The histological diagnosis of IgG4-related disease on small biopsies: challenges and pitfalls.

Patients with a presumptive diagnosis of IgG4-RD but lacking the characteristic pathological features of this disease appear to be clinically similar to those who meet the current pathological criteria. An elevated IgG4/total IgG ratio is the most sensitive pathological feature, and ISH provides a robust quantification platform. We recommend evaluating tumefactive lymphoplasmacytic infiltrates with an increased IgG4/IgG ratio, regardless of histological features, for IgG4-RD.