Xanthogranulomatous Pyelonephritis Presenting as a Psoas Abscess.

Xanthogranulomatous pyelonephritis (XGP) is a rare form of severe pyelonephritis. It is characterized by progressive parenchymal destruction caused by chronic urinary tract obstruction and infection, typically resulting in a non-functioning enlarged kidney. Its presentation with a psoas abscess is infrequent, and only a few cases are described in the literature. Unlike the typical presenting symptoms of XGP, our patient presented classic symptoms of lumbago. Once the diagnosis was established, antibiotics were given and a nephrectomy was performed. Unfortunately, after the surgery, the patient developed mild monoparesis on the right lower limb with decreased knee extension muscle strength and needed a walking stick for support. Nonetheless, a delayed diagnosis could have been fatal.