In a 25‑year‑old with severe episodic hypertension, elevated plasma renin activity and aldosterone, and normal adrenal imaging, does a modestly elevated C‑reactive protein that rises during a flare exclude renal‑artery fibromuscular dysplasia (FMD)?

Modestly Elevated CRP Does Not Exclude Renal Artery FMD in Young Patients with Renovascular Hypertension

A modestly elevated and fluctuating C-reactive protein (CRP 8.9-17.5 mg/L) does not exclude fibromuscular dysplasia (FMD) as the cause of renovascular hypertension in a 25-year-old with severe episodic hypertension, elevated renin, and elevated aldosterone—FMD remains the most likely diagnosis and should be actively pursued with renal artery imaging.

Why FMD Remains the Primary Diagnosis

Clinical Profile Strongly Suggests FMD

• Age and demographics are classic for FMD: This condition develops most commonly in patients <50 years of age, particularly young women, and accounts for <10% of renal artery stenosis cases overall but is the predominant cause in young adults 1.

• The biochemical profile is characteristic: Elevated plasma renin activity and aldosterone concentration in the setting of severe hypertension indicates renin-angiotensin-aldosterone system (RAAS) overactivation from renal artery stenosis 2, 3. Young patients with FMD commonly present with markedly elevated renin and secondary hyperaldosteronism 4, 5, 6.

• Episodic severe hypertension fits the pattern: FMD can cause paroxysmal hypertensive episodes, particularly when stenosis is hemodynamically significant 3.

CRP Elevation Does Not Rule Out FMD

• FMD is non-inflammatory by definition: Unlike atherosclerotic renal artery stenosis or vasculitis (such as Takayasu arteritis), FMD is characterized as an idiopathic, non-atherosclerotic, and non-inflammatory stenotic lesion 2.

• Modest CRP elevation can occur with FMD for other reasons: The CRP values you describe (8.9-17.5 mg/L) are modestly elevated, not dramatically high. This level of elevation can occur with:

  • Hypertensive stress and endothelial activation 1
  • Secondary effects of RAAS overactivation 2
  • Concurrent minor illness or physiologic stress
  • The "flare" itself causing sympathetic activation

• CRP rising during a hypertensive flare is expected: The temporal association between CRP rise (to 17.5) and the hypertensive flare likely reflects the acute cardiovascular stress and inflammatory response to severe blood pressure elevation, not an underlying inflammatory arteriopathy 4.

When to Suspect Inflammatory Arteritis Instead

Takayasu Arteritis Would Present Differently

• Much higher CRP and systemic inflammation: Takayasu arteritis typically presents with markedly elevated inflammatory markers, constitutional symptoms, and evidence of large-vessel inflammation on imaging (thickened aortic wall on CT, vessel wall enhancement on MRI) 4.

• Different anatomic distribution: Takayasu causes stenosis in the proximal renal artery (near the aortic origin), whereas FMD typically affects the mid-to-distal renal artery with characteristic "string-of-beads" appearance 4, 2.

• Age makes Takayasu less likely: While Takayasu can occur in young adults, the absence of other large-vessel involvement, constitutional symptoms, or dramatically elevated inflammatory markers makes this diagnosis unlikely 4.

Recommended Diagnostic Approach

First-Line Imaging for Renal Artery Stenosis

1. Renal duplex Doppler ultrasound is the most appropriate initial screening test (rated 9/9 "usually appropriate") as it is non-invasive, requires no contrast, and can detect hemodynamically significant stenosis 1.

2. MR angiography (MRA) without contrast is also highly appropriate (rated 7/9) and can visualize the characteristic mid-to-distal renal artery involvement and "string-of-beads" appearance of FMD 1, 2, 3.

3. CT angiography is effective but involves radiation and iodinated contrast, making it less ideal as a first choice in a young patient 1.

Confirmatory Testing

• Conventional renal angiography remains the gold standard for definitive diagnosis and allows for simultaneous therapeutic intervention (percutaneous transluminal renal angioplasty, PTRA) if FMD is confirmed 4, 2, 3.

• Radionuclide renal scintigraphy can document asymmetric kidney function and help predict response to revascularization 2.

Expected Outcomes with FMD Treatment

PTRA is Highly Effective in Young Patients with FMD

• Blood pressure normalization occurs rapidly: Case series demonstrate that successful angioplasty in FMD patients results in rapid normalization of blood pressure, often allowing discontinuation of antihypertensive medications 4, 2, 3.

• Biochemical abnormalities resolve: Plasma renin activity, aldosterone concentration, and hypokalemia (if present) normalize quickly after successful revascularization 4, 2, 5.

• End-organ damage reverses: Left ventricular hypertrophy and albuminuria can regress within months of successful treatment, indicating reversal of RAAS-mediated organ damage 2.

Critical Pitfalls to Avoid

• Do not delay imaging based on CRP levels: Waiting for CRP to normalize or attributing the hypertension to an inflammatory process will delay diagnosis and treatment of a highly treatable condition 4, 2.

• Normal adrenal imaging does not exclude secondary hyperaldosteronism: The elevated aldosterone in this case is secondary to high renin from renal artery stenosis, not primary adrenal disease. This is a renin-driven process 2, 3, 5, 6.

• Do not assume atherosclerotic disease: The young age and absence of cardiovascular risk factors make atherosclerotic renal artery stenosis (which accounts for 90% of cases overall) extremely unlikely in this patient 1, 2.

• Recognize that not all FMD shows "string-of-beads": While the classic medial fibroplasia subtype shows this appearance, other FMD subtypes (intimal, perimedial) may show focal tubular stenosis without beading 4, 2.