Fever of unknown origin in a very old patient: beware of the kidney!

ANCA-associated vasculitis affects more than 20 per million of the population per year and prevails in the elderly. Renal involvement, either isolated or in the context of systemic vasculitis, is common. We report the case of an 86-year-old patient who presented with a histologically proven renal limited vasculitis and with fever and fatigue but with normal renal function and urine analysis. Serum creatinine increased and microscopic hematuria became evident only 3 weeks after symptoms onset, whereas ANCA positivity was the only early key to the diagnosis. This case shows that in the elderly an ANCA-related pauci-immune glomerulonephritis in its earliest stages should be suspected in the presence of a fever of unknown origin even if serum and urine analyses are normal.