Objective: We retrospectively studied the timing of radiological improvement after steroid therapy in patients with autoimmune pancreatitis (AIP).
Material and methods: Patients with AIP (n = 31) received steroids followed by diagnostic imaging within 1 month. Pancreatic swelling, pancreatic and bile duct features, and apparent diffusion coefficient (ADC) were compared before and after treatment. The period from treatment initiation to evaluation was divided into five phases: early phase (days 3-5), week 1 (days 6 and 7), week 2 (days 8-14), week 3 (days 15-21), and week 4 (days 22-28). Five gastroenterologists evaluated pancreatic swelling and duct features (good/intermediate/no response), and the "good response" rate (response rate) was calculated for each phase. In addition, pancreatic volumes were measured with a 3D workstation before and after treatment, and the percentage change in volume was calculated. ADC values were calculated in 14 patients.
Results: The median ratio of pancreatic volume after relative to before treatment was 0.89, 0.79, 0.67, 0.59, and 0.47 for early phase, week 1, week 2, week 3, and week 4, respectively. The response rate of the pancreatic swelling was 37.5%, 57.1%, 83.3%, 100%, and 100%; response rate of the pancreatic duct was 0%, 20%, 75%, 75% and 100%; and response rate of the bile duct was 0%, 66.7%, 83.3%, 100%, and 80%. The ADC increased after treatment in all 14 patients, including the 7 patients evaluated in the early phase.
Conclusions: Evaluation of pancreatic swelling and duct features is recommended in week 2 and thereafter. The ADC increased soon after treatment initiation, suggesting its usefulness for evaluating early treatment responses.
Keywords: apparent diffusion coefficient; autoimmune pancreatitis; diffusion-weighted imaging; steroid.