Fibromuscular dysplasia

The main symptoms associated with renal FMD are secondary hypertension and bruits that can be heard with a stethoscope over the abdomen or flanks. Complications such as aneurysms, dissections, or occlusion of the renal artery have been associated with renal artery FMD.[4]

The carotid and vertebral arteries are most commonly affected. Middle and distal regions of the internal carotid arteries are frequently involved.[1] Patients with FMD in the carotid arteries typically present around 50 years of age.[3] Symptoms of craniocervical involvement include headaches (mostly migraine), pulsatile tinnitus, dizziness, and neck pain, although patients are often asymptomatic. On physical examination, one may detect neurological symptoms secondary to a stroke or transient ischemic attack (TIA), a bruit over an affected artery, and diminished distal pulses. Complications of cerebrovascular FMD include TIA, ischemic stroke, Horner syndrome, or subarachnoid hemorrhage.[1][2][3]

Patients with mesenteric, or intestinal FMD, may experience abdominal pain after eating or weight loss. FMD within the extremities may cause claudication or may be detectable by bruits.[1] If the lower limb arteries are affected, the patient may present with cold legs or evidence of distal embolic disease. FMD present in the subclavian artery may cause arm weakness, paresthesia, claudication, and subclavial steal syndrome.[6]

Children with FMD often report various non-specific symptoms or present with hypertension during routine physical examinations. Symptoms are commonly associated with the artery being affected. Symptoms may include headaches, insomnia, fatigue and chest or abdominal pain. FMD affecting the arteries of the head & neck is commonly recognized as a cause of childhood strokes.[7]

Detection may stem from a bruit being present over the affected vascular bed during a physical assessment. Yet, absence of a bruit does not rule out significant vascular disease.[8]

In children, renovascular disease accounts for approximately 10% of all causes of secondary hypertension.[8] Kidney failure is a common presentation in infants and children but is uncommon in adults, although it is occasionally the presenting problem in adults with focal disease.[3] “The presentation in infants and children younger than 4 years is especially likely to resemble vacuities.”[3]

The vascular subtype of Ehlers-Danlos Syndrome (type IV) has been associated with multi-focal FMD. This syndrome should be suspected in patients with multiple aneurysms and/or tears (dissections) in arteries in addition to the typical angiographic findings of FMD. There have been isolated reports of FMD associated with other disorders, including Alport syndrome, pheochromocytoma, Marfan syndrome, Moyamoya disease, and Takayasu's arteritis.[9]

In pediatrics, the most prevalent form of FMD is focal fibroplasia. Focal fibroplasia is described as long, narrow, irregular or smooth focal stenosis and can occur in any arterial bed. Whilst it is the most common type amongst children, it only accounts for approximately 10% of FMD cases overall.[8] It most often presents with ischemic symptoms, and frequently mistaken for Takayasu arteritis.[11] (previously known as intimal)

The second type, multi-focal fibroplasia, involves thickening of the media and collagen formation. It is typically reported as having the appearance of a ‘string of beads’ on angiographic review.[4] "The 'bead' component is often larger than the normal arterial lumen, and in a subset of patients with FMD, aneurysms are present that may require treatment."[4] The multi-focal subtype of FMD accounts for nearly 80% to 90% of all FMD cases.[4] (previously known as medial)

The third classification is adventitial fibroplasia, in which collagen replaces the fibrous adventitia and extends beyond the artery. This form is considered rare but angiographic appearance may look similar to the focal subtype of FMD, making the distinction difficult.

• In the visceral distribution, Segmental arterial mediolysis may mimic FMD.
• In the visceral and cerebrovascular distribution, atherosclerosis must be considered.

The differentiating presentations are suggestive of FMD being a unique syndrome in respect to the pediatric population. Experienced FMD clinicians warn against relying on the “string of beads” angiography for a diagnosis. In fact, it is suggested that FMD may be both under and over-diagnosed in children with stroke.[7]

Blood pressure control is the primary concern when treating patients with renal FMD since the ideal blood pressure target in patients with FMD is unknown.[10] In cases of renal artery stenosis and indications for intervention, percutaneous balloon angioplasty may be recommended. Many studies have assessed the success rate of percutaneous transluminal angioplasty (PTA) in these cases, and have found relief of hypertensive symptoms.[3][12] Duplex ultrasonography should be performed soon after this procedure to ensure adequate renal velocities.[3]

Stents have a restenosis rate of 10-20%, and may make surgical revascularization more difficult. Surgical revascularization may be necessary if aneurysms develop within the affected artery or if PTA does not resolve the issue.

Ex vivo renal artery reconstruction is sometimes used for complex diseases where branches of the renal artery are affected.[13]

Patients with carotid or vertebral FMD should be medically managed to reduce the risk of a stroke. Aspirin 81 mg is typically prescribed for patients with carotid FMD. Antiplatelets and anticoagulants may be used to reduce the risk of blood clot formation. If a TIA or stroke are to occur, percutaneous angioplasty and antiplatelet therapy may be necessary.[3] Pulsatile tinnitus is recognized as a common manifestation in 32% of US cerebrovascular FMD patients and sound or cognitive behavioral therapy may be helpful for some patients with more severe symptoms.[10]

Little information is known regarding the best treatment for FMD outside of the renal and extracranial regions. If claudication or limb ischemia is consequent to FMD in the extremities, angioplasty may be implemented.

Pediatric FMD medical and surgical treatments or interventions are available. Treatment is determined by factors such as age and disease location but routinely involve controlling hypertension, re-establishing vascular flow, clot prevention, and improving lifestyle such as diet, exercise and smoking cessation. Medical therapy for pediatric population may involve the use of angiotensin-converting enzyme inhibitor (ACE inhibitors) and/or angiotensin II receptor blockers, multiple anti-hypertensive medications, diuretics, calcium channel blockers, and beta-blockers. Prevention of thrombosis of affected arteries may be taken through administration of an antiplatelet medication such as aspirin.[1]

Percutaneous transluminal renal angioplasty (PTRA) remains the gold standard for renal-artery FMD. This treatment is useful when hypertension is difficult to control; patient is intolerant to the anti-hypertensive medications, non-complainant to medication regime and patient loss of renal volume due to ischemia. PTRA can also aid in preventing a lifelong dependency on medication for such a young patient. According to Meyers, “effective PTRAs result in cured or controlled blood pressure, which is often signified by reductions in plasma renin activity and angiotensin II levels, and when compared with surgery, percutaneous balloon angioplasty is less costly, able to be performed on an outpatient basis, results in lower morbidity, and the use of stenting is not primarily necessary.” However, there is a subset of the pediatric population that is resistant to PTRA. Adverse events may include, “recurrent stenosis, arterial occlusion with renal loss, and arterial rupture with extravasations and pseudo aneurysm formation and may require surgical intervention.