autoimmune pancreatitis has travelled a relatively short way from its first description by sarles et al . in 1961   to the formal suggestion of the very concept of autoimmune pancreatitis by yoshida et al . in 1995 , and its subsequent inclusion in a new group of diseases with systemic involvement associated with an increase in serum igg4 levels , after the depiction by kamisawa et al . . most descriptions have , up to now , been done on asian patients , even though there have been descriptions of patients in other geographical areas [ 4 , 5 ] . in spite of the scant information available , mainly due to the few reported cases of the disease and its aforementioned  short  history , it is possible to assert that there are some differences in the clinical presentation of patients of different ethnicities . in conjunction with the scarcity of available information , there is the added problem that until recently , there is a lack of universally recognised criteria for the diagnosis of the disease . asian , european , and north american consensus have so far been published [ 68 ] and most centers use distinct criteria , making difficult to establish comparison among patients in whom the diagnosis was made at different geographical areas . recently , an international panel of experts met to develop the international consensus diagnostic criteria for autoimmune pancreatitis to favor the worldwide recognition of the illness . in this consensus , emphasis is placed on the advantages of classifying autoimmune pancreatitis into either of two types : lymphoplasmocytic sclerosing pancreatitis ( lpsp ) and idiopathic duct - centric pancreatitis ( idcp ) , since it has been so far ascertained that there are significant variations in clinical presentation , depending on the histological characteristics of the pancreatitis under study . for this reason , it is important to obtain clinical descriptions of the disease , together with its histopathological characteristics , as this will allow us to lay the foundations for our understanding of the disease behaviour . the aim of this study is to identify and describe the general characteristics of patients diagnosed with autoimmune pancreatitis at a third - level hospital in mexico . