Polyarteritis Nodosa

Medical Disclaimer

This comprehensive clinical reference is provided for informational and educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Clinicians must exercise independent judgment and integrate this information with patient-specific factors, local resources, and current institutional protocols. Medical decisions must always prioritize patient safety and adhere to established ethical and legal standards.

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Overview

Definition

Polyarteritis Nodosa (PAN) is a necrotizing vasculitis of medium-sized muscular arteries (and occasionally small arteries), characterized by segmental, transmural inflammation leading to luminal occlusion, aneurysms, and subsequent tissue ischemia or infarction. It spares capillaries, arterioles, and venules, and typically lacks major involvement of the lung parenchyma.

Epidemiology

• Incidence: Rare; estimated incidence is 1–2 cases per million population per year.
• Prevalence: Decreasing in recent decades, possibly due to better control of underlying etiologies (e.g., Hepatitis B).
• Age: Predominantly affects adults, classically in the 40s and 50s.
• Sex: Slightly more common in males (Male:Female ratio approximately 1.5:1).
• Associated Conditions: A subset of PAN is strongly associated with Chronic Hepatitis B Virus (HBV) infection, known as HBV-associated PAN.

Classification

PAN is generally classified by etiology:

1. Classic Polyarteritis Nodosa (cPAN): Idiopathic, the original description of the disease.
2. Secondary PAN:
   • HBV-associated PAN: Accounts for a significant proportion historically, especially in endemic areas.
   • Related to other infections: Less commonly, Hepatitis C, HIV, or Parvovirus B19.
   • Related to underlying malignancy or auto-immune conditions (though overlaps with other vasculitides must be excluded).
3. Cutaneous Polyarteritis Nodosa (cPAN): A localized form limited to the skin and subcutaneous tissues, typically having a better prognosis and rarely progressing to systemic disease.

Pathophysiology

Mechanism

PAN is an immune-mediated disorder leading to vascular damage:

1. Vascular Target: Medium-sized arteries are primarily affected, often at bifurcations.
2. Inflammation: Segmental, transmural inflammation involves the entire vessel wall, leading to fibrinoid necrosis. The inflammatory infiltrate consists primarily of neutrophils, lymphocytes, and macrophages.
3. Damage Cascade: The necrosis and inflammation weaken the vessel wall, leading to the formation of microaneurysms (the "nodosa" characteristic upon angiography/pathology).
4. Ischemia: Healing or chronic damage results in intimal proliferation, thrombosis, and luminal narrowing/occlusion, causing organ ischemia and infarction distal to the affected segment.
5. Immune Complexes: In HBV-associated PAN, circulating immune complexes (HBV antigens and host antibodies) deposit in the vessel walls, initiating the complement cascade and inflammatory response. This mechanism is less clear in idiopathic PAN.

Risk Factors

• Infection: Chronic Hepatitis B infection is the most robustly linked risk factor.
• Age: Middle age (40–60 years).
• Environmental/Occupational: Exposure to certain chemicals has been hypothesized but not definitively proven.
• Genetic Susceptibility: Currently poorly defined, but likely involves specific human leukocyte antigen (HLA) types.

Protective Factors

• Vaccination against HBV: Effective prevention of HBV infection reduces the primary risk factor for secondary PAN.
• Effective Anti-viral Therapy: Early and sustained clearance of HBV infection decreases the risk of developing HBV-associated PAN.

Clinical Presentation

PAN is a multisystem disease lacking a pathognomonic clinical feature, often presenting with vague systemic symptoms and culminating in signs of severe organ ischemia.

Signs and Symptoms

System	Cardinal Features	Rationale
Systemic	Fever of unknown origin, profound fatigue, weight loss (>4 kg)	General inflammatory response and cytokine release.
Musculoskeletal	Arthralgias (non-deforming), Myalgias	Muscle and joint inflammation or ischemia (infarction).
Neurologic (80%)	Mononeuritis multiplex (most common), foot drop, wrist drop	Ischemic damage to the vasa nervorum (medium arteries supplying nerves).
Gastrointestinal (50%)	Abdominal pain (often postprandial), unexplained acute abdomen, GI bleeding	Ischemia/infarction of the mesenteric arteries, leading to bowel perforation or infarction.
Renal (70%)	Hypertension (new-onset or severe), Renal insufficiency (non-glomerular)	Ischemia due to narrowing of medium-sized renal arteries; Renovascular hypertension is key.
Dermatologic (60%)	Livedo reticularis (pathognomonic if severe), subcutaneous nodules/painful lumps, skin ulcers, digital gangrene	Ischemia of dermal and subcutaneous arteries.
Cardiovascular (20%)	Myocardial infarction, congestive heart failure	Ischemia of coronary arteries.
Ocular/Otolaryng.	Episcleritis, scleritis, sudden hearing loss, vertigo (due to inner ear ischemia)	Ischemia of vessels supplying these structures.

