Overview

The term fibromuscular dysplasia (FMD) is probably something you haven’t heard before, but it is a rare condition of the arteries which mostly affects person assigned female at birth (AFAB). FMD is mostly silent, until it is not, resulting in strokes and aneurysms, making this a highly dangerous disease.

Despite the disease being rare, it may be more common than we think, due to its lack of symptoms. Although FMD cannot be cured, it can be treated and managed to enable individuals suffering from this disease to live a high-quality life. This article hopes to raise awareness for FMD, with particular emphasis on how it can be monitored and treated.

What is fibromuscular dysplasia?

Fibromuscular dysplasia, or FMD, is commonly referred to as a rare noninflammatory, nonatherosclerotic vascular disease which is characterised by abnormal growth of cells in arterial walls, leading to stenosis (narrowing of the arteries).⁶ This abnormal growth can cause a range of complications, including dissections, strokes, and aneurysms of the arteries.⁴ The disease is found to be much more prevalent among individuals AFAB, particularly those between the ages of 20-60, who account for 80-90% of those affected by the disease.^1,2

Although FMD can affect any artery within the body, it commonly affects either the renal or cerebrovascular arteries (including the carotid and vertebral arteries).^2,3 In fact, it has been seen that around 80% of patients have renal FMD, whilst 75% have cerebrovascular FMD .³ However, patients can also have a combination of both renal and cerebrovascular, or other less common arterial FMD.

How common is fibromuscular dysplasia?

FMD is traditionally considered a relatively rare disease, but its prevalence may be significantly higher than previously estimated. A kidney donor screening study revealed that FMD could affect up to 4% of adults.³ In a study by Neymark et al., 6.6% of individuals who were candidates for renal donation showed evidence of fibromuscular dysplasia. This suggests that approximately 5.8 to 8.6 million people in the United States may potentially have this supposedly rare condition.¹

However, the actual numbers could be even higher, as FMD often goes undiagnosed. This is partly due to a lack of awareness among medical professionals and the fact that many individuals with FMD are asymptomatic.

What causes fibromuscular dysplasia?

The exact cause of FMD is unknown and is typically classified as idiopathic, however, several factors have been proposed:

• Genetic factors: A genetic role has been suggested due to an autosomal dominant pattern being seen to be inherited within families, however, this evidence is limited² 
• Environmental factors: Smoking has been associated with an increased risk of aneurysms in FMD individuals, however, studies have found that a majority of individuals AFAB with FMD have never smoked⁵
• Hormonal factors: Given a higher prevalence of FMD in individuals AFAB, hormonal factors such as birth control have been considered, however, there is little to no evidence to support any of these concerns²
• Transforming growth factors (TGF): Emerging research is investigating the correlation of elevated TGF in patients with FMD⁵

Diagnosis of fibromuscular dysplasia

Diagnosis of FMD is often delayed leading to prolonged periods of poorly controlled hypertension, strokes, aneurysms, and dissection of arteries, which lowers the quality of life for patients with FMD.⁵ Therefore, improving and increasing diagnosis is vital to allow for proper management and treatment of the disease. FMD can be identified through angiography and classified into 3 categories:

• Intimal fibroplasia 
• Medial dysplasia (most common with around 80-90% of FMD being this type) 
• Adventitial fibroplasia^1,5

Clinical presentation

• Hypertension: especially in renal artery FMD¹
• History of vascular events:
  • Aneurysms of the artery
  • Dissection of artery
  • Occlusion of artery
• Symptoms: such as headaches and pulsatile tinnitus in cerebrovascular FMD²

Imagery diagnosis

• Catheter-based angiography: Used to look at the renal artery and measure pressure gradient^1,2
• Duplex ultrasound: To screen renal artery and carotid artery, where it can be used to differentiate from atherosclerosis^3,5
• String of beads appearance: This is a characteristic imaging feature of FMD, showing bead-like dilations along the affected arteries⁵
• Microaneurysms: These can be identified through imaging and are significant because they carry a high risk of rupture in FMD patients⁵

Treatment and management of fibromuscular dysplasia

While there is no cure for FMD, it can, however, be managed through careful monitoring and treatment of the symptoms.⁴ Unfortunately, because it is a rare disease, medical professionals are often limited with non-standardised treatment options, as well as a lack of evidence to support these treatments. Treatment and management of FMD require highly comprehensive imaging techniques that are non-invasive to identify suitable medical treatments for the patient and decide whether vascular interventions are required.⁴

Monitoring and treatment of renal FMD 

Renal FMD is commonly associated with hypertension, which is often asymptomatic. Patients with renal FMD are advised to undergo monitoring of blood pressure every 6 months.¹ Additionally, they should undergo an assessment of blood for electrolytes and overall renal functioning, including a urinalysis for albuminuria.²

Initial treatment

• Balloon angioplasty: This is the preferred initial treatment due to its high success rate, short recovery time, and minimally invasive nature
• Surgical revascularisation: Although an option, it is less commonly performed compared to angioplasty¹

Post-treatment monitoring

• Ultrasound surveillance: Following angioplasty, ultrasound monitoring of the kidneys is recommended for 6 to 24 months to detect potential restenosis
• Blood pressure monitoring: Continuous monitoring of blood pressure is essential. If hypertension persists after the initial procedure, repeat angioplasty or surgical intervention may be necessary^1,2

For the management of renal FMD, antihypertensive medications such as angiotensin-converting enzyme inhibitors or angiotensin II receptor blockers can be prescribed. Aspirin is also commonly prescribed.¹

Monitoring and treatment of cerebrovascular FMD

Patients with cerebrovascular FMD are advised to have imaging every 6-12 months to assess how medical professionals should continue with treatment and management of symptoms.¹ Medical professionals should pay careful attention to arterial dissections, as these can lead to strokes.

Dissections of the vertebral or carotid artery can be promptly treated by the administration of anticoagulants, such as heparin and warfarin.¹ Anticoagulants are advised to be continued for 3-6 months by the American Heart Association/American Stroke Association guidelines.²

If a stroke occurs a balloon percutaneous transluminal angioplasty (PTA) can be carried out.¹ Alternatively, stents and coils can be surgically placed to open blood vessels if there is a stroke or aneurysm.¹ 

For individuals suffering from acute strokes, thrombolysis treatments have been suggested, however, there is little evidence for the success of these treatments.²

Symptoms management of cerebrovascular FMD

• Ear whooshing or pulsatile tinnitus: Persistent sounds are seen in 32% of patients with FMD according to the US registry.² These symptoms require discussion with an audiologist to manage these symptoms³
• Headaches: Seen in 67.5% of patients according to the US registry.² A recent study on 4 patients with carotid artery FMD who had chronic headaches found relief after a balloon angioplasty¹

Pregnancy

Since FMD predominantly affects individuals AFAB, particularly those of child-bearing age, pregnancy management is crucial. Individuals AFAB with FMD are at a higher risk of complications such as preeclampsia. Regular monitoring by healthcare providers is therefore essential for the health of the patient.² Referral to a high-risk obstetrician is recommended to develop a comprehensive treatment plan, taking into account any prior history of aneurysms, strokes, or arterial dissections.⁵

Education

Patients diagnosed with FMD should be educated on making healthy lifestyle choices, such as not smoking to prevent further increasing their risk of aneurysms.⁷ Furthermore, patients should be made aware of what can increase their risk factors for a stroke and how they can prevent arterial dissections. For example, they should avoid participating in activities or sports that may cause neck injuries.⁷

Summary

Fibromuscular dysplasia (FMD) requires extensive longitudinal care and management due to it being a chronic vascular disease. Although it is possible to manage renal and cerebrovascular FMD, treatment and management options for other forms of FMD are less well understood. Currently, the management of FMD is highly unstandardised, with limited research and few publications, most of which are single case reports. Increasing awareness, improving imaging techniques for diagnosis and monitoring, and standardising treatment options could significantly enhance the quality of life for individuals living with FMD.