Chronic Tubulo-interstitial Pyelonephritis with Retroperitoneal Fibrosis.

A large proportion of patients with retroperitoneal fibrosis (RPF) have been labelled as having idiopathic RPF historically. Recent reports of a subset of these patients having a fibro-inflammatory condition with characteristic histology and good response to therapy has helped in renewed understanding of an old disease. A 40 year old man presented with vague abdominal discomfort of 5 months duration. Ultrasound examination revealed soft tissue thickening with calcification over lower abdominal aorta. CT scan characterized the lesion as a retroperitoneal mass encasing the aorta with an associated lesion in upper pole of left kidney. A laparoscopic surgery and biopsy of the mass lesions were performed. It was reported as chronic tubulo-interstitial disease with retroperitoneal fibrosis. In the post-operative period, patient developed fever with weight loss. An 18F-FDG PET-CT done revealed FDG-avid retroperitoneal mass lesion. Serum IgG-4 levels were elevated and review of biopsy revealed features of IgG4 related disease. Patient had good response to treatment with steroids and azathioprine.