The Usefulness of Diffusion-Weighted MRI for Evaluating the Effects of Steroid Therapy for Autoimmune Pancreatitis and Differentiating it from Pancreatic Cancer

Abstract

Purpose: Autoimmune Pancreatitis (AIP) is a disease which is remarkably responsive to steroid therapy. The methods used to evaluate the effects of steroid therapy vary by hospital. In addition, there are many reports of cases difficult to distinguish from pancreatic cancer. Diffusion-weighted magnetic resonance imaging (DWI) is a non-invasive and quantitative evaluation that uses the apparent diffusion coefficient(ADC) values. This study revealed the usefulness of DWI for evaluating the effects of steroid therapy for AIP, and differentiating it from pancreatic cancer in our hospital. Methods: Four AIP patients underwent DWI before steroid therapy after one week and one month of treatment. We measured each ADC value and compared them. We also compared the ADC values of AIP patients to those of 30 pancreatic cancer patients. Results: AIP and pancreatic cancer were detected as high-signal intensity areas on DWI. In all AIP cases, the enlarged pancreas was reduced and the ADC values were increased after the start of treatment. The ADC values of AIP patients were 0.90×10-3 mm2/s (0.82-0.95×10-3 mm2/s) before steroid therapy, and were 1.19×10-3 mm2/s (1.06-1.21×10-3 mm2/s) after one week. They were 1.41×10-3 mm2/s(1.32-1.44×10-3 mm2/s) after one month from the start of treatment. The ADC values of the pancreatic cancer patients were 1.26×10-3 mm2/s (1.20-1.35×10-3 mm2/s) and were significantly higher than those of the AIP patients before steroid therapy. Conclusion: DWI is non-invasive and useful for evaluating the effects of steroid therapy for AIP. The ADC values may be useful for distinguishing AIP from pancreatic cancer.