BACKGROUND: Idiopathic retroperitoneal fibrosis is characterized by the development of inflammatory infiltrates with marked fibrosis along the large retroperitoneal vessels. Rituximab in combination with glucocorticoids constitute an effective therapy, but the responses are not long-lasting. In other similar situations, addition of cyclophosphamide to the combination achieved longer and deeper responses. This was the reason to use the triple combination in this case. CASE: A 56-year-old man came with four weeks lasting abdominal pain with CT finding of retroperitoneal fibrosis with unilateral ureteral occlusion. Biopsy confirmed retroperitoneal fibrosis with histological findings of IgG4-associated disease. Treatment with prednizone was poorly tolerated. Therefore, the patient was switched to the combination of rituximab 375 mg/m2 on day 1, cyclophosphamide 300 mg/m2 in infusion in days 1 and 15, plus dexamethasone 20 mg in infusion on days 1 and 15, repeated in a 28-day cycle. RESULTS: Fluorodeoxyglucose (FDG) positron emission tomography (PET/CT) examination after 4 months of treatment showed a marked decrease in FDG accumulation and complete disappearance of the fibrotic mass. After 8 months, the induction therapy was followed by maintenance therapy with rituximab 1,000 mg plus dexamethasone 20 mg in 6-month intervals. Control PET/MR examination after 3 years is consistent with complete remission. The number of circulating plasmablasts correlated with the disease activity. CONCLUSION: Treatment of retroperitoneal fibrosis with the tripple combination of rituximab, cyclophosphamide and dexamethasone achieved a very rapid disappearance of pathological FDG accumulation and fibrotic retroperitoneal mass, with complete disappearance achieved after 4 months of treatment. After 3 years of maitenance therapy, the diesease is still in complete remission on PET/MR examination. We suggest to continue the maintenance therapy with rituximab because of some increase in the number of circulating plasmablasts after prolongation of the intervals between rituximab administration.

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