Early Signs

• Unexplained fever and malaise.
• New-onset severe hypertension, often refractory to initial medications.
• Isolated pain in a nerve distribution (e.g., sensory/motor changes in the foot).

Advanced Signs

• Acute abdomen requiring urgent surgical exploration (bowel perforation/infarction).
• Acute limb ischemia leading to gangrene.
• Rapidly deteriorating renal function (if bilateral renal artery involvement).

Atypical Presentations

• Testicular pain/epididymitis (due to testicular artery involvement).
• Purely cutaneous involvement (Cutaneous PAN).

Physical Examination

Inspection

• Skin: Observe for livedo reticularis (a net-like purple mottling, especially on the extremities and trunk), subcutaneous nodules (tender, palpable segments of vasculitis), and digital tip ischemia/gangrene.
• Fundoscopy: May reveal ischemic changes or hypertensive retinopathy.
• General: Signs of weight loss, cachexia, or distressed appearance.

Palpation

• Abdomen: Tenderness, guarding, or rebound suggesting peritonitis (bowel ischemia).
• Pulses: Peripheral pulses are usually preserved unless large adjacent vessels (rarely involved) or severe distal thrombosis occurs.
• Nodules: Palpate subcutaneous nodules.
• Testes: Tenderness suggesting involvement of the testicular artery.

Special Tests

• Neurologic Exam: Rigorous testing for strength and sensation to document mononeuritis multiplex, critical for diagnosis and monitoring.

Diagnostic Approach

The diagnosis of PAN is established based on a combination of clinical features, exclusion of other vasculitides, laboratory findings (showing inflammation), and, critically, demonstration of medium-vessel vasculitis via biopsy or characteristic angiography findings.

History Taking

Key Questions

• Systemic Symptoms: Duration and severity of fever, weight loss, and fatigue.
• HBV Exposure: History of Hepatitis B infection, vaccination status, family history.
• Neurological: Presence of numbness, tingling, weakness, or specific nerve deficits (e.g., difficulty lifting the foot/wrist).
• Abdominal: Timing and character of abdominal pain, relation to meals, history of GI bleeding.
• Malignancy/Drug Use: Rule out secondary causes of vasculitis (e.g., cocaine-induced midline destructive lesions, malignant underlying disease).

Red Flags (Requiring Urgent Management)

• Acute severe abdominal pain or signs of peritonitis.
• Acute, rapidly developing neurological deficits (e.g., stroke, severe mononeuritis multiplex).
• Malignant hypertension (BP >180/120 mmHg) with end-organ damage.
• New or rapidly worsening renal failure.

Laboratory Tests

First-Line

• Complete Blood Count (CBC): Often shows normocytic, normochromic anemia (anemia of chronic disease) and leukocytosis.
• Inflammatory Markers: Erythrocyte Sedimentation Rate (ESR) and C-Reactive Protein (CRP) are typically markedly elevated (often >100 mm/h for ESR).
• Renal Function: Blood Urea Nitrogen (BUN) and Creatinine (Cr) to assess kidney function.
• Liver Function Tests (LFTs): To assess for HBV or drug toxicity.
• Urinalysis: May show mild proteinuria or hematuria, but the classic glomerulonephritis findings associated with ANCA-associated vasculitis (AAV) are absent.
• Infectious Workup:
  • Hepatitis B Serology: HBsAg, anti-HBs, HBeAg, anti-HBe, HBV DNA viral load (Crucial).
  • Hepatitis C and HIV testing.

Confirmatory/Exclusionary

• Antineutrophil Cytoplasmic Antibodies (ANCA): Negative or non-specific PR3-ANCA/MPO-ANCA titers are expected. Positive ANCA suggests AAV (e.g., MPA, GPA) and virtually excludes idiopathic PAN.
• Immunologic Workup: Anti-nuclear antibodies (ANA), Rheumatoid Factor (RF), Cryoglobulins (usually negative; rule out cryoglobulinemic vasculitis).
• Complement Levels (C3, C4): May be low in HBV-associated PAN (due to immune complex consumption) but usually normal in idiopathic PAN.

