Assessment of the Rate of Decrease in Serum IgG4 Level of Autoimmune Pancreatitis Patients in Response to Initial Steroid Therapy as a Predictor of Subsequent Relapse

OBJECTIVES: Autoimmune pancreatitis (AIP) responds well to steroid therapy but frequently relapses after discontinuing the steroid. It is difficult to know which cases are most likely to relapse. The aim of this study was to investigate the relation between the rate of decrease in serum IgG4 level after initial steroid therapy and a relapse. METHODS: The subjects were 47 AIP patients who received steroid therapy. We calculated the difference between their serum IgG4 levels before and 2 months after the start of therapy, and their rate of decrease in serum IgG4 level after treatment (Δ') by dividing the difference between the 2 values by the number of days between them. RESULTS: The rates of decrease were significantly higher in the nonrelapse groups than in the relapse groups. A receiver operating characteristic curve showed that the area under the curve for the Δ' value was 0.781, and that at the Δ' cutoff value of 10.7, the sensitivity and the specificity of the Δ' value for discriminating between the 2 groups were 0.846 and 0.632, respectively. CONCLUSIONS: Our data suggest that the rate of decrease in serum IgG4 level may be a useful predictor of a relapse of AIP after steroid therapy.