The aim of this study is to establish a nation-wide cohort study of idiopathic retroperitoneal fibrosis (IRPF) in China.

Methods: All the patients fulfilling diagnostic criteria of IRPF would be enrolled from multi-centers around China. A online database system has been established.

Endpoints: The primary endpoint is to investigate the clinical manifestations of Chinese IRPF patients; the secondary endpoints including the demographic features,laboratory characteristics, immunological tests, imaging and pathological features, in addition, the treatment and prognosis of the disease.

This is a multicenter registry study of IRPF patients. Newly diagnosed IRPF patients will be recruited from all over the China. Inclusion criteria: patients with newly diagnosed IRPF will be recruited. Exclusion criteria: patients with secondary forms of retroperitoneal fibrosis or malignancy are excluded.

The data will be uploaded through the platform of Chinese Rheumatology Information Platform. Demographic data, initial symptoms, disease duration, history of allergy, and physical examination, organ involvements, laboratory findings, radiological and pathological results, as well as treatment, side effects will be recorded.

This study was approved by the Medical Ethics Committee of PUMCH (Beijing, China). All patients will sign informed consent.

Statistical Analysis: All parameters are described in the standard summary statistics, including mean, standard deviation, minimum, and maximum. All statistical analyses will be performed by SPSS.

Endpoints: The primary endpoint is to investigate the organ involvements of Chinese IRPF patients. The secondary endpoints include the demographic features,laboratory characteristics, immunological tests, imaging and pathological features, in addition, the treatment and prognosis of the disease.

Inclusion Criteria:

• Conforming to the diagnostic criteria of IRPF;Definite IRPF must have the following characteristics: (1) The typical finding of Imaging shows retroperitoneal mass, surrounding the abdominal aorta and iliac arteries, with encasement of ureters and/or organ dysfunction; (2) Exclusion of disease progression after standard glucocorticoid treatment; and (3) histopathological findings shows a fibrous tissue with signs of chronic inflammation. The inflammatory component is comprised of lymphocytes, plasma cells and macrophages. Neutrophils and granulomas are rare findings. Possible IRPF required (1) and (2), but without histopathological examination.

Exclusion Criteria:

• None of them met the criteria for other autoimmune diseases. None had malignant disease. Secondary forms of RPF related to drugs, infections, malignancies, Erdheim-Chester disease and IgG4-RD, need to be excluded.

IRPF patients around China.