Diagnosis of autoimmune pancreatitis

Table 2 Diagnosis of definitive and probable type 1 autoimmune pancreatitis using international consensus diagnostic criteria[25]

Diagnosis	Primary basis for diagnosis	Imaging evidence	Collateral evidence
Definitive type 1 AIP	Histology	Typical/indeterminate	Histologically confirmed LPSP (level 1 H)
	Imaging	Typical	Any non-D level 1/level 2
		Indeterminate	Two or more from level 1 (+ level 2 D1)
	Response to steroid	Indeterminate	Level 1 S/OOI + Rt or level 1 D +
			Level 2 S/OOI/H + Rt
Probable type 1 AIP		Indeterminate	Level 2 S/OOI/H + Rt
Criterion	Level 1		Level 2
P: Parenchymal imaging	Typical:		Indeterminate (including atypical3):
	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)
S: Serology	IgG4, > 2 × upper limit of normal value		IgG4, 1-2 × upper limit of normal value
OOI: Other organ involvement	a or b		a or b
	a: Histology of extrapancreatic organs		a: Histology of extrapancreatic organs including endoscopic biopsies of bile duct4:
	Any three of the following:		Both of the following:
	(1) Marked lymphoplasmacytic infiltration with fibrosis and without granulocytic infiltration		(1) Marked lymphoplasmacytic infiltration without granulocytic infiltration
	(2) Storiform fibrosis		(2) Abundant (> 10 cells/HPF) IgG4-positive cells
	(3) Obliterative phlebitis
	(4) Abundant (> 10 cells/HPF) IgG4-positive cells
	b: Typical radiological evidence		b: Physical or radiological evidence
	At least one of the following:		At least one of the following
	(1) Segmental/multiple proximal (hilar/intrahepatic) or proximal and distal bile duct stricture		(1) Symmetrically enlarged salivary/lachrymal glands
	(2) Retroperitoneal fibrosis		(2) Radiological evidence of renal involvement described in association with AIP
H: Histology of the pancreas	LPSP (core biopsy/resection)		LPSP (core biopsy)
	At least 3 of the following:		Any 2 of the following:
	(1) Periductal lymphoplasmacytic infiltrate without granulocytic infiltration		(1) Periductal lymphoplasmacytic infiltrate without granulocytic infiltration
	(2) Obliterative phlebitis		(2) Obliterative phlebitis
	(3) Storiform fibrosis		(3) Storiform fibrosis
	(4) Abundant (> 10 cells/HPF) IgG4-positive cells		(4) Abundant (> 10 cells/HPF) IgG4-positive cells
Response to steroid (Rt)2		Diagnostic steroid trial
	Rapid ( ≤ 2 wk) radiologically demonstrable resolution or marked improvement in pancreatic/extrapancreatic manifestations

¹Level 2 D is counted as level 1 in this setting;

²Diagnostic 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;

³Atypical: 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);

⁴Endoscopic biopsy of duodenal papilla is a useful adjunctive method because ampulla often is involved pathologically in AIP. AIP: Autoimmune pancreatitis; ICDC: International consensus diagnostic criteria; HPF: High power field; LPSP: Lymphplasmacytic sclerosing; OOI: Other organ involvement.