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Stem
A 50-year-old man presents with six weeks of fever, fatigue and 7 kg weight loss. Three weeks ago he developed a painful right foot drop, and one week ago a left wrist drop. He now has post-prandial central abdominal pain that has made him afraid to eat. Examination reveals livedo reticularis over the lower limbs, several tender subcutaneous nodules on the legs, weak ankle and wrist dorsiflexion, and a blood pressure of 170/102. His urinalysis shows no protein and no blood. ANCA is negative. Bloods show ESR 96 mm/h, creatinine 165 micromol/L (eGFR 42), and HBsAg positive.
Questions
a) What is the most likely diagnosis, and which two features in the stem most strongly distinguish it from the ANCA-associated vasculitides? (2 marks)
Model answer: Polyarteritis nodosa (PAN) (1 mark) — a necrotising vasculitis of MEDIUM muscular arteries. The two discriminating features are the BLAND URINALYSIS (no glomerulonephritis) and the NEGATIVE ANCA, together with medium-vessel disease (mononeuritis multiplex, livedo, nodules, renovascular hypertension) (1 mark). PAN spares the glomerulus and the lung, and is ANCA-negative — unlike microscopic polyangiitis, which is small-vessel, ANCA-positive and causes pauci-immune glomerulonephritis and pulmonary capillaritis.
b) Outline the investigations you would perform to confirm the diagnosis, naming the radiological hallmark. (3 marks)
Model answer: CT, MR or conventional mesenteric/renal ANGIOGRAPHY — the radiological hallmark is MICROANEURYSMS and a 'beaded' irregular outline of the renal, mesenteric and hepatic arteries (1). Tissue biopsy of an involved organ (sural nerve and muscle, skin nodule, gut, or testis) showing transmural medium-vessel vasculitis with fibrinoid necrosis and disruption of the internal elastic lamina (1). Bloods — ESR/CRP raised, ANCA negative, bland urinalysis (no glomerulonephritis), and HBV serology (HBsAg, anti-HBc) plus HCV/HIV; complement low and cryoglobulins in HBV-associated PAN (1).
c) The patient is HBsAg positive. Describe how this changes the treatment, naming the three components of the regimen and the rationale. (3 marks)
Model answer: Hepatitis-B-associated PAN is treated with ANTIVIRAL THERAPY (entecavir or tenofovir) plus PLASMA EXCHANGE (to remove circulating HBV-antigen immune complexes) plus a SHORT course of corticosteroids (2 marks). The rationale is that the vasculitis is driven by circulating HBV-antigen immune complexes (hence low complement and cryoglobulins), so the goal is HBV CLEARANCE, not long-term immunosuppression — unlike idiopathic PAN, which is treated with high-dose steroids plus cyclophosphamide for severe disease (1 mark). HBV-PAN is usually monophasic and rarely relapses once HBV is controlled.
d) Name three serious complications of polyarteritis nodosa and the single most important long-term consideration in this patient. (2 marks)
Model answer: Any three of: residual mononeuritis multiplex (foot/wrist drop), mesenteric ischaemia or gut perforation, renovascular hypertension and chronic kidney disease (NOT glomerulonephritis), coronary arteritis and cardiac failure, stroke or cerebral vasculitis, or microaneurysm rupture with haemorrhage (1 mark). The most important long-term consideration is clearance and surveillance of hepatitis B (with hepatology input), combined with long-term cardiovascular and renal surveillance, as PAN leaves patients with renovascular hypertension and an elevated cardiovascular risk (1 mark).