Fibromuscular dysplasia

Fibromuscular dysplasia (FMD), a disease that primarily affects young to middle-aged women, is characterized by the proliferation of connective tissue and muscle fibers within the arterial vessel walls. The resulting stenosis impairs perfusion of the affected organ, causing ischemia. The symptoms of fibromuscular dysplasia vary depending on the site and the degree of stenosis of FMD. The renal, internal carotid, and vertebral arteries are predominantly involved. Carotid and vertebral artery involvement may present with transient ischemic attack (TIA) and/or stroke, while patients with renal FMD usually present with secondary hypertension and chronic renal insufficiency. Bruits at the costovertebral angle and the carotid region are characteristic findings of renal and carotid artery involvement respectively. In rare cases, patients may present with mesenteric ischemia and/or peripheral artery disease as a result of splanchnic or peripheral arterial involvement. The “string of beads” sign, a characteristic finding on angiography, distinguishes FMD from other causes of arterial occlusion. All patients with renal FMD should be treated with ACE inhibitors and/or ARBs, while those with carotid artery involvement should be placed on stroke prophylaxis (low-dose aspirin therapy). Balloon angioplasty without stenting is the definitive treatment.

• Age of onset: typically 30–50 years, but can manifest at any age
• Sex: : ♀ > ♂ (8:1)
  • Among children: ♀ ≈ ♂
• Ethnicity: increased prevalence among the white population

References:^[1][2][3][4]

Epidemiological data refers to the US, unless otherwise specified.

Fibromuscular dysplasia (FMD) is an idiopathic, non-inflammatory, non-atherosclerotic, developmental condition that primarily affects small and medium-sized muscular arteries.

Histopathology

The most commonly encountered histology is medial fibroplasia.

Pathophysiology

• FMD results in ischemia by one or more of the following mechanisms:
  • Stenosis
  • Formation of saccular aneurysms → aneurysmal rupture
  • Arterial dissection → arterial occlusion
  • Formation of intravascular thrombi → embolization
• Renal artery stenosis → ↓ renal perfusion → compensatory activation of the renin–angiotensin–aldosterone system → secondary hypertension

Disease localization

• Renal artery (renal FMD; ∼ 75–80% of cases)
  • Usually bilateral renal artery stenosis
  • Second most common cause of renal artery stenosis after atherosclerosis.
  • Accounts for 30–50% of cases of renal artery stenosis among children and 5–10% of cases among adults.
• Carotid and vertebral artery involvement (extracranial cerebrovascular FMD; ∼ 65–75% of cases and often bilateral)

References:^{[1][1][2][3][4][5][5][5]}

The symptoms of fibromuscular dysplasia are nonspecific and vary depending on the site of FMD, the degree of stenosis, and the underlying pathology (e.g., arterial dissection).

• Renal FMD
  • Clinical features of renal artery stenosis
    • Secondary hypertension
    • Abdominal bruit
    • Symptoms of chronic kidney disease
  • Flank or abdominal pain
• Cerebrovascular FMD
  • Headache, neck pain, pulsatile tinnitus
  • TIA, amaurosis fugax, stroke, Horner's syndrome
  • Cervical bruit

References:^{[1][1][2][3][5][5][5]}

• Imaging
  • Imaging modalities
    • Best initial tests for renal FMD: duplex ultrasonography and/or CT angiography (see “Diagnostics” in renal artery stenosis)
    • Best initial tests for cerebrovascular FMD: CT angiography
    • Gold standard: digital subtraction angiography (DSA)
  • Finding
    • Common finding: “string of beads” sign
    • Less commonly: a single, circumferential/tubular stenotic lesion
• Laboratory tests: serum creatinine

References:^[2][3]

• Atherosclerosis
  • Patients with atherosclerosis are usually older, male, and have risk factors such as obesity and/or cigarette smoking.
  • On angiography, atherosclerosis affects the proximal segments and ostia of arteries, while FMD affects middle and distal segments of the artery.
• Vasculitis (e.g., giant cell temporal arteritis; , PAN)

The differential diagnoses listed here are not exhaustive.

• Renal artery FMD: see “Therapy” in renal artery stenosis
• Cerebrovascular FMD
  • Antiplatelet drugs (e.g., aspirin) for stroke prophylaxis is recommended for all patients.
  • Patients who are symptomatic: percutaneous transluminal angioplasty

References:^[6][7][8]