Case Presentation: A previously healthy 23-year-old male training for an ultramarathon presented with acute-onset severe back pain and subacute B symptoms (fever, night sweats). CT revealed retroperitoneal lymphadenopathy, which prompted urgent transfer to an academic medical center for further evaluation. He was found to have thrombosis of the IVC and left internal, left external, and right internal iliac veins, as well as numerous pulmonary emboli. Concern for malignant etiology was high, and broad evaluation for malignancy, infection, and autoimmune disease was largely negative, with fibrosis demonstrated on surgical biopsy and no hypermetabolic activity on inpatient PET. With malignancy excluded, idiopathic retroperitoneal fibrosis (IRF) was diagnosed. He was started on prednisone, received two doses of rituximab, underwent IVC and iliac vein thrombectomy, and was discharged with rheumatology and IR follow-up for steroid taper and outpatient anticoagulation. He presented one month later with persistent bilateral lower extremity edema and ultimately underwent repeat thrombectomy of the left femoral vein with bilateral iliac stent placement. He continues to gradually taper prednisone.
Discussion: IRF involves immune-mediated fibroinflammatory tissue formation in the retroperitoneum, typically encasing the aorta and iliac arteries and causing ureteral obstruction and renal failure.(1,2) Chronic inflammation from various immune cells drives fibroblast activation and collagen deposition, with genetic, environmental, and cytokine factors contributing to disease susceptibility.(1,2) As this patient initially presented with nonspecific symptoms (back pain and B symptoms), the differential was quite broad, including malignant, infectious, inflammatory, and autoimmune causes. He underwent an extensive work-up as a result, with IRF ultimately being a diagnosis of exclusion. This diagnosis was suggested by surgical biopsy showing fibrosis with inflammatory infiltrate, although concern for malignancy was so high that an inpatient PET was obtained in order to fully rule out malignancy.(3)IRF management begins with oral glucocorticoids, followed by a gradual taper over several months. While vascular complications in association with IRF are rare, they have been reported, and in cases such as this one where claudication and DVT occur, thrombectomy or vascular stenting may be utilized.(6) In the case of IVC obstruction, anticoagulation is needed in addition to immunosuppression.
Conclusions: IRF presents with a multisystem clinical phenotype, rarely manifesting with thrombotic complications necessitating thrombectomy and vascular stenting. Current treatments focus on slowing progression with glucocorticoids and vascular or surgical intervention in the case of obstruction. Our case highlights how IRF can masquerade as malignancy with overlapping findings (B symptoms, lymphadenopathy, hypercoagulability) and can ultimately respond to immunosuppression, anticoagulation, and vascular intervention.