Idiopathic retroperitoneal fibrosis (IRF) is a rare disease, characterized by the presence of fibro-inflammatory tissue that surrounds abdominal aorta and often entraps ureters. Classical approach to medical treatment is glucocorticoid monotherapy, but this may have several side effects. Because of its anti-inflammatory and anti-fibroblastic effects tamoxifen is safely used in treatment of IRF. As validated, FDG-PET/CT is used in the assessment of the metabolic activity of this pathology, in order to evaluate the response to therapy.
A 59-year-old man, suffering from IRF was referred to our institution for regular metabolic evaluations of the disease with FDG-PET/CT from 2011 (the last two PET in September 2012 and December 2013). He has been treated from 2009 to December 2013 with standard medical approach (corticosteroids), showing no significant clinic and metabolic response to therapy.
Considering the persistently elevated metabolic activity of disease and poor clinical response, clinicians shifted to off-label use of tamoxifen (40mg/day). Restaging FDG-PET was made after 7 months from beginning of this therapy (august 2014).
Every FDG-PET acquisition has been made with a Philips Gemini scanner, 1 hour after the injection of 200 Mbq of FDG.
Presence of FDG uptake in the retroperitoneal mass was visually evaluated and tracer uptake was semi-quantitatively assessed in therms of SUVmax, calculated after positioning of a region of interest on the retroperitoneal mass, excluding renal pelvis, in order to avoid physiological urinary activity. Visual assessment showed reduction in extent and intensity of FDG distribution in the lesion area after the therapy shift, confirming semi quantitative data (PET Sep. 2012 SUVmax: 7,1; PET Dec 2013 SUVmax: 7,4; PET Aug 2014 SUVmax: 4,4).
According to the decrease in metabolic activity, also RCP (reactive C-protein) and ESV (erithrosedimentation velocity) decreased (Nov. ’13 ESV: 17 mm/h, RCP: 21mg/l; May ’14 ESV: 13mm/h, RCP: 7,1mg/l).
IRF is a rare pathology, with little literature, and this is, to our knowledge, the first case report showing a positive metabolic impact of tamoxifen therapy on IRF, confirming tamoxifen anti-inflammatory effects also in IRF.
FDG-PET/CT has proven to be a useful tool in the decision-making process for the IRF patients, when following the evolution of the pathology and when choosing the most effective therapy.

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