What is the initial workup for a patient suspected of having fibromuscular dysplasia (FMD)?

Workup for Suspected Fibromuscular Dysplasia

Begin with non-invasive vascular imaging using CTA from skull vertex to pelvis as the preferred initial diagnostic test, followed by catheter angiography if clinical suspicion remains high despite negative or equivocal non-invasive imaging. 1, 2

Initial Imaging Strategy

First-Line Imaging

• Computed tomographic angiography (CTA) is the recommended initial screening test (Class I recommendation), offering comprehensive evaluation of multiple vascular beds in a single session 1
• A single-acquisition CTA protocol covering skull vertex to pelvis is optimal, reducing radiation dose by 38% and contrast dose by 39% compared to separate imaging sessions while maintaining diagnostic quality 3
• CTA provides excellent visualization of the characteristic "string of beads" appearance and can detect arterial stenosis, aneurysms, dissections, and tortuosity 4, 5

Alternative Non-Invasive Options

• Magnetic resonance angiography (MRA) is also a Class I recommended screening test, particularly useful when radiation exposure is a concern 1
• Duplex ultrasonography with B-flow and B-mode imaging can identify arterial wall abnormalities, including isoechoic ridges protruding into the lumen and fusiform dilations characteristic of FMD 1, 6
• However, ultrasound has significantly lower sensitivity (28%) compared to angiography and should not be relied upon as the sole imaging modality 2

Gold Standard Confirmation

• Catheter-based angiography remains the gold standard and should be performed when clinical suspicion is high and non-invasive tests are inconclusive or negative 1, 2
• Angiography is particularly critical for detecting distal vessel disease beyond second-order branches, which may be missed on CTA or MRA 2
• In pediatric cases, angiography should be part of the initial workup regardless of non-invasive imaging findings 2

Laboratory Assessment

Blood Pressure and Renal Function

• Measure blood pressure in both arms to detect asymmetry 1
• Obtain basic metabolic panel including serum creatinine and electrolytes 1
• Assess 24-hour urinary sodium or sodium-to-creatinine ratio in morning urine when evaluating for renovascular hypertension 1
• Measure plasma renin levels, as very elevated levels may raise suspicion for renovascular hypertension, though this is not recommended as a screening test 1

Renal-Specific Testing

• Perform renal artery Doppler ultrasound with bilateral assessment of renal arterial resistive index for suspected renovascular hypertension due to FMD 1
• Do NOT use captopril renal scintigraphy or selective renal vein renin measurements as screening tests (Class III recommendation) 1

Physical Examination Findings

Key Clinical Features

• Listen for vascular bruits, particularly in the periumbilical area and flanks, though bruits are only present in a minority of patients (12%) but are 100% specific for renal artery stenosis when present 2
• Check for signs of end-organ ischemia depending on vascular bed involvement 4
• Document any neurological symptoms including headache (present in 48% of cases), which may indicate carotid or vertebral involvement 2

Comprehensive Vascular Bed Evaluation

Systemic Disease Assessment

• FMD is a systemic disease requiring evaluation of multiple arterial territories, not just the initially symptomatic site 1
• The iliac arteries are commonly affected and require evaluation beyond the initially symptomatic site 1
• Annual non-invasive imaging of carotid arteries is reasonable initially (Class IIa recommendation) to detect disease progression, with less frequent imaging once stability is confirmed 7, 1

Distribution Patterns

• FMD is mainly unifocal within a single site (68%) or involves multiple sites (28%) 2
• The main or first-order renal branch is involved in approximately 68% of cases 2
• Isolated distal lesions beyond second-order branches occur in about 25% of cases 2

Common Pitfalls to Avoid

• Do not rely solely on duplex ultrasound for diagnosis, as it has only 28% sensitivity compared to angiography 2
• Do not skip catheter angiography in pediatric patients with suspected FMD, even if CTA or MRA appears normal, as distal disease may be missed 2
• Do not limit imaging to a single vascular bed, as FMD commonly affects multiple arterial territories including renal, carotid, vertebral, and iliac arteries 1, 4
• Recognize that MRA has better sensitivity (62.5%) than ultrasound but CTA has the best non-invasive sensitivity (84.2%) compared to angiography 2