Acute lumbago and sciatica as first symptoms of focal xanthogranulomatous pyelonephritis.

Xanthogranulomatous pyelonephritis (XGP) is a rare inflammatory disease of the kidney, presenting in a diffuse or focal form. The preoperative diagnosis of XGP is made only in 10% of the cases because neither the clinical nor the radiological presentation are specific and could be confused with renal tumors, thus deserving the name of 'great imitator'. We report a case of focal XGP in a middle-aged man presenting with acute lumbago and sciatica, an unusual clinical presentation.