Diagnosis of autoimmune pancreatitis

Table 1 Clinical diagnostic criteria for autoimmune pancreatitis in 2011 by Japan Pancreas Society (JPS-2011)[16]

A: Diagnostic items

I: Enlargement of the pancreas:

(a) Diffuse enlargement

(b) Segmental/focal enlargement

II: ERP (endoscopic retrograde pancreatography) shows irregular narrowing of the main pancreatic duct

III: Serological findings

Elevated level of serum IgG4 (≥ 135 mg/dL)

IV: Pathological findings: Among (1)-(4) listed below

(a) Three or more are observed

(b) Two are observed

(1) Prominent infiltration of lymphocytes and plasmacytes and fibrosis

(2) More than 10 IgG4-positive plasmacytes per high-power microscope field

(3) Storiform fibrosis

(4) Obliterative phlebitis

V: Extra-pancreatic lesions: sclerosing cholangitis, sclerosing dacryoadenitis/sialoadenitis/retroperitoneal fibrosis

(a) Clinical lesions

Extrapancreatic sclerosing cholangitis, sclerosing dacryoadenitis/ sialoadenitis (Mikulicz disease) or/retroperitoneal fibrosis

(b) Pathological lesions

Pathological examination shows characteristic features of sclerosing cholangitis, sclerosing dacryoadenitis sialoadenitis or/retroperitoneal fibrosis

<Option> Effectiveness of steroid therapy

A specialized facility may include in its diagnosis the effectiveness of steroid therapy, once pancreatic or bile duct cancers have been ruled out. When it is difficult to differentiate from malignant conditions, it is desirable to perform cytological examination using an endoscopic ultrasound-guided fine needle aspiration (EUS-FNA). Facile therapeutic diagnosis by steroids should be avoided unless the possibility of malignant tumor has been ruled out by pathological diagnosis.

B: Diagnosis

I: Definite diagnosis

(1) Diffuse type

Ia + III/IVb/V (a/b)

(2) Segmental/focal type

Ib + II + two or more of < III/IVb/V (a/b) >

or

Ib + II + < III/IVb/V (a/b) > + Option

(3) Definite diagnosis by histopathological study

IVa

II: Probable diagnosis

Segmental/focal type: Ib + II + < III/IVb/V(a/b) >

III: Possible diagnosis1

Diffuse type: Ia + II + Option

Segmental/focal type: Ib + II + Option

When a patient with a focal/segmental image of AIP on CT/MRI without ERCP findings fulfill more than one of III, Ivb and V (a/b) ERP criteria, he/she can be diagnosed as probable AIP only after the negative workup for malignancy by EUS-FNA, and confirmed as definitive one by an optional steroid response.

¹Possible diagnosis: A case may possibly be type 2, although it is extremely rare in Japan. AIP: Autoimmune pancreatitis; CT: Computed tomography; MRI: Magnetic resonance image.