How do you approach management of a patient with a retroperitoneal soft tissue mass and elevated IgG4 level when tissue biopsy is not feasible?

The question of whether to biopsy in presumed retroperitoneal fibrosis is asked in almost every case. The reason for the biopsy is to primarily rule out other causes of retroperitoneal masses, such as lymphoma, infection, and other rare variants. The mildly elevated IgG4 is not very helpful due to the large number of causes for high IgG4 levels, such as allergic diseases. The CT scan can be helpful if the mass is homogeneous, does not elevate the aorta off the vertebrae, and is not invasive into...

I really prefer a biopsy if at all possible. I suppose you could look at it this way. What is the chance this is not IgG4 and/or cancer? Reasonable to think of rituxan if hepatitis and TB are negative after failing MTX or MMF (meaning scans show increased progression >6 months on DMARD). If concern for infection, then probably a biopsy is warranted prior to any immunosuppression therapy. You can hang on to whatever lab is positive: CRP/ESR, IgE, eosinophilia, IG panel, and IgG4 subclass, and get...