Monitoring

• ESR and CRP are used to track disease activity and response to therapy.
• Regular LFTs and renal panels to monitor for drug toxicity.
• HBV viral load (for HBV-associated PAN) to monitor anti-viral treatment efficacy.

Imaging

Recommended

• Conventional Angiography (Digital Subtraction Angiography - DSA): Considered the gold standard for non-invasive diagnosis when biopsy is impractical or negative.
  • Findings: Classic findings are multiple saccular aneurysms (microaneurysms, usually 1–5 mm) in medium-sized arteries, often affecting the renal, hepatic, and mesenteric circulations. These aneurysms undergo cycles of formation, thrombosis, and resolution, often leading to vessel cutoffs/stenoses.
• CT Angiography (CTA) or MR Angiography (MRA): Increasingly used as less invasive alternatives. High-resolution CTA can often visualize the aneurysms, especially in the abdominal vessels.

Advanced

• Biopsy (Definitive Confirmatory Test): Necessary if angiography is non-diagnostic or if results conflict with the clinical picture.
  • Preferred Sites: Symptomatic sites (e.g., skin, nerve/muscle, kidney, testicle) offer the highest yield.
  • Histopathology: Shows segmental, transmural inflammation and fibrinoid necrosis of the arterial wall. Evidence of mixed inflammatory infiltrate and vessel wall destruction. Crucially, the absence of glomerulonephritis excludes most AAV.

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Management

Management of PAN depends heavily on disease severity (typically assessed using the Five-Factor Score [FFS]) and the presence of underlying HBV infection.

Acute Management

Immediate

• Rule out Infection/HBV: Start aggressive workup, as treatment differs significantly.
• High-Dose Glucocorticoids: Initiate immediately upon high clinical suspicion for systemic disease affecting critical organs.

Stabilization

• Control Hypertension: Aggressive management of renovascular hypertension is critical to prevent stroke or kidney damage.
• Pain/Analgesia: Manage severe painful ischemia, especially mononeuritis multiplex.

Emergency

• Bowel Perforation: Urgent surgical consultation for acute abdomen.
• Severe Renal Insufficiency/Malignant HTN: Consider prompt initiation of therapy (corticosteroids + cyclophosphamide or aggressive anti-viral therapy).

Chronic Management (Based on FFS Criteria)

The FFS predicts prognosis and guides initial immunosuppressive intensity. Criteria: renal insufficiency (Cr >1.6 mg/dL), proteinuria (>1 g/day), gastrointestinal tract involvement, cardiomyopathy, or central nervous system involvement.

FFS Score	Risk Stratification	Recommended Initial Therapy
FFS = 0	Mild/Intermediate	Glucocorticoids (GC) alone, possibly with azathioprine/methotrexate for GC tapering.
FFS ≥ 1	Severe/Life-Threatening	Glucocorticoids + Cyclophosphamide.
HBV-associated PAN	Specific Treatment	Glucocorticoids + Antiviral Therapy (Avoid Cyclophosphamide initially).

Pharmacological Treatment

1. Glucocorticoids (GC)

• Dose: Prednisone oral 1 mg/kg/day (maximum 60–80 mg/day) for systemic disease.
• Duration: Maintained for 4–6 weeks, then a slow taper over 6–12 months based on clinical response and inflammatory markers (ESR/CRP).
• Pulse Therapy: For critically ill patients with rapidly progressing disease or major organ failure (e.g., methylprednisolone 500–1,000 mg IV daily for 3 days).

2. Immunosuppressants (for Idiopathic PAN, FFS ≥ 1)

• Cyclophosphamide (CYC): Used for induction in severe, life-threatening disease.
  • Dosing:
    • IV Pulse: 0.6–1.0 g/m² every 3–4 weeks for 3–6 pulses.
    • Oral: 2 mg/kg/day.
  • Goal: Achieve remission. Typically, CYC is discontinued or switched to a less toxic agent (e.g., azathioprine) upon sustained remission (usually 3–6 months).

