Polyarteritis Nodosa
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Direct answer
Polyarteritis nodosa (PAN) is a necrotising vasculitis of medium and small muscular arteries that spares the glomerulus and the lungs, a pairing that separates it from the ANCA-associated vasculitides in a single examination line. Classically it presents with fever, weight loss, a painful nodular skin rash with livedo racemosa, mononeuritis multiplex, testicular pain, and abdominal angina, with or without hepatitis B infection. Diagnosis rests on biopsy of an involved organ, such as skin, nerve or muscle, or on angiography showing microaneurysms and stenoses of renal, hepic or mesenteric branches; treatment is glucocorticoids plus cyclophosphamide for severe disease, while hepatitis B-related PAN is treated with antiviral therapy with short-course steroids and plasma exchange.
What you must remember
- PAN is characteristically ANCA-negative; a positive ANCA in this picture points instead to microscopic polyangiitis or eosinophilic granulomatosis with polyangiitis.
- Renal involvement is renovascular, producing hypertension, renal infarction and non-aneurysmal ischaemia, but not glomerulonephritis or active urinary sediment.
- Lung is spared in PAN; pulmonary involvement moves the diagnosis to the ANCA-associated group.
- Mononeuritis multiplex, sequential painful asymmetric nerve deficits from vasa nervorum vasculitis, is the neurologic hallmark; foot drop and wrist drop appear in the same patient.
- Hepatitis B association is historically important, seen in a subset classically within a year of infection, so every PAN workup includes hepatitis B surface antigen.
- Angiography shows saccular microaneurysms and irregular stenoses of mesenteric and renal branches, the cobwebs of the mesenteric circulation.
- Cutaneous limited PAN presents with nodules, livedo and ulceration without visceral disease, and has a good prognosis.
A worked case from rash to diagnosis
A 46-year-old man has six weeks of fever, 7 kg weight loss, a painful right foot drop, tender red nodules over the legs, a livedo pattern on the calves and post-prandial abdominal pain. Blood pressure is 160/100 mmHg; urine shows no protein or sediment; ANCA is negative.
Step one: confirm the neuropathy. Nerve conduction studies show an asymmetric axonal sensorimotor neuropathy; combined nerve and muscle biopsy of the superficial peroneal nerve with peroneus brevis is the highest-yield tissue diagnosis in a patient with foot drop.
Step two: define visceral involvement. Renal angiography demonstrates microaneurysms in renal and mesenteric branches; serum creatinine is mildly raised with a bland urine; CT abdomen may show bowel wall thickening or infarcts. Testicular examination and ultrasound matter, as testicular pain distinguishes PAN clinically from other vasculitides.
Step three: screen for drivers. Hepatitis B surface antigen and DNA, hepatitis C and HIV serology; hepatitis B-associated PAN gets entecavir or tenofovir, a short course of steroids and plasma exchange, an antiviral-first strategy that clears antigenaemia and improves survival.
Step four: treat by severity. Non-organ-threatening disease may manage with high-dose steroids alone; poor-prognosis disease, scored by the five-factor score items of renal impairment, proteinuria, gastrointestinal ischaemia, cardiomyopathy and central nervous involvement, adds cyclophosphamide followed by maintenance azathioprine or methotrexate.
Step five: monitor and prevent damage. Control blood pressure aggressively to protect the ischaemic kidneys, follow the neuropathy with physiotherapy and splints, and surveil for relapse, which is lower in PAN than in the ANCA-associated diseases once remission is achieved.
Where the exam tries to catch you
The classic discriminator is the kidney-lung pairing. Glomerulonephritis with haemoptysis is microscopic polyangiitis or granulomatosis with polyangiitis; hypertension with a bland urine, abdominal pain and lung fields that are clean is PAN. The second favourite is Kawasaki disease, which is histologically PAN-like and produces coronary aneurysms in children, a deliberate distractor when the question mentions a five-year-old with coronary dilation. Also beware the cocaine-levamisole vasculopathy mimics and, in India, hepatitis B screening is not optional: missing it commits the patient to needless cyclophosphamide while the viral driver smoulders.
Frequently asked questions
Is PAN associated with ANCA?
No; PAN is characteristically ANCA-negative, unlike microscopic polyangiitis and granulomatosis with polyangiitis.
Which viral infection drives a subset of PAN?
Hepatitis B, treated with antivirals plus short-course steroids and plasma exchange rather than prolonged immunosuppression.
What is the classic neuropathy of PAN?
Mononeuritis multiplex, asymmetric axonal neuropathy from vasa nervorum occlusion, such as simultaneous foot drop and wrist drop.
What does mesenteric angiography show?
Saccular microaneurysms with irregular stenoses of medium-sized branches, the cobweb appearance.
Which score estimates prognosis?
The five-factor score, awarding points for renal impairment, proteinuria, gastrointestinal involvement, cardiomyopathy and CNS disease, guiding the addition of cyclophosphamide.
Which organs are characteristically spared?
The lungs and the glomeruli, a combination that is nearly diagnostic in exam stems.