Medium vessel vasculitis · KIMS Secunderabad
Polyarteritis Nodosa — Medium Vessel Vasculitis and Its Renal Consequences
Polyarteritis nodosa (PAN) is a necrotising vasculitis affecting medium-sized arteries — particularly the renal arteries and their branches, the mesenteric arteries, the coronary arteries, and the peripheral nerve arteries. Unlike the small-vessel vasculitides (ANCA-associated vasculitis — ANCA-AAV, which targets arterioles and glomerular capillaries), PAN targets medium-sized muscular arteries and does not cause glomerulonephritis. PAN is ANCA-negative — this serological distinction from ANCA-AAV (which is ANCA-positive) is the critical diagnostic test.
In the kidney, PAN causes renal artery aneurysms, arterial occlusion, and renal infarction — not glomerulonephritis. The clinical consequences are renovascular hypertension (from renal artery lesions activating the RAAS), haematuria (from infarction or rupture of renal artery aneurysms), and AKI or progressive CKD from ischaemic nephron loss. In India, an important secondary cause of PAN is hepatitis B virus (HBV) infection — HBsAg-positive PAN accounts for approximately 30 to 35% of PAN cases globally, and HBV is endemic in India.
Clinical features — multisystem vasculitis
Organ-system manifestations of polyarteritis nodosa
Systemic features — fever, weight loss, fatigue, malaise — the hallmarks of active vasculitis.
Renal manifestations — hypertension (often severe, from renal artery involvement activating the RAAS), flank pain (from renal infarction), haematuria (from infarction or aneurysm rupture), and gradually declining eGFR from ischaemic nephron loss. Nephrotic syndrome does not occur in PAN — it is a medium vessel disease that does not cause glomerulonephritis.
Peripheral neuropathy — mononeuritis multiplex (asymmetric involvement of multiple named peripheral nerves — foot drop, wrist drop, patchy sensory loss in different nerve distributions) from vasculitis of the vasa nervorum. One of the most characteristic clinical features of PAN.
Gastrointestinal — abdominal pain, nausea, and intestinal ischaemia from mesenteric arteritis. Bowel infarction is a life-threatening complication.
Skin — livedo reticularis (lacy purplish skin pattern), subcutaneous nodules along the course of affected arteries, skin ulcers.
Testicular pain — from testicular artery involvement (vasculitis of the testicular arteries causes orchitis-like pain without infection).
Diagnosis at KIMS
ANCA (ANCA-MPO and ANCA-PR3)
Negative in PAN. The most important initial test. A negative ANCA in a patient with multisystem vasculitis and renal involvement points away from ANCA-AAV and toward PAN, polyarteritis-like vasculitis (e.g. HBV-PAN), or other medium vessel vasculitis.
HBsAg, HBV DNA, HCV antibody
Essential — identifies HBV-associated PAN (which has different treatment implications from idiopathic PAN). HBV PAN is treated with antiviral therapy (tenofovir) + plasma exchange + short-course steroids, followed by steroid withdrawal (steroids are tapered rapidly because they promote HBV replication). Idiopathic PAN is treated with standard steroids + cyclophosphamide.
CT angiography or conventional angiography
The diagnostic investigation of choice for PAN. Shows the characteristic findings: microaneurysms of the medium-sized arteries (renal, mesenteric, hepatic), segmental stenoses alternating with areas of dilatation ('beads on a string' appearance), renal infarcts (wedge-shaped perfusion defects in the renal parenchyma). Angiography is required when CT angiography cannot fully characterise the small aneurysms.
Tissue biopsy — nerve, skin, or muscle
Histology shows necrotising inflammation of medium-sized arterial walls — fibrinoid necrosis of the media with neutrophilic and eosinophilic infiltration. Renal biopsy in PAN shows ischaemic changes rather than glomerulonephritis — it is not the primary diagnostic tool for PAN.