3. Maintenance Therapy (After Remission)

• Azathioprine (AZA): 2 mg/kg/day. Preferred for transitioning off CYC and long-term maintenance.
• Methotrexate (MTX): 15–25 mg weekly (if renal function is adequate, Cr clearance >60 mL/min).
• Mycophenolate Mofetil (MMF): Becoming an acceptable alternative to AZA/MTX, 1–2 g/day.

4. Treatment of HBV-associated PAN (Specific Algorithm)

The goal is rapid HBV viral clearance, making the vasculitis therapy fundamentally different. Immunosuppression must be reduced/avoided if possible, as it can exacerbate HBV replication. * Initial Therapy: Low-dose Glucocorticoids (to control acute symptoms) + Aggressive Antiviral Therapy. * Antivirals: Potent and safe options like Tenofovir (300 mg daily) or Entecavir (0.5–1.0 mg daily). * Plasma Exchange (PLEX): Highly effective in severe HBV-associated PAN to remove circulating immune complexes and is recommended alongside antivirals to bridge the gap until HBV clearance. * Rationale: Once the viral antigens are cleared, the immune complex formation and subsequent vasculitis resolve. Immunosuppression (especially CYC) is usually deferred unless urgent life-threatening disease is unresponsive to PLEX and antivirals.

Treatment Algorithms

First-Line (Idiopathic PAN, FFS ≥ 1)

1. High-dose GC + Pulse CYC induction (3–6 months).
2. Taper CYC and transition to AZA/MTX/MMF for maintenance (12–18 months total maintenance).

Second-Line (Idiopathic PAN)

• Rituximab (Anti-CD20): Emerging evidence supports use in induction therapy, particularly for patients intolerant to CYC, or as a maintenance agent, similar to its role in AAV.

Refractory Cases

• If failure to achieve remission after 6 months of CYC and GC, consider:
  • Other immunosuppressants (e.g., MMF, anti-TNF agents, or biologics).
  • Exploratory angiography to rule out aneurysmal rupture or significant thrombotic occlusion requiring intervention.

Non-pharmacological (Supportive Care)

• Hypertension Management: Aggressive use of appropriate antihypertensives (ACE inhibitors/ARBs must be used cautiously if bilateral renal artery stenosis is suspected or confirmed).
• GI Involvement: Nutritional support and careful monitoring for evidence of infarction/perforation.
• Infection Prophylaxis: Pneumocystis jirovecii pneumonia (PJP) prophylaxis (e.g., trimethoprim/sulfamethoxazole) for patients on high-dose GC or CYC.

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Complications

Common

• Neuropathy (Mononeuritis multiplex), leading to functional deficits.
• Uncontrolled hypertension.
• Chronic pain and fatigue.

Serious

• Bowel Infarction or Perforation: High mortality rate.
• Aneurysm Rupture: Especially in the renal or hepatic circulation, causing catastrophic hemorrhage.
• Myocardial Infarction or failure due to coronary arteritis.
• Renal failure requiring dialysis.

Long-term

• Relapse (occurs in 10–20% of patients within 5 years).
• Chronic end-organ damage (e.g., permanent peripheral neuropathy, chronic renal insufficiency).
• Infection and malignancy risk due to chronic immunosuppression (especially hemorrhagic cystitis/bladder cancer from cumulative CYC).

Prognosis

Factors Affecting Outcome

The Five-Factor Score (FFS) is the primary prognostic tool (developed primarily for AAV but applied to PAN). Higher FFS indicates worse prognosis.

Poor Prognostic Factors: 1. Renal insufficiency (Cr >1.6 mg/dL). 2. Proteinuria >1 g/day. 3. GI involvement. 4. Cardiomyopathy. 5. CNS involvement.

Survival

• Untreated PAN is associated with severe morbidity and mortality (5-year survival approx. 10%).
• With modern treatment protocols (GC + CYC, or antiviral/PLEX), the 5-year survival rate for idiopathic PAN has significantly improved to approximately 80%.
• Prognosis for cutaneous PAN is excellent.

Quality of Life

QoL is often reduced due to: * Side effects of long-term immunosuppression (infection, diabetes, osteoporosis). * Residual organ damage, particularly peripheral neuropathy. * Chronic fatigue and pain associated with sustained low-level inflammation.

Prevention

Primary

• HBV Vaccination: Preventing Hepatitis B greatly reduces the risk of the most common secondary form of PAN.

