A case of Serratia granuloma in the soft tissue around the left kidney: a role of PTHrP in the formation of Serratia granuloma

Serratia marcescens is an ubiquitous, saprophytic gram-negative bacillus that is associated with infections such as bacteremia, pneumonia and osteomyelitis. However, it has not been known to form granulomas. A 72-year-old man with a history of tricuspidal insufficiency, mitral insufficiency and ureterolithiasis presented with lumbago on the left side. He was admitted to our hospital, where abscess formation in the subcapsular space and perirenal fat space of the left kidney, and left renal calculi were identified by computed tomography of the abdomen. As infection and/or a tumor were suspected, nephrectomy was performed. The histopathological findings in the resected kidney indicated severe infiltration by inflammatory cells with lymphoid follicles in the interstitium, and the proliferation of mesangial cells and matrix in glomerulus. Furthermore, giant cell granulomas were observed in the soft tissue around the kidney. As an aerobic culture of the abscess from the granulomas only produced Serratia marcescens, these granulomas were diagnosed as Serratia marcescens granulomas. In addition, expressions of PTHrP and PTH/PTHrP-receptor were observed in the giant cells in Serratia granuloma, which suggested that PTHrP might be involved in giant cell formation in Serratia granuloma by autocrine and/or paracrine mechanisms.