What is Fibromuscular Dysplasia (FMD)?

FMD is a non-atherosclerotic, non-inflammatory disease that predominately affects the renal and carotid arteries, although it has been described in all vascular beds. Approximately 60% to 75% of all FMD cases involve the renal rather then the carotid arteries. FMD more commonly affects women and younger individuals, though the sex distinction has not been proven in children. While its cause is not completely understood, hormonal, mechanical, and genetic factors are thought to play a role. Depending on the arterial layer that is affected, the disease may be characterized by multifocal, tubular, or focal stenosis, which is a narrowing of the arterial vessel caused by a deposition of collagen that protrudes into the lumen of the vessel. In addition to stenosis, vessels with FMD may develop weak points in the vessel wall that then become aneurysmal. The most prevalent form of FMD identified in children and young adults is intimal fibroplasia, which is typified by long, irregular or smooth, focal stenosis. Persons with FMD may be asymptomatic and only diagnosed at routine medical visits.

 Etiology

The etiology of FMD is currently unknown, although genetic, hormonal, and mechanical factors have been suggested. FMD may be more than a single condition with more than one cause.

 Clinical Presentations

Children often report various non-specific symptoms including headache, insomnia, fatigue and chest or abdominal pain, which may be indicative of hypertension, depending on which artery(s) is affected. A minority of children with hypertension present with neurological symptoms including seizures, transient ischemic attacks, cerebral infarctions, subarachnoid hemorrhages, and cranial nerve palsies.

 Classifications of FMD

 FMD lesions are classified according to the arterial layer they affect: intima, media, or adventitia. As stated previously, the most common form of FMD in children is intimal fibroplasia, which can occur in any arterial bed. Intimal fibroplasia may present as either a focal band-like narrowing, or a long, tubular narrowing.

 Diagnosis of FMD

FMD can be diagnosed by invasive and non-invasive means. Non-invasive testing includes duplex ultrasonography, magnetic resonance angiography (MRA), and computed tomographic angiography (CTA). The accepted gold standard is conventional angiography, however, by virtue of its invasive nature and risk involved its place in initial diagnosis is being challenged.

 Treatment of FMD in Children 

Both medical and surgical treatment options exist. Treatment involves controlling high blood pressure, re-establishing vascular flow, preventing clotting of the affected vessel(s), and eliminating factors that contribute to further vessel damage (e.g. smoking in teenagers). Use of a low estrogen dose birth-control pill in teenagers with controlled blood pressure should be weighed against a possible increased risk of vascular clotting. Medical therapy in children includes anti-hypertensive medications to control blood pressure. Aspirin should also be administered in children with FMD as anti-platelet therapy to reduce risk of thrombosis in affected vessels. Percutaneous transluminal renal angioplasty (PTRA) remains the treatment choice for renal-artery FMD. Indications for this intervention include recent or rapid onset of hypertension and difficulty in controlling high blood pressure with anti-hypertensive medications. Associated adverse events may include recurrent stenosis, arterial occlusion with renal loss, and arterial rupture and pseudo aneurysm formation. Due to the various medical therapies and percutaneous balloon angioplasty surgical reconstruction is reserved for patients with complex FMD.

 Prognosis

There are presently no specific studies or reports on the long-term prognosis and outcome of FMD in children. The causes, natural history, management and long-term outcomes of FMD in children require further research and evaluation.

 FMDSA Frequently Asked Questions were authored by Pam Mace RN, and Dr. Kevin Meyers M.D., Pediatric Nephrologist, Assistant Professor of Pediatrics, The Children's Hospital of Philadelphia and University of Pennsylvania

 

BIBLIOGRAPHY

Begelman, SM and Olin, JW.  Fibromuscular Dysplasia,  Current Opinion in Rheumatology.  (2000) 12:41-47.

Fenves, AZ and Ram, CV.  Fibromuscular Dysplasia of the Renal Arteries, Current Hypertension Reports.  (1999) 1:546-549. 

Lusher, TF, Keller HM, Imhof, HG, Griminger, P, Kuhlmann, U, Largiader, F, Schneider, E, Schneider, J, Vetter, W.  Fibromuscular Hyperplasia: Extension of the disease and therapeutic outcome.  Results of the University Hospital Zurich Cooperative Study on Fibromuscular Hyperplasia.   Nephron.  (1986).  44(Suppl 1): 109-114. 

Lusher, TF, Lie, JT, Stanson, AW. Houser, OW, Hollier, LH, and Sheps, SG.    Arterial Fibromuscular Dysplasia, Mayo Clinic Proceedings.  (1987) 62: 931-952.