Acute glomerulonephritis

Definition — the acute nephritic syndrome. Abrupt onset of haematuria with dysmorphic red cells and red cell casts, proteinuria (usually sub-nephrotic), hypertension, oedema and oliguria, with a rising creatinine. When crescents involve more than 50% of glomeruli and function is lost over days to weeks, it is termed rapidly progressive glomerulonephritis (RPGN).

Age-specific epidemiology — this is a disease of the old. Crescentic glomerulonephritis reaches its greatest incidence between 60 and 79 years and presents as rapidly progressive acute renal failure. Renal vasculitis is probably the most common primary cause of renal failure in older adults. Post-streptococcal and other post-infectious glomerulonephritis are more frequent in older than in younger patients — in the elderly typically staphylococcal-associated or endocarditis-related rather than streptococcal.

Classification by immunofluorescence — the framework the examiner wants. (a) Pauci-immune — ANCA-associated vasculitis (granulomatosis with polyangiitis, microscopic polyangiitis); commonest pattern in the elderly. (b) Immune-complex (granular) — post-infectious, IgA nephropathy and Henoch–Schönlein purpura, lupus nephritis, cryoglobulinaemia (hepatitis C), membranoproliferative GN. (c) Linear — anti-glomerular basement membrane disease, which has a second incidence peak in older adults.

Presentation in old age is non-specific and easily missed. Malaise, weight loss, low-grade fever, arthralgia, anorexia, normocytic anaemia, cough or haemoptysis (pulmonary–renal syndrome), purpuric rash, mononeuritis multiplex, or scleritis. The renal failure is often discovered incidentally on routine bloods and is at real risk of being dismissed as "ageing", dehydration or prerenal AKI — losing treatable time in a condition where days matter.

Investigations. Urine microscopy for dysmorphic red cells and red cell casts is the single most useful bedside test. Then urine protein–creatinine ratio, creatinine, ANCA (MPO and PR3), anti-GBM, ANA and anti-dsDNA, C3 and C4, ASO titre, blood cultures and echocardiography if endocarditis is possible, hepatitis B and C serology, cryoglobulins, and chest imaging. Renal biopsy is the definitive investigation — its complications are no more frequent in older adults, though they are more serious when they occur.

Management. Treat the underlying cause. For crescentic and vasculitic disease, steroids and other immunosuppressive drugs such as cyclophosphamide can be used in older as in younger adults, although with special attention to their side effects; careful monitoring of therapy can minimise adverse effects in this population. Add plasma exchange for anti-GBM disease and for severe pulmonary haemorrhage. Supportive care: blood pressure control, salt and fluid restriction, loop diuretics, correction of hyperkalaemia, and dialysis where required. Post-infectious glomerulonephritis needs antibiotics and supportive care only, not immunosuppression.

KDIGO ANCA-Associated Vasculitis guidance — rituximab and steroid sparing, both particularly valuable in the elderly. For new-onset organ-threatening disease, induction is with glucocorticoids plus either rituximab or cyclophosphamide, with rituximab preferred in older adults and in anyone at risk of cyclophosphamide toxicity — infection, marrow suppression, malignancy and infertility. Rituximab is also preferred for maintenance of remission. Two further changes matter for geriatric practice: a reduced-dose glucocorticoid taper (PEXIVAS-style) achieves the same remission rates with significantly fewer serious infections; and the oral C5a receptor antagonist avacopan permits substantial steroid sparing — directly relevant in an older patient at risk of steroid-induced diabetes, osteoporosis, infection, delirium and myopathy. Prophylaxis against Pneumocystis jirovecii with co-trimoxazole is standard during induction.