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Fibromuscular Dysplasia in Clinical Practice:A Case-based Review
  JOHTN
SECONDARY HYPERTENSION
Fibromuscular Dysplasia in Clinical Practice:
A Case-based Review
1K Jitender Reddy, 2K Pradyumna Reddy
1Assistant Professor, Senior Consultant and Head, 2SeniorRegistrar
1Department of Radiology, AIMSR, Apollo Hospitals, JubileeHills; Apollo Hospitals and Apollo Medical College, HyderabadTelangana, India
2Department of Radiology, Apollo Hospitals and Apollo MedicalCollege, Hyderabad, Telangana, India
Corresponding Author: K Jitender Reddy, Assistant ProfessorSenior Consultant and Head, Department of Radiology, AIMSRApollo Hospitals, Jubilee Hills; Apollo Hospitals and Apollo MedicalCollege, Hyderabad, Telangana, India
e-mail: kjitenderreddymdrd@gmail.com
 
ABSTRACT
Fibromuscular dysplasia (FMD) is an idiopathic, nonatherosclerotic,noninflammatory disease with segmental involvementof the blood vessels that cause abnormal growth within thewall of an artery in any region of body. Fibromuscular dysplasiahas been found in nearly every arterial bed in the body.However, the most common arteries affected are the renaland carotid arteries. It is a heterogeneous group of vascularlesions characterized by an idiopathic, noninflammatory, andnonatherosclerotic angiopathy of small and medium-sizedarteries. The prevalence of FMD is estimated between 4 and6% in the renal arteries and between 0.3 and 3% in the cervicoencephalicarteries.
Imaging and radiologists play an important role in diagnosingthe abnormality with knowledge of patient complaints with respectto fibromuscular disease. The most common imaging finding isdilatations, beaded appearance of vessels, and aneurysms. Theless common findings are tortuous vessels, ectasia, kinking,loops, and dissection. The radiologist should be aware of theseso that FMD can be diagnosed in young females with hypertensionnot responding well to treatment or familial hypertension.
Its signs and symptoms help the radiologist to diagnoseearly. The objective of this review is therefore to increaseradiologists' and clinicians' awareness of FMD's epidemiology,pathophysiology, clinical presentation, classical and minor/rare radiological findings, and possible complications in otherarteries in the abdomen.
Epidemiology: The prevalence is unknown. It is most commonin young women with a female to male ratio of 3:1, and is typicallydiagnosed between the ages of 30 and 50 years. It is lessthan 2% of all hypertensions.
Keywords: Computed tomography angiography, Digital subtractionangiography, Fibromuscular dysplasia, Hypertension,Magnetic resonance angiography, Percutaneous transluminalangioplasty, Renal arteries, Renal artery stenosis.
How to cite this article: Reddy KJ, Reddy KP. FibromuscularDysplasia in Clinical Practice: A Case-based Review. HypertensJ 2017;3(2):101-104.
Source of support: Nil
Conflict of interest: None
 
 

 
CASE REPORT

Mrs. KVR, a 37-year-old woman, was seen in the bloodpressure clinic of Apollo Hospital, Hyderabad, becauseof new-onset uncontrolled hypertension. Her familyphysician noted that the patient's blood pressure levelwas consistently above 200/120 mm Hg despite fourantihypertensive drugs on optimal doses. Her bloodurea nitrogen/creatinine/sodium/potassium levels, chestX-ray, and electrocardiogram were all normal.

Based on her history of new-onset progressive hypertension,workup was done for secondary causes. Computedtomography angiography (CTA) of renal arteriesrevealed bilateral significant fibromuscular dysplasia(FMD; Figs 1 and 2). As the blood pressure levels remainedabove 200/120 on medical treatment, she underwent bilateralrenal artery angioplasty (with stent placement on oneside); following successful renal angioplasty, her bloodpressure started decreasing and became normal requiringdiscontinuation of antihypertensive drug therapy. At3- to 4-month follow-up, her blood pressure was 132/84mm Hg on no antihypertensive drugs. The clinical andblood pressure course indicated that her hypertensionwas cured. This case is a classical illustration of secondaryhypertension due to FMD of renal arteries and promptresolution of hypertension after successful angioplasty.

