What is fibromuscular dysplasia?

Fibromuscular dysplasia (FMD) is a rare disorder of the arteries,⁴ marked by the narrowing and abnormal thickening⁴ of the arterial walls, resulting in its characteristic ‘beaded appearance’.³

Fibromuscular dysplasia predominantly affects small and medium-sized arteries and is most commonly observed in the renal arteries (supply blood to the kidneys) and the carotid arteries (supply blood to the brain).⁸ However, it can also occur in other arteries, such as the mesenteric arteries ( supply blood to the intestines).⁹

FMD can lead to serious complications, such as aneurysms (artery bulges)¹¹ and dissections (tears in the arterial walls).⁴ 

What are the symptoms and characteristics of fibromuscular dysplasia?

The symptoms and characteristics of fibromuscular dysplasia (FMD) vary from patient to patient, depending on the artery or arteries affected. 

When the renal artery is affected, the patient may present with:^2,4

• High blood pressure 
• Renal artery aneurysm or dissection
• Impaired kidney function

When the carotid artery is affected, the patient may present with:^2,4

• Headaches, particularly migraine-like
• Ringing or whooshing sound in the ears (tinnitus)
• Neck pain
• Carotid bruit⁹
• Dizziness
• Brain aneurysm
• Transient ischaemic attack (TIA) or stroke

Patients with FMD can also remain asymptomatic, which is why most cases are diagnosed incidentally when patients are being screened for another reason.¹¹ 

How is fibromuscular dysplasia diagnosed?

If a patient is suspected to have fibromuscular dysplasia (FMD), they must undergo a thorough vascular examination,⁴ which includes listening for bruits with a stethoscope.⁶

Imaging studies, such as computed tomography angiography (CTA) and magnetic resonance angiography (MRA)⁴ of the blood vessels, may be performed to confirm the diagnosis. However, CT angiography is often the preferred non-invasive test,⁵ as it reveals the classic ‘string-of-beads’ appearance.⁹

Conventional angiography, an invasive procedure involving catheter insertion to assess the arteries,¹³ is considered the definitive test (gold standard) for diagnosing FMD.

What is the differential diagnosis of fibromuscular dysplasia?

Some conditions that may be confused for fibromuscular dysplasia (FMD) include:¹

• Renal artery stenosis
• Marfan syndrome
• Tuberous sclerosis
• Alport syndrome
• Alpha-1 antitrypsin deficiency
• Ehlers-Danlos syndrome
• Neurofibromatosis type 1
• Takayasu arteritis

What are the causes and risk factors for fibromuscular dysplasia? 

The exact cause of fibromuscular dysplasia (FMD) remains unknown. However, the following are some of the risk factors associated with the development of FMD:^9,11 

• Tobacco use
• Having a family history of vascular problems
• Female gender: FMD is more commonly seen in women than men, with a female-to-male ratio of approximately 9:1
• Age between 20 and 50: FMD is most frequently diagnosed in individuals within this age range

How do you treat fibromuscular dysplasia?

Fibromuscular dysplasia (FMD) cannot be cured and requires management by a multidisciplinary team, with treatment tailored to the patient’s presenting symptoms. Treatment options range from regular monitoring to symptomatic treatment or surgical intervention. Medications may be prescribed to manage migraine headaches or control blood pressure.⁶ Similarly, patients at risk of developing a stroke may be prescribed antiplatelet drugs, such as aspirin.^9,11

In cases where an aneurysm is present, neurosurgical clipping or endovascular coiling are two techniques used to prevent an aneurysm rupture.⁷ In the case of an arterial blockage, treatment options include balloon angioplasty and stent insertion, which widen the affected artery and improve blood flow.⁶

Educating patients regarding lifestyle changes is also beneficial, such as eating a healthy and balanced diet, reducing salt (sodium) intake,⁵ quitting smoking, and maintaining a healthy weight. Patients should also be cautioned about neck manipulations and avoiding neck trauma.¹

What are the complications of fibromuscular dysplasia?

Some complications of fibromuscular dysplasia (FMD) include:

• Arterial dissection: For example, spontaneous coronary artery dissection (SCAD), which is a tear in the wall of the coronary artery (supplying blood to the heart)¹⁴
• Arterial aneurysm: For example, an aneurysm (artery bulge) in the brain
• Stroke or transient ischaemic attack (TIA): Patients with FMD may experience a stroke or TIA as a result of decreased blood flow to the brain caused by arterial dissection.¹⁰ Similarly, a stroke can result from the rupture and bleeding of an aneurysm into the brain¹² 

What is the prognosis of fibromuscular dysplasia?

The prognosis of fibromuscular dysplasia (FMD) largely depends on an early diagnosis. However, reaching an early diagnosis can be challenging because some patients remain asymptomatic, and many symptoms of FMD are non-specific, such as migraine-like headaches and dizziness. Nonetheless, many patients with FMD go on to live long, healthy lives.¹⁰

Summary

Fibromuscular dysplasia (FMD) is a rare condition of the arteries characterised by narrowing and abnormal thickening of the arterial walls, resulting in the classic ‘string-of-beads’ appearance. FMD most commonly affects the renal and carotid arteries, though it can involve other arteries in the body.

Symptoms of fibromuscular dysplasia vary depending on the artery or arteries that are involved, and it is common for multiple arteries to be affected. When the carotid arteries are affected, symptoms may include headaches, dizziness, and neck pain. When the renal arteries are involved, symptoms may include abdominal pain and hypertension.

Patients suspected of having fibromuscular dysplasia should undergo a thorough vascular examination, including checking for bruits. The diagnosis is confirmed with the help of imaging studies, such as computed tomography angiography (CTA) and magnetic resonance angiography (MRA). Catheter-based angiography remains the gold standard for diagnosis.

Treatment for fibromuscular dysplasia is primarily symptomatic. Physicians may prescribe medications for controlling hypertension and managing headaches. Patients at risk of stroke may benefit from antiplatelet drugs, such as aspirin. Endovascular repair or surgical intervention may be recommended for some patients.

The exact cause of fibromuscular dysplasia remains unknown, but it predominantly affects females, with a female-to-male ratio of approximately 9:1. Adults who are diagnosed with FMD tend to be between the ages of 20 and 50. Tobacco use and a family history of FMD are considered risk factors for developing the condition.

Complications of fibromuscular dysplasia can include dissection of the arteries, aneurysm rupture, and the development of a stroke or transient ischaemic attack (TIA). The prognosis of FMD depends on early diagnosis; however, many patients with FMD go on to live long, healthy lives.