Treatment
Idiopathic PAN
High-dose prednisolone (1 mg/kg/day) combined with cyclophosphamide (oral or IV pulse) for induction remission. Five-factor score (FFS — a validated prognostic scoring system) guides treatment intensity: FFS above 1 (severe disease with GI, cardiac, or renal involvement) warrants cyclophosphamide addition. Remission maintenance with azathioprine after 3 to 6 months of cyclophosphamide. Rituximab for refractory or relapsing PAN.
HBV-associated PAN
Antiviral therapy (tenofovir or entecavir) + plasma exchange (to remove immune complexes) + short course prednisolone (tapered over 2 to 4 weeks). Long-term immunosuppression with cyclophosphamide is avoided because it promotes viral replication. HBeAg seroconversion (development of anti-HBe antibody, indicating viral suppression) correlates with remission of the vasculitis.
Book a Vasculitis Assessment at KIMS
Frequently Asked Questions — Polyarteritis Nodosa
No — PAN and ANCA-associated vasculitis (ANCA-AAV) are completely different conditions, though both are necrotising vasculitides. The most important distinction: PAN targets medium-sized arteries (renal arteries and their branches) and is ANCA-negative. ANCA-AAV (granulomatosis with polyangiitis, microscopic polyangiitis, eosinophilic GPA) targets small vessels (arterioles, capillaries, venules) and is ANCA-positive (MPO-ANCA or PR3-ANCA). In the kidney, PAN causes renal artery lesions and infarction; ANCA-AAV causes pauci-immune glomerulonephritis. The biopsy appearances are completely different: necrotising arteritis in PAN vs crescentic pauci-immune GN in ANCA-AAV.
Yes — HBV infection is an important cause of PAN, accounting for approximately 30 to 35% of all PAN cases. HBV surface antigen (HBsAg) and HBV core antigen form immune complexes that deposit in medium vessel walls, triggering the necrotising inflammatory response. HBV-related PAN has different treatment implications: antiviral therapy (tenofovir) is the primary treatment, plasma exchange removes the causative immune complexes, and steroids are used briefly and tapered rapidly to avoid promoting HBV replication. In India, where HBV prevalence is high (approximately 3 to 4% of the population are HBsAg carriers), HBV testing is mandatory in all PAN patients before treatment is started.
Microaneurysms are small outpouchings or dilations of the arterial wall at sites where the vasculitic process has weakened the vessel wall. In PAN, microaneurysms form predominantly in the renal, mesenteric, and hepatic arterial beds. They are visible on CT angiography or conventional angiography as small outpouchings of the vessel — the 'beads on a string' appearance when alternating with areas of stenosis. Microaneurysms may rupture — causing acute haemorrhage (renal or abdominal), which is a life-threatening complication. Spontaneous rupture of a renal microaneurysm in PAN can present with acute flank pain and haemodynamic shock from retroperitoneal haemorrhage.
The degree of permanent kidney damage in PAN depends on the extent and duration of renal artery involvement before treatment is started. Each episode of renal infarction destroys the corresponding nephrons permanently — the infarct appears as a cortical scar on subsequent imaging. Progressive microinfarction from uncontrolled PAN causes cumulative nephron loss and declining eGFR. Aggressive immunosuppression (and antiviral therapy in HBV-PAN) initiated early prevents further infarction and stabilises kidney function — but existing infarcts are not reversible. Renovascular hypertension from renal artery stenosis in PAN may require angioplasty in selected cases.
KIMS Secunderabad — Dr. Aswini Dutt T (glomerular disease and vasculitis subspecialty), ANCA testing, HBsAg and HBV DNA, CT angiography for microaneurysm detection, tissue biopsy (nerve and skin), prednisolone + cyclophosphamide for idiopathic PAN, tenofovir + plasma exchange for HBV-PAN, rituximab for refractory cases, renovascular hypertension management. NABH and NABL accredited. Call 040-4488-5000.