Delayed eculizumab therapy guided by markedly elevated soluble C5b-9 in a child with dialysis-requiring acute poststreptococcal glomerulonephritis: a case report.

Eculizumab, a monoclonal antibody targeting complement C5, has been shown to be effective when administered within 2-4 days of disease onset in children with severe acute poststreptococcal glomerulonephritis (APSGN). However, since APSGN typically follows a self-limited clinical course in most patients, the optimal timing and latest feasible time window for eculizumab initiation in APSGN remain undefined. A 9-year-old girl presented with gross haematuria, oliguria, and renal dysfunction 9 days after the onset of vomiting and abdominal pain. Laboratory tests showed a positive anti-streptolysin O titre, decreased serum complement C3 levels, massive proteinuria, and stage 3 acute kidney injury. Following high-dose methylprednisolone and continuous renal replacement therapy, her serum C3 levels recovered to normal range, yet oliguria and renal impairment persisted two weeks after disease onset. Since serum complement membrane attack complex (C5b-9) remained substantially elevated, eculizumab was initiated at a delayed time point compared with previous reports, yielding a rapid improvement in renal function. Kidney biopsy performed post-treatment with eculizumab revealed focal proliferative glomerulonephritis, accompanied by acute tubular injury. At the 6-month follow-up, except for haematuria detected by dipstick urinalysis, the patient had normal renal function, serum complement C3 levels and negative urinary protein. No severe adverse events occurred. We present a case of APSGN with persistent renal dysfunction and excessive complement activation 2 weeks after glucocorticoid therapy, who achieved substantial clinical remission upon eculizumab administration. Our observation suggests eculizumab may be an effective rescue intervention for persistent renal dysfunction in severe APSGN driven by excessive complement activation.