Renal Pelvic and Periureter Masses in Cutaneous and Systemic Plasmacytosis

We report a case of cutaneous and systemic plasmacytosis (CSP), with unusually large bilateral renal pelvic and periureteral masses, accompanied by severe renal dysfunction. A 53-year-old man with disseminated reddish-brown plaques developed progressive renal failure over 3 years. Laboratory tests revealed polyclonal hypergammaglobulinemia; imaging showed renal masses and lymphadenopathy. Skin and lymph node biopsies confirmed plasma cell infiltration. After excluding other differential diagnoses, the renal involvement was considered to share a common cause with other lesions, and CSP was diagnosed. Subsequent glucocorticoid therapy improved renal function, cutaneous lesions, and periaortic lymphadenopathy, highlighting its efficacy for CSP-related renal disease.