*4.5.1 When to perform EUS and FNA? Value of cytology and biopsy in differential diagnoses.*

Diagnosis of type 1 AIP can be made with high certainty in many patients: clinical symptoms, characteristic images supported by elevated serum IgG4 level, and other organ involvement can assure the diagnosis without pancreatic histology. However, in the absence of these latter conditions, establishing the definitive diagnosis of even type 1 AIP can be difficult. In type 2 AIP, IgG4 is practically never increased, and IBD is the only associated pathology, but only probable diagnosis can be done without histology. With the availability of new biopsy needles (shark, core biopsy), which permit to obtain a small tissue cylinder, diagnostic performance of pancreatic biopsy has dramatically increased, without major risk of complications: clinically significant hemorrhage and pancreatitis are rare, below 1%. Thus, biopsy should be considered in every patient with a suspicion of seronegative type 1 and in type 2 AIP, preferably before initiating a relatively long steroid treatment.
