Comparison of clinical and histopathological features between serum IgG4-negative and serum IgG4-positive patients with type 1 autoimmune pancreatitis: A single-center, retrospective study.

OBJECTIVE: In type 1 autoimmune pancreatitis (AIP), serum immunoglobulin G4 (IgG4) has a complex correlation with pathology. In this study, clinical/histopathological traits of serum IgG4-negative/positive (N/P) patients were compared, and serum IgG4-tissue IgG4 correlations were explored to aid accurate diagnosis/typing. MATERIAL AND METHODS: A retrospective analysis was performed on 78 type 1 AIP patients (screened from 160 eligible cases through inclusion/exclusion criteria, International Consensus Diagnostic Criteria-confirmed at Changhai Hospital (December 2019-2023). At diagnosis, patients with serum IgG4 <135 mg/dL (n = 19) were assigned to the serum IgG4-N group, and those with serum IgG4 ≥135 mg/dL (n = 59) were assigned to the serum IgG4-P group. Clinical baseline data, laboratory indicators, imaging features (computed tomography/magnetic resonance imaging/endoscopic ultrasound guided [EUS]), and histopathological findings (from EUS fine-needle aspiration/fine-needle biopsy [EUS-FNA/FNB] or surgery) were compared. Statistical analysis (R 4.4.0) was conducted with Chi-square/Fisher's exact tests (categorical data) and Mann‒Whitney U tests (continuous data); Spearman correlation was used to assess serum IgG4-tissue IgG4 links. A Bonferroni-corrected P <0.050 was considered to indicate statistical significance. RESULTS: No significant differences in sex, age, most comorbidities (e.g., hypertension), or symptoms (e.g., abdominal discomfort) were observed between the serum IgG4-N and serum IgG4-P groups (all P > 0.050). The rate of bile duct stenosis was higher in the serum IgG4-P group than in the serum IgG4-N group (55.93% vs. 26.32%, P = 0.047), as were the rates of EUS examination (84.75% vs. 52.63%, P = 0.010), EUS-FNA/FNB (84.75% vs. 52.63%, P = 0.010). The 84.75% vs 52.63% (P = 0.010) represents the EUS examination receiving rate between serum IgG4-P and serum IgG4-N groups, rather than the diagnostic positive rate of FNA/FNB subtypes. The serum IgG4-P group also had a higher histopathological confirmation rate (71.19% vs. 36.84%, P = 0.015) and a greater median number of tissue IgG4-P cells (36 vs. 8 cells per high-power field (HPF), P = 0.035). In contrast, the serum IgG4-N group had a higher median carbohydrate antigen 19-9 (CA19-9) level (32.14 vs. 5.97 U/mL, P = 0.035), a higher rate of long/multiple pancreatic duct narrow sections (30% vs. 2%, P = 0.013), and a higher surgical rate (47.37% vs. 15.25%, P = 0.010). Across both groups, no significant correlation was detected between serum IgG4 levels and tissue IgG4-P plasma cell counts (Spearman's rho = 0.113, P = 0.322; linear regression coefficient = 0.004, P = 0.538). CONCLUSION: Serum IgG4 typing is associated with the clinical-pathological features of type 1 AIP. The serum IgG4-P group often shows biliary duct stenosis and diffuse pancreatic enlargement, with a reliance on EUS puncture. The serum IgG4-N group has higher CA19-9 and a higher surgical rate. Pathological examination remains critical (no serum-tissue IgG4 association). This study supports optimized, accurate diagnosis and stratified management of type 1 AIP.