Fibromuscular dysplasia overview

# Overview
The definition of Fibromuscular Dysplasia(FMD) on the Medical Subject Headings is "an idiopathic, segmental, nonatheromatous disease of the musculature of arterial walls, leading to stenosis of small and medium-sized arteries. There is a true proliferation of smooth muscle cells and fibrous tissue formation. however, this systemic arteriopathy is a noninflammatory process and is therefore not associated with inflammatory biomarkers.
According to the definition, FMD is a condition which can involve every vascular bed in the body, therefore it can cause very heterogeneous and extensive spectrum of clinical manifestations from asymptomatic involvement to devastating consequences and morbidity and mortality.
Unlike routine conception that FMD is a rare disease of middle-aged female, current data from the French and US registries showed that the awareness about FMD must be raised, and every health provider at any level should be familiar with suggestive symptoms and signs of FMD which is more frequent and more often systematic than previously thought.

# Historical Perspective
Fibromuscular dysplasia was first discovered by Leadbetter and Burkland, in 1938 following evaluation of severe hypertension in a 5-year-old boy. The first histopathological description of fibromuscular dysplasia and pathologic classification for this condition was proposed in 1958 and 1971 by McCormack and coworkers, respectively. 
Fibromuscular dysplasia with involvement of extrarenal arteries has been considering in recent years. However numerous aspects of molecular biology and genetic etiology of this condition remain unanswered, and there are various top research priorities in the field of FMD to improve our understanding of this condition.

# Classification
The classification system for fibromuscular dysplasia (FMD) was first according to the arterial layer involved. (tunica intima, tunica media , or adventitia) . However, with use of transluminal percutaneous angioplasty (TPA) for treatment of FMD lesions and its preference rather than surgery, the obtaining of pathological specimens are restricted. Thus, today, FMD is a disease diagnosed radiographically and histopathological classification has been replaced by the arteriographic findings.

# Pathophysiology
In Fibromuscular dysplasia, the proliferation of vascular smooth muscle of one or more small or medium-sized arteriesundergo dysplasia and cause stenosis. this abnormal cellular development is characterized by fibrous thickening of the intima, media, or adventitia of the involved arteries; which ultimately lead to arterial narrowing.

# Causes
The cause of fibromuscular dysplasia has not been identified. To review risk factors for the development of FMD, click here.

# Differentiating Xyz from Other Diseases
Fibromuscular dysplasia must be differentiated from other diseases that present clinical features of multisystem involvement, hypertension, aneurysm, and dissection, such as atherosclerotic vascular disease, vasculitis, and Ehlers-Danlos Type IV.
There is a significant delay in diagnosis from the first onset of clinical symptoms/signs of 4.4 years in men and 4.1 years in women. There are several possible reasons for such a delay, including the possibility that FMD is not considered in the differential diagnosis of a patients symptoms because of under-recognition of this disorder, the mistaken belief that FMD is predominately a rare disease of young patients, and the fact that many of the signs and symptoms of FMD are nonspecific, such as dizziness, tinnitus, and headaches.

# Epidemiology and Demographics
The prevalence of FMD in the general population is not known. In some studies, the prevalence of renal artery FMD has been calculated to be approximately 4 per 100 adults.

# Risk Factors
There are no established risk factors for fibromuscular dysplasia; nevertheless, there are some evidences that cigarette smoking, hypertension and other classic risk factors for atherosclerosis may be risk factors in the development of FMD.  FMD has a greater prevalence among women but no definite association has been found between this condition and use of oral contraceptives or disturbances of endogenous sex hormones. Since the disease is more common among the first-degree relatives of patients with FMD, Genetic factors may play a role in the development of FMD. 

# Screening
According to the American Heart Association (AHA)/American College of Cardiology guidelines, and European consensus on the diagnosis and management of fibromuscular dysplasia, there are some recommendations and indications for the screening of FMD-related RAS, cervicocephalic FMD, and in first-degree relatives of patients with FMD.

# Natural History, Complications, and Prognosis
Current knowledge about natural history, the efficacy of medical therapies, complications, and prognosis of FMD, are really restricted; however the natural history of FMD is benign, and the long-term prognosis of patients with FMD is good, and its existence alone is not an indication for preventive intervention or surgery.
Renal or cervival artery dissection and Intracranial aneurysms rupture and SAH are the most common complications of FMD.

# Diagnosis

## Diagnostic Study of Choice
Catheter-based angiography is the gold standard test for the diagnosis of renovascular fibromuscular dysplasia. Imaging modalities are the methods for diagnosing FMD. Duplex ultrasonography, accompanied by computed tomographic angiography(CTA), and magnetic resonance angiography (MRA), are imaging techniques for detecting FMD lesions but the gold standard remains catheter-based angiography.

## History and Symptoms
Since Fibromuscular dysplasia can involve virtually every artery of the body, thus the clinical presentations of FMD vary widely and are determined by the vessels territories that are involved.The clinical presentations of FMD may result from the stenosis, occlusion, ischemia, dissection, rupture of aneurysms and embolization of intravascular thrombi from dissection or aneurysms.

## Physical Examination
Patients with FMD usually appear normal. In physical examination of patients with FMD mild to moderate hypertension may be detected. In the auscultation of neck among patients with involvement of carotid artery or auscultation of epigastric or flank of renovascular FMD bruits may be heard. Eventullay due to nonspecific sypmtoms and sings of FMD, the diagnosis of this disease needs highly clinical suspicion of healthcare provider.

## Laboratory Findings
There are no diagnostic laboratory findings associated with fibromuscular dysplasia.

## Electrocardiogram
There are no ECG findings associated with FMD.

## Ultrasound
However, duplex (doppler with B-mode) ultrasound is less sensitive than CT-angiography and MRA for detecting atherosclerotic RAS and FMD-related RAS, but convenient availability, modest expenditure, non-irradiating and easily providing information about kidney size, the hemodynamic impact of the stenosis, and associated renal disease, makes DUS as a reasonable first-line screening imaging modality.

## CTA
Computed tomography angiography (CTA) has really excellent diagnostic exactness for FMD of the renal arteries. CTA may use in the diagnosis of FMD of the cervicocephalic arteries and to find associated intracranial lesions.

## MRA
Magnetic resonance angiography (MRA) in comparison with DUS and CTA is less preferred. In MRA images there is an inadequate spatial resolution in the branch vessels, as well as pseudo-beading features from artifact impact. However, MRA can be useful for detecting aneurysms and dissections.

## Arteriography
Arteriography remains the gold standard in diagnosis of FMD. Angiography with contrast will show a characteristic "string of beads" morphology in a vessel affected by FMD.

# Treatment

## Medical Therapy
Pharmacologic medical therapies for treatment of renovascular hypertension in FMD patients include ACE inhibitors and angiotensin receptor blockers (ARBs).If a second medication is needed, the addition of a thiazide diuretic is an acceptable choice. Among patients with an ischemic event, antiplatelet therapy is generally used

## Surgery
Revascularization by surgical intervention or percutaneous transluminal angioplasty (PTA) , are  not the first-line treatment options for patients with FMD, however in cases of FMD-related RAS with  signs of downstream reduction of renal function or in case of drug-resistant HTN vascular reconstruction should be considered.

## Primary Prevention
There are no established measures for the primary prevention of fibromuscular dysplasia.

## Secondary Prevention
There are no established measures for the secondary prevention of FMD.