Comparison of two subsets of Chinese patients with retroperitoneal fibrosis in terms of IgG4 immunohistochemical staining.

Objective. To identify clinical and pathological differences between IgG4-related retroperitoneal fibrosis (IgG4-RPF) and idiopathic RPF (iRPF) in a Chinese population. Method. Clinical and pathological data of 50 RPF patients from 2006 to 2016 were retrospectively analysed. The presence of at least one characteristic histopathological feature, >30 IgG4(+) plasma cells per high power field, and an IgG4(+)/IgG(+) plasma cells ratio cutoff of >40% were used to define IgG4-RPF. Results. Patients with IgG4-RPF were significantly more likely to have pain (94.1 vs 68.8%, P=0.048), elevated serum IgE concentration (166.1 vs 40.2 IU/ml, P=0.029) and tissue eosinophilia (47.1 vs 12.5%, P= 0.018), compared with patients with iRPF. In the IgG4-RPF subgroup, patients with tissue eosinophilia demonstrated higher levels of CRP (4.3 vs 1.9 mg/di, P= 0.027) and ESR (62.1 vs 22.8 mm/h, P = 0.001). Among the 50 patients with RPF, the average number of tissue IgG4 plasma cells was positively correlated with the number of tissue eosinophils (r= 0.37, P = 0.009). Moreover, serum IgG4 concentration and serum IgE concentration showed positive correlation (r= 0.834, P = 0.000). Conclusion. The distinct serological and histopathological features of Chinese patients with IgG4-RPF were elevated serum IgE concentration and tissue eosinophilia, which potentially can aid and support the diagnosis. As serum IgG4 concentration may be normal in patients with IgG4-RPF, serum IgE may represent a useful serological marker in distinguishing IgG4-RPF from iRPF.