Would you intensify therapy in IgG4 related disease based solely on a persistently significantly elevated IgG4 level when all disease manifestations and inflammatory markers have normalized?

While a perfect biomarker does not exist in IgG4-related disease (IgG4-RD), patients who have elevated serum IgG4 concentrations at baseline typically demonstrate a significant reduction of IgG4 concentrations after treatment and with improved disease activity. In patients treated with rituximab, one typically observes an initial rapid decline in serum IgG4 concentrations followed by a prolonged, much slower decline thereafter (Carruthers et al., PMID 25667206).

Not all patients achieve a normal IgG4 concentration; in fact, many patients continue to have persistent serum IgG4 elevations during clinical remission. However, it would be atypical for a patient with IgG4-RD to have improvement in disease activity after treatment without a corresp...