Elevated CRP Does NOT Rule Out Fibromuscular Dysplasia
An elevated C-reactive protein does not make fibromuscular dysplasia less likely, because FMD is explicitly defined as a non-inflammatory arterial disease and CRP elevation in this clinical context more likely reflects a concurrent inflammatory process, infection, or the systemic stress response to severe hypertension rather than excluding FMD. 1
Why CRP is Irrelevant to FMD Diagnosis
FMD is Non-Inflammatory by Definition
- Fibromuscular dysplasia is characterized as a non-atherosclerotic, non-inflammatory disease affecting the arterial wall, most commonly involving the renal arteries in young women 1
- The pathology of medial fibroplasia (80-85% of FMD cases) involves alternating areas of thinned media and thickened fibromuscular ridges containing collagen, without any inflammatory component 1
- Even intimal fibroplasia, a less common variant, shows circumferential or eccentric collagen deposition with no lipid or inflammatory component 1
Your Clinical Scenario Strongly Suggests FMD
In your 25-year-old patient with:
- Severe episodic hypertension – classic presentation for FMD 1, 2
- Elevated plasma renin activity and aldosterone – consistent with renovascular hypertension from renal artery stenosis 2
- Normal adrenal imaging – excludes primary aldosteronism as the cause 1
- Young age and female gender – the demographic most affected by FMD 1, 3
This constellation makes FMD a leading diagnostic consideration regardless of CRP level. 1, 4
Alternative Explanations for Elevated CRP
Concurrent Processes That Raise CRP
- Severe hypertension itself can trigger systemic inflammatory markers as part of endothelial stress and acute cardiovascular strain
- Occult infection or inflammatory condition unrelated to the vascular pathology
- Takayasu's arteritis is the one renovascular disease that IS inflammatory and would elevate CRP, but it typically presents with constitutional symptoms, elevated ESR, and involves the aorta and proximal great vessels rather than the distal/mid renal artery segments characteristic of FMD 1
Distinguishing FMD from Inflammatory Vasculitis
- If you suspect Takayasu's arteritis instead of FMD, look for:
- Constitutional symptoms (fever, weight loss, malaise)
- Elevated ESR in addition to CRP
- Aortic involvement and proximal vessel stenoses
- Younger age of onset (typically teens to 30s, but with systemic illness) 1
- FMD patients are typically otherwise healthy young women who present with isolated hypertension, not systemic illness 1, 3, 2
Diagnostic Next Steps
Imaging to Confirm FMD
- Duplex ultrasonography as initial screening (Class I recommendation) 1, 5
- CT angiography or MR angiography for comprehensive vascular assessment, looking for the characteristic "string of beads" appearance in the middle and distal two-thirds of the renal artery 1, 5
- Catheter angiography remains the gold standard when noninvasive tests are inconclusive or when planning intervention 5, 6
Do NOT Use These Tests for FMD Screening
- Captopril renal scintigraphy, selective renal vein renin measurements, and isolated plasma renin activity are not recommended for FMD diagnosis (Class III recommendation) 5
- These tests lack sensitivity and specificity for renovascular hypertension screening 5
Common Pitfall to Avoid
Do not let an elevated inflammatory marker dissuade you from pursuing FMD workup in a young patient with severe hypertension and elevated renin/aldosterone. The non-inflammatory nature of FMD means CRP should be normal in uncomplicated cases, but its elevation does not exclude the diagnosis—it simply indicates you need to investigate the source of inflammation separately. 1, 4
If imaging confirms FMD, percutaneous transluminal renal angioplasty without stenting is the treatment of choice and can normalize blood pressure without need for lifelong antihypertensives. 5, 7, 2