What is the workup for fibromuscular dysplasia (FMD)?

Workup of Fibromuscular Dysplasia (FMD)

The comprehensive workup for fibromuscular dysplasia should include vascular imaging with computed tomographic angiography (CTA) or magnetic resonance angiography (MRA) from head to pelvis, as FMD is now recognized as a systemic disease affecting multiple vascular beds. 1

Initial Diagnostic Approach

• Duplex ultrasonography is recommended as an initial screening test for FMD (Class I recommendation), particularly for renal artery evaluation 1
• CTA and MRA are recommended as primary screening tests for FMD (Class I recommendation) 1
• CTA has superior sensitivity (84.2%) compared to MRA (62.5%) and ultrasound (28%) for detecting FMD lesions 2
• Catheter-based angiography remains the gold standard for diagnosing FMD and should be performed when clinical suspicion is high but noninvasive tests are inconclusive 1, 3
• Catheter angiography is particularly important for detecting distal vessel disease that may be missed by other imaging modalities 2

Comprehensive Vascular Assessment

• FMD is a systemic arterial disease with potential involvement of multiple vascular beds, requiring evaluation beyond the initially symptomatic site 1, 3
• The most commonly affected arteries include:
  • Renal arteries (most common site, presenting as renovascular hypertension) 3
  • Carotid and vertebral arteries (cervicocranial FMD) 3
  • Iliac arteries 4
• Annual non-invasive imaging of the carotid arteries is reasonable initially for patients with FMD to detect changes in disease extent or severity (Class IIa recommendation) 4
• Imaging studies may be repeated less frequently once stability has been confirmed 4

Specific Imaging Findings

• The classic "string-of-beads" appearance (multiple stenoses) is observed in more than 80% of cases, representing medial FMD 3, 5
• Less common imaging findings that should prompt consideration of FMD include:
  • Vascular loops and fusiform vascular ectasia 5
  • Arterial dissection 5
  • Aneurysm formation 1, 5
  • Subarachnoid hemorrhage 5

Laboratory Assessment

• The American Heart Association does not recommend captopril renal scintigraphy, selective renal vein renin measurements, or plasma renin activity as screening tests for FMD (Class III recommendation) 1
• Assessment of sodium intake (24-hour urinary sodium or sodium-to-creatinine ratio in morning urine) may be helpful when evaluating for renovascular hypertension 4

Special Considerations

• For patients with suspected renovascular hypertension due to FMD:
  • Very elevated renin levels may raise suspicion for renovascular hypertension 4
  • Renal artery Doppler ultrasound with bilateral assessment of renal arterial resistive index is recommended 4
• In pediatric patients with suspected FMD:
  • Angiography should be performed as part of the initial workup regardless of findings on ultrasound, MRA, or CTA 2
  • Family history of hypertension (52%) and headache (48%) are common presenting features 2

Diagnostic Pitfalls

• FMD is often underdiagnosed, and delayed diagnosis may lead to refractory hypertension 2
• FMD can mimic vasculitis and should be considered in the differential diagnosis of systemic vascular disease, particularly in young to middle-aged females 6
• Bruits are 100% specific for renal artery stenosis but are heard in only a minority of patients (12%) 2
• FMD lesions are typically truncal or distal, whereas atherosclerotic lesions are more often proximal or ostial 7

By following this comprehensive diagnostic approach, clinicians can effectively identify and characterize FMD, enabling appropriate management and reducing the delay between symptom onset and diagnosis.