Clinical Manifestations and Diagnosis of Fibromuscular Dysplasia
Clinical Manifestations
FMD is a nonatherosclerotic, noninflammatory vascular disease that most commonly presents as hypertension in young to middle-aged women, though it can affect both genders at any age and involves multiple arterial territories throughout the body. 1
Renal Artery FMD (Most Common Presentation)
- Hypertension is the hallmark presentation, particularly in patients aged ≤35 years with new-onset hypertension 1, 2
- Severe hypotension or azotemia provoked by ACE inhibitors or ARBs suggests hemodynamically significant renal artery stenosis 1
- FMD characteristically involves the middle and distal two-thirds of the main renal artery and may extend into branches, unlike atherosclerotic disease which affects the ostial and proximal segments 1
- Medial fibroplasia accounts for 80-85% of renal FMD cases and typically affects both renal arteries in women aged 25-50 years 1
Cerebrovascular FMD (Equally Common)
- Stroke or transient ischemic attack (TIA) from reduced blood flow or thromboembolism 1
- Carotid or vertebral artery dissection, which can occur spontaneously 1
- Headaches and pulsatile tinnitus (described as a "swishing" sound in the ears) 3, 2
- Horner syndrome from carotid involvement 1
- Cranial nerve palsies 1
- Subarachnoid hemorrhage from aneurysmal rupture 1, 3
- The internal carotid arteries are most frequently involved, typically bilaterally 1
Other Vascular Territories
- Iliac arteries are commonly affected, requiring evaluation beyond the initially symptomatic site 4
- FMD can theoretically affect any medium-sized artery throughout the body 5, 6
- Aneurysm formation is a recognized complication requiring surveillance 4, 7
Physical Examination Findings
- Cervical bruit in young patients should raise suspicion for carotid FMD 2
- Gross pathological manifestations include arterial elongation, kinking, and coiling 1
Asymptomatic Presentation
- An increasing number of patients are discovered incidentally during imaging performed for other reasons 2
- Asymptomatic patients still require monitoring and antiplatelet therapy 1
Diagnostic Approach
Duplex ultrasonography is the recommended initial screening test for renal FMD, while CT angiography or MR angiography from head to pelvis should be performed at diagnosis to identify the systemic nature of the disease. 1, 4, 7
First-Line Screening Tests (Class I Recommendations)
- Duplex ultrasonography as the initial screening test for renal artery FMD 1, 4
- Computed tomographic angiography (CTA) in patients with normal renal function 1, 4
- Magnetic resonance angiography (MRA) as an alternative screening modality 1, 4
- Contrast-enhanced CTA, MRA, or catheter angiography are all useful for diagnosing cervical artery dissection 1
Gold Standard Diagnostic Test
- Catheter-based contrast angiography should be performed when clinical suspicion is high and noninvasive tests are inconclusive 4, 7
- This remains the definitive diagnostic modality for FMD 4
Characteristic Angiographic Findings
- "String of beads" appearance is pathognomonic for medial fibroplasia, where the diameter of the beading is larger than the normal arterial diameter 1, 8
- This pattern is seen in the middle to distal portions of affected arteries 1, 8
- Focal stenosis can occur with intimal fibroplasia, appearing as concentric or tubular narrowing similar to atherosclerotic disease 1
- Weblike lesions may obstruct flow 1
- Aneurysmal dilation can be present 1
Comprehensive Systemic Evaluation
- CT or MRI angiography from head to pelvis should be performed at diagnosis to identify involvement in multiple vascular beds, particularly carotid, vertebral, renal, and iliac arteries 7
- FMD is now recognized as a systemic arterial disease requiring evaluation beyond the initially symptomatic territory 4, 7
Laboratory Assessment
- Very elevated renin levels may raise suspicion for renovascular hypertension 4
- Assessment of 24-hour urinary sodium or sodium-to-creatinine ratio in morning urine may be helpful when evaluating for renovascular hypertension 4
- Renal artery Doppler ultrasound with bilateral assessment of renal arterial resistive index is recommended for suspected renovascular hypertension due to FMD 4
Tests NOT Recommended (Class III)
- Captopril renal scintigraphy should not be used for screening 4, 7
- Selective renal vein renin measurements are not recommended 4, 7
- Plasma renin activity is not useful as a screening test 4, 7
Surveillance Imaging
- Annual noninvasive imaging of the carotid arteries is reasonable initially to detect changes in disease extent or severity 1, 4, 7
- Imaging frequency may be reduced once stability has been confirmed over time 1, 4, 7
Critical Diagnostic Pitfalls to Avoid
- Never assume isolated disease—always evaluate multiple vascular beds since FMD is systemic 7
- The differential diagnosis is extensive and includes imaging artifacts and other arterial diseases such as vasculitis 5, 8
- Consider FMD in any young person with cervical bruit, pulsatile tinnitus, TIA, stroke, arterial dissection, or new-onset hypertension aged ≤35 years 2