD, do not clearly understand its etiology, often mistake FMD for other disease processes, and are less than ideally successful in preventing its complications. We do know that when FMD is diagnosed that we should carefully examine other vascular beds for its presence.

 Clearly, more research is needed to better understand and treat this important disease process.