Secondary

• Early Diagnosis: High index of suspicion crucial when unexplained fever, weight loss, mononeuritis multiplex, and severe hypertension occur simultaneously.
• Aggressive Antiviral Therapy: In HBV carriers, maintaining viral suppression may prevent progression to vasculitis.

Tertiary

• Adherence to Immunosuppression Protocols: Preventing relapses is critical for minimizing cumulative organ damage.
• Cardiovascular Risk Factor Management: Control blood pressure and lipids aggressively to mitigate additional ischemic damage on already compromised vessels.

Special Populations

Pediatric

• PAN in children is exceptionally rare and often mimics Kawasaki Disease (KD), which is a common differential; however, PAN typically involves larger arteries and lacks the classic mucosal findings of KD.
• Treatment: Similar aggressive immunosuppression (GC + CYC) is generally required for systemic disease.

Geriatric

• Increased susceptibility to infections and osteoporosis from GC and CYC.
• CYC dosing often requires adjustment based on age and declining renal function.
• Increased risk of cardiovascular complications from untreated renovascular hypertension.

Pregnancy

• PAN is rare in pregnancy. Active vasculitis poses risks to both mother (hypertension, renal failure) and fetus (fetal growth restriction).
• Management: Systemic GC are relatively safe. Cyclophosphamide is teratogenic and absolutely contraindicated. Azathioprine may be used for maintenance, and calcineurin inhibitors (e.g., tacrolimus) are alternatives.

Comorbidities

• HBV Infection: Requires antiviral therapy and PLEX, minimizing immunosuppression (as detailed above).
• Renal Insufficiency: Requires adjustment of CYC and careful monitoring of nephrotoxic drugs.

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Clinical Pearls

Diagnostic

• ANCA Negativity is Key: If ANCA is strongly positive, the diagnosis is likely an ANCA-associated vasculitis (which responds differently to treatment).
• The "Nodosa" is on Angiography: Do not wait for subcutaneous nodules to appear; the characteristic microaneurysms seen on abdominal angiography in the renal, hepatic, or mesenteric arteries are diagnostic evidence.
• Mononeuritis Multiplex: If this is the dominant feature, PAN is high on the differential.

Treatment

• Do Not Use Cyclophosphamide Indiscriminately in HBV: Always wait for HBV serology. Treating HBV-associated PAN with CYC without antivirals can lead to fulminant HBV reactivation and liver failure.
• Maintain Steroids During CYC Dosing: Steroids are necessary to suppress inflammation, especially during the intermittent pulse infusions of CYC.

Pitfalls

• Misdiagnosing as Essential Hypertension: Severe, new-onset, refractory hypertension in a middle-aged patient with systemic symptoms should prompt investigation for renovascular vasculitis (PAN).
• Missing GI Involvement: Vague chronic abdominal pain that escalates to perforation is an easy complication to miss. Maintain a high index of suspicion.

Recent Updates

Guidelines

• European League Against Rheumatism (EULAR): Contemporary guidelines emphasize risk stratification (using FFS) to tailor immunosuppression intensity. They strongly endorse the divergent treatment strategy for HBV-associated PAN (antiviral + PLEX preferred over CYC).

Evidence

• There is increasing evidence supporting the use of Rituximab (similar to its role in AAV) for induction and maintenance in idiopathic PAN, particularly in relapsing or refractory cases, offering a non-CYC alternative. However, it is not yet considered first-line induction therapy due to limited specific trial data compared to CYC.

Controversies

• Role of Routine Angiography: While historically definitive, the advent of biopsy of accessible symptomatic tissues and less invasive CTA/MRA means the routine use of catheter-based DSA is debated, especially given its associated risks.
• Optimal Duration of Maintenance Therapy: The exact duration of AZA/MTX maintenance (typically 12–18 months after remission) is still empirical, relying partly on AAV data.

Key References

Guidelines

• EULAR/ERA-EDTA Recommendations: Management of primary systemic vasculitides, focusing on risk stratification and treatment algorithms.

Studies

• The French Vasculitis Study Group (FVSG) Trials: Landmark studies establishing the efficacy and dosing of cyclophosphamide and the use of the FFS in vasculitis.

Reviews

• Comprehensive reviews in Nature Reviews Rheumatology and Rheumatic Disease Clinics of North America on the diagnosis and differential diagnosis of ANCA-negative vasculitides.