Autoimmune Pancreatitis Re-Classification with Novel Type AIP-4

Autoimmune pancreatitis (AIP) represents a rare multifaceted disorder group with currently three types that were recently supplemented by a newly described AIP type causally related to sunlight exposure, not previously reported in any of the AIP publications. The internet search disclosed that the new AIP type was different from three existing AIP types: the AIP-1 or AIP-2 types, both featured by idiopathy, and the AIP-3 type, triggered by immune checkpoint inhibitors. Accordingly, it seemed appropriate to classify the novel AIP as the AIP-4 type, with typical features such as a clear culprit of sunlight exposure, ascertained by a positive result of an unintentional re-exposure and considered a diagnostic gold standard; coexisting secondary sclerosing cholangitis without progression to vanishing bile duct syndrome; and ultimately unavoidable pancreatic atrophy with clinical exocrine insufficiency despite long-term treatment with immunosuppressive drugs. Thus, the recent description of a new AIP type, now classified as the AIP-4 type, is strongly associated with significant sunlight exposure and calls for a reclassification of AIP types that includes AIP-4, whereby additional efforts are essential to identify the causative factors of the AIP-1 and AIP-2 types, including drugs commonly used in the respective cohorts, which also comprise older patients with comorbidities.