Fibromuscular Dysplasia in Clinical Practice:A Case-based Review
Fig. 1: Reconstructed CTA view bilateral FMD

 
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Fibromuscular Dysplasia in Clinical Practice:A Case-based Review
Fig. 2: Left renal artery after successful angioplastyof FMD lesions

INTRODUCTION

Fibromuscular dysplasia is a systemic vascular diseasewhich predominantly affects small- and medium-sizedarteries. Although this arterial anomaly can affect anyartery, its hemodynamic and clinical relevance is limitedto renal arteries. The FMD affecting the renal arteries isan important cause of "secondary" hypertension. Thereis ample evidence to suggest that mechanical correctionof renal FMD improves or cures hypertension. The FMDis a nonatherosclerotic entity that occurs predominantlyin females and in the younger individuals. Perhaps, renalartery involvement by FMD is more common than othervascular beds (visceral, craniocervical, or in the limbs).The exact prevalence of FMD is probably not knownsince every patient with hypertension is not subjected toworkup and since arterial biopsies are rarely obtained.The most frequent manifestation of FMD is systemichypertension due to renal artery involvement. The FMDis more common in women between the ages of 30 and50 years. Women are 10 times more likely to have FMDthan men.

Pathological Lesions in FMD

Typical FMD is idiopathic in nature, segmental, noninflammatory,and nonatherosclerotic, resulting in stenosis(of small- and medium-sized arteries). Three varieties ofFMD have been described based on which layer of theartery is the culprit-intimal, medial, and perimedial.By far, the most common pathological type is medialFMD. Angiographically, medial FMD has the "string-ofbeads"appearance. It has a classic image on angiography.Alternating regions of "thinned" media and "thickened"fibromuscular collagen are responsible for the "stringof-beads" appearance of medial FMD, usually involvingthe distal two-thirds of the main renal artery. While FMD is a nonatherosclerotic disease, it can coexist withatherosclerosis.
 
Intimal FMD occurs in less than 10% of all the lesions.Eccentric deposition of collagen and other fibrinous materialson the intima is based on the anatomy of the disease.At times, the angiographic features may mimic those ofendarteritis. Intimal FMD may be highly focal and concentric,which may be mistaken for an atherosclerotic lesion.

Perimedial fibrodysplasia occurs in about 15% of theindividuals afflicted with FMD. This pathological entitymay cause severe stenosis.

Adventitical fibrodysplasia is very rare (less than 1%).Dense collagen deposition occurs in the adventia. Theother layers of the artery are intact.

Pathogenesis

The precise etiology of FMD is unknown. Geneticsmay play a role due to high incidence of FMD incertain families. Although the exact genetic mutationor transmission is unknown, genetics may play a rolein the inheritance of FMD. Hormonal factors are likelyimportant as FMD occurs overwhelmingly amongwomen. There may be a genetic susceptibility to FMD.Since FMD is not a common entity, large cohort studiesare not available. The phenotypes in FMD are variableand may be confined to some subsets but not proven.Family-based studies with complementary geneticapproaches are needed to identify genetic pathways forFMD. There are reports that cigarette smoking may bea risk factor for FMD.

Renal FMD and Hypertension

Atherosclerotic lesions of the renal artery are morecommon than FMD. However, correction of FMDimproves or cures hypertension unlike atheroscleroticrenal artery stenosis (RAS). Therefore, in the workupfor secondary forms of hypertension, FMD should beconsidered especially in the young and in females. Anydegree of hypertension in young women warrants considerationof FMD of renal arteries. It is a potentiallyreversible disorder and hence, should not be missed inthe clinical setting. Usually, FMD (especially, the medialfibrodysplasia) is a stable condition and does not causeischemic nephropathy. However, it can cause severe,progressive, and resistant hypertension. Thus, FMD ofrenal arteries should not be overlooked in suspectedpatients. The FMD typifies classical "renovascular"hypertension, which is mediated by the activationof renin-angiotensin system. Ischemia to the kidneycaused by significant RAS stimulates renin release culminatingin the generation of angiotensin-II, a powerfulvasoconstrictor.
 
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Fibromuscular Dysplasia in Clinical Practice

Clinical Suspicion

In young patients (especially, female) with any degreeor duration of confirmed hypertension, workup forFMD-RAS is indicated.
  • Age < 35 years, especially women
  • Confirmed hypertension
  • Accidental discovery of unilateral small kidney
  • Abdominal bruit
  • Known FMD in any vascular bed

Diagnostic Evaluation of FMD

Standard (conventional) renal arteriogram is the mostdefinitive test (gold standard) to diagnose RAS due toFMD. However, certain less precise noninvasive testsmay offer clues to the presence of RAS.

Duplex Ultrasound

Duplex ultrasound is much less sensitive than CTA ormagnetic resonance angiography (MRA) for detectingRAS. However, it is less expensive and readily availablefor the initial screening purpose. The procedure,however, is highly operator dependent and requires thecooperation of the patient to hold their breath during theprocedure. Duplex ultrasound may reveal RAS and alsoprovide information about the kidney size. It is a reasonablefirst-line screening test but not conclusive and shouldbe followed by CTA or MRA. Duplex ultrasound mayshow arterial stenosis, increase in peak systolic velocity,and a delayed systolic upstroke distal to the lesion. Bloodvessel tortuosity and turbulence can be identified on colorDoppler. While the duplex ultrasound may only serve asa screening test for RAS, it is a reliable technique to followup the patients after angioplasty.

Computed Tomography Angiography and
Magnetic Resonance Angiography


Both CTA and MRA provide acceptable sensitivity andspecificity in detecting RAS from any cause includingFMD. The CTA probably is slightly superior to MRA inproviding the anatomy of renal arteries and the kidneys.The CTA offers superior spatial resolution compared withMRA. Also, distal renal artery is better visible with CTAcompared with MRA. Calcifications can also be visualizedwith CTA. But irradiation and contrast-mediatedrenal injury are disadvantages of CTA.

The MRA may at times overestimate the degree ofRAS. And spatial resolution is not optimal comparedwith CTA. The MRA is preferable for patients who mayotherwise be at risk for contrast nephrotoxicity. The choicebetween CTA and MRA depends on the expertise availableat the facility and experiment.

 
Renal scintigraphy and digital subtraction angiographyhave no convincing role in the diagnosis of RASgiven the usefulness of CTA and MRA.

MANAGEMENT Of FMD

Once the diagnosis of RAS due to FMD is confirmedbased on clinical assessment and a definitive procedure(CTA or MRA), appropriate management strategy shouldbe planned to correct the lesion and to improve or curehypertension. There are no randomized controlledstudies comparing surgical revascularization of RAS(from FMD) with percutaneous transluminal angioplasty(PTA). However, the most preferred therapeutic choiceto correct FMD is clearly PTA. At present, the need forsurgical correction of FMD is not recommended giventhe success of PTA in treating this condition. Currently,PTA without stenting is the treatment of choice forpatients with renovascular hypertension with FMD as theetiology. Primary PTA of the FMD lesions (unilateral orbilateral) should suffice; stenting is only indicated if thereis significant periprocedural dissection or if angioplastydoes not produce optimal relief of the stenosis.

In patients with RAS due to FMD, PTA of the lesions(unilateral or bilateral) results in a remarkable improvement(or cure) of hypertension provided the procedureis a technical success. In nearly 90% of patients, PTAresults in a dramatic fall in blood pressure. Nearly a thirdof patients with FMD have involvement of branch renalartery that may pose technical challenges for performingPTA but can be attempted. For patients who are unableor unwilling to undergo PTA, hypertension should betreated medically. The treatment regimen should includeblockers of the renin-angiotensin-aldosterone system.The goal is to control hypertension effectively.

There are no specific guidelines on how to followup the patients with FMD who have undergone PTA.Perhaps, the first follow-up visit should be within the firstmonth after PTA and 6 to 12 months thereafter based onthe clinical assessment and blood pressure levels.

CONCLUSION

The RAS due to FMD is potentially a curable form ofsecondary hypertension. Clinical suspicion should leadto diagnostic workup followed by management strategy(usually PTA). Future research should identify geneticand environmental factors in the pathogenesis of FMD.It is also important to identify in the clinic those hypertensivepatients who may have underlying FMD as theetiology. Certainly, FMD represents a truly correctiblecause of hypertension in the community. Therefore, itis an important clinical entity because safe therapeuticoptions are available with superb clinical outcomes.

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