Introduction 

Fibromuscular dysplasia (FMD) is a disease that affects your vascular system. The vascular system refers to the network of vessels, such as arteries and veins, that transports blood around your body. It is defined as non-atherosclerotic, meaning it is not associated with plaque build-up within your arteries, and as non-inflammatory, meaning it is not associated with swelling or inflamed blood vessels.

The disease is characterised by irregular cell growth within the artery walls. This consequently leads to an increased risk of stenosis (narrowing of a blood vessel), dissections (tear within the artery's inner wall), aneurysms (bulging due to a weak spot in an artery wall), and other complications. It most frequently affects the renal and carotid arteries, however, it can affect any artery, and most commonly affects those assigned female at birth (AFAB), typically presenting when you're in your thirties, forties, or fifties. It is a chronic, idiopathic (unknown cause) condition, yet patients typically have a life expectancy similar to the rest of the population. This article will explore the complications associated with FMD and how patients with it may reduce the risks linked to it.

Vascular complications of FMD

Unfortunately, FMD can significantly impact your vascular system and subsequent overall health. The associated complications of FMD can have serious implications for morbidity and mortality. 

Stenosis and hypertension 

The irregular growth of cells within the arterial wall can lead to stenosis, the most common symptom of FMD. This narrowing of the arteries restricts blood flow, causing hypertension (high blood pressure). This is most commonly seen in the renal arteries.

The renin-angiotensin-aldosterone system (RAAS) is a complex system involving hormones, proteins, enzymes, and biological reactions that regulate blood pressure and blood volume. As stenosis restricts blood flow, the RAAS attempts to accommodate by triggering an increase in systematic blood pressure. 

Studies have found that approximately 10% of renovascular hypertension cases are due to FMD, though this figure may vary depending on methodology, diagnostic approach, and the population studied.¹ 

Aneurysms

Most frequently occurring in the brain, visceral, and renal arteries, though they can occur anywhere in the vascular system, aneurysms also have the potential to be a grave complication of FMD. The abnormal bulging or dilation of the artery wall constitutes a serious risk of rupturing the blood vessel, resulting in severe, life-threatening haemorrhages. 

It, unfortunately, is a major risk for patients with FMD, studies have found approximately 23% of FMD patients have suffered at least a single aneurysm.^2,3 The threat posed can vary depending on the size of the aneurysm and where it is located. Intracranial (within the skull) aneurysms are notably concerning thanks to the risk of bleeding within the brain. 

Arterial dissections 

Arterial dissections refer to tears in the artery wall, allowing blood to flow between the layers of the artery and increasing the risk of rupture or occlusion (blockage) of the artery. Dissections are most likely to occur in the extracranial carotid, vertebral, renal, and coronary arteries and approximately 25% of FMD patients experience dissections.³

Cervical arteries, (arteries in the neck) are also often affected and can have neurological implications due to reduced blood flow to the brain. Dissections can also affect renal arteries, risking renal failure and hypertension. 

Stroke and transient ischemic attacks

Patients with a variant of FMD known as carotid web are at an increased risk of ischemic events such as stroke or transient ischemic attack (TIA). Both are conditions where blood flow is temporarily cut off from a part of your brain and FMD patients with carotid or vertebral artery involvement are particularly vulnerable. 

These ischemic events can happen as a result of stenosis, dissection, or aneurysms. Appropriate diagnosis and care require comprehensive imaging studies. Thankfully, there is evidence that the condition is amenable to stenting.^4,5

Spontaneous coronary artery dissection

Spontaneous coronary artery dissection (SCAD) is an uncommon but serious condition that predominantly affects those AFAB. It is characterised by a sudden tear in the coronary artery wall due to intramural bleeding, causing acute coronary syndrome (ACS). The rate of prevalence of FMD amongst SCAD patients has been reported as anywhere between 25% and 86%.⁶

The association between the two diseases is poorly understood, however, their potential link highlights the importance of considering FMD in young people AFAB who show signs of ACS, but without traditional cardiovascular risk factors. 

Risk mitigation strategies

There are multiple recommended risk mitigation strategies for patients with FMD, reflecting the variety and severity of FMD’s associated complications. 

Blood pressure management 

Managing blood pressure is essential in reducing the risk of aneurysm and dissection and can be particularly important in patients whose renal arteries are affected. Antihypertensive medications are routinely prescribed, in cases of renovascular hypertension, angiotensin-converting enzyme inhibitors (ACE inhibitors) or angiotensin II receptor blockers (ARBs) are recommended. If SCAD occurs, beta-blockers can have a protective effect.⁷

Revascularization procedures like angioplasty may be used in the management of severe hypertension or renal ischemia in some cases. 

Regular imaging and monitoring

There is variability in the location and manifestation of FMD, and such patients should undergo full head-to-pelvis imaging. Regular imaging is critical in tracking the progression of the disease and any complications like dissections and aneurysms. 

Non-invasive imaging such as computed tomography angiography (CTA), magnetic resonance angiography (MRA), and duplex ultrasonography are commonly used to both diagnose and subsequently monitor FMD.⁸ 

The exact choice of imaging can depend on the scenario and arteries involved. Periodic surveillance becomes even more important for patients with known aneurysms so that growth can be assessed and intervention implemented as required. 

Antiplatelet therapy

Thrombotic events (blood clots) may occur in patients with FMD as narrowing blood vessels may provide nexus points for clots to aggregate, as such antiplatelet therapy (blood thinning) is supported. It can be important for patients who are associated with cerebrovascular FMD or have a history of TIA or dissection. 

Aspirin is most commonly prescribed but it is important to be aware that there are no placebo-controlled studies for the use of antiplatelet therapy in treating FMD so its use should be carefully considered on a case-by-case basis.⁷

Lifestyle modifications

Lifestyle modifications can be crucial in managing FMD and mitigating the risk of serious complications. A particularly pertinent and recommended lifestyle change is for smokers to abstain. 

Smokers have an increased risk of developing FMD, and FMD patients with a history of smoking are significantly more likely to experience aneurysms. Smokers are also more likely to have major vascular events, such as TIA, brain haemorrhage, stroke, and major coronary events.⁸

Regular exercise, a healthy balanced diet, and maintaining a healthy weight can mitigate cardiovascular risk factors and are recommended. Managing stress may also be beneficial, as there is an association between stress and hypertension. 

Patient education and support

Education is vital, ensuring patients are aware of FMD, its symptoms, and potential complications is incredibly important. Patients should be aware of the signs and associated risks of dissection, stroke and ischemic events, SCAD, stenosis and hypertension, and aneurysm.

If you are ever concerned about the above conditions do not hesitate to consult a healthcare professional. The disease is chronic, which can have a negative psychological impact on patients. Counselling and support groups can provide mental and emotional help in such cases. 

Summary

Fibromuscular Dysplasia is a complex condition, the cause of which is poorly understood, that can manifest in a variety of ways and the complexity with which it affects the vascular system reflects that. It can result in potentially severe complications and most frequently affects those assigned female at birth. Thankfully, those with the condition typically have a similar life expectancy as the rest of the population. 

Stenosis and associated hypertension, aneurysm, dissection, stroke and transient ischemic attack, and spontaneous coronary artery dissection all have some degree of association with Fibromuscular dysplasia and require careful treatment and monitoring. The efficacy of management of the disease depends on a multidisciplinary approach, managing blood pressure, regular imaging and monitoring the progression of the disease, appropriate use of medications such as antiplatelet therapy, and appropriate lifestyle changes. 

Ongoing research is required to better understand the condition and to develop effective treatment and management options and diagnostic tools. As our understanding improves, so will the outcomes for patients.