Diagnosis of autoimmune pancreatitis

Table 3 Diagnosis of definitive and probable type 2 autoimmune pancreatitis using international consensus diagnostic criteria[25]

Diagnosis	Imaging evidence	Collateral evidence
Definitive type 2 AIP	Typical/indeterminate	Histologically confirmed IDCP (level 1 H) or clinical inflammatory bowel disease + level 2 H + Rt
Probable type 2 AIP	Typical/indeterminate	Level 2 H/clinical inflammatory bowel disease + Rt
Criterion	Level 1	Level 2
P: Parenchymal imaging	Typical:	Indeterminate (including atypical2):
	Diffuse enlargement with delayed enhancement (sometimes associated with rim-like enhancement)	Segmental/focal enlargement with delayed enhancement
D: Ductal imaging (ERP)	Long (> 1/3 length of the main pancreatic duct) or multiple strictures without marked upstream dilatation	Segmental/focal narrowing without marked upstream dilatation (duct size, < 5 mm)
OOI: Other organ involvement		Clinically diagnosed inflammatory bowel disease
H: Histology of the pancreas (core biopsy/resection)	IDCP
	Both of the following:	Both of the following:
	(1) Granulocytic infiltration of duct wall (GEL) with or without granulocytic acinar inflammation	(1) Granulocytic and lymphoplasmacytic acinar infiltrate
	(2) Absent or scant (0-10 cells/HPF) IgG4-positive cells	(2) Absent or scant (0-10 cells/HPF) IgG4-positive cells
Response to steroid (Rt)1	Diagnostic steroid trial
	Rapid ( ≤ 2 wk) radiologically demonstrable resolution or marked improvement in manifestations

¹Diagnostic steroid trial should be conducted carefully by pancreatologists with caveats (see text) only after negative workup for cancer including endoscopic ultrasound-guided fine needle aspiration;

²Atypical: Some AIP cases may show low-density mass, pancreatic ductal dilatation, or distal atrophy. Such atypical imaging findings in patients with obstructive jaundice and/or pancreatic mass are highly suggestive of pancreatic cancer. Such patients should be managed as pancreatic cancer unless there is strong collateral evidence for AIP, and a thorough workup for cancer is negative (see algorithm). AIP: Autoimmune pancreatitis; ICDC: International consensus diagnostic criteria; IDCP: Idiopathic duct-centritic pancreatitis.