Pancreatic volume change using three dimensional-computed tomography volumetry and its relationships with diabetes on long-term follow-up in autoimmune pancreatitis.

Background: Several studies found that early pancreatic atrophy detected by computed tomography (CT) within 6 months was associated with a high incidence of diabetes in patients with type-1 autoimmune pancreatitis (AIP) receiving steroid therapy; however, no long-term follow-up studies have been performed.

Aim: To investigate pancreatic volume (PV) changes using three dimensional (3D)-CT volumetry and their relationship with IgG4 and diabetes in patients with AIP.

Methods: This retrospective study included 33 patients with type-1 AIP receiving steroid therapy. Patients were divided into diffuse (D-type) and mass-forming type (M-type) AIP. PV was determined by semi-automated 3D-CT volumetry, and changes between initial and follow-up values were calculated. The relationship between PV and serum IgG4 levels was analyzed by Spearman's rank correlation. The PV atrophy ratio compared with the presumed normal PV at the time of last follow-up CT and its relationship with diabetes were investigated.

Results: There were 16 D-type and 17 M-type patients with long-term follow-up (mean, 95.8 months). The regression curve of mean relative PV change reduced exponentially and rapidly during the first 25 months and then more slowly in both groups. The overall cumulative pancreas re-enlargement rates at 1, 3, 5, 7 and 10 years were 6.1%, 12.2%, 29.2%, 47.5% and 55.0%, respectively. There was a moderate-to-very strong positive correlation ( ≥ 0.4) between PV and serum IgG4 levels in nine (9/13, 69.2%) patients. All 33 patients showed pancreatic atrophy (mean 59.3%) after long-term follow-up. Patients with D-type AIP had a significantly higher atrophy rate and higher incidence of diabetes than M-type patients ( < 0.05).

Conclusion: PV change initially reduced exponentially and then more slowly and is considered an important factor associated with diabetes. Serum IgG4 levels were positively correlated with PV during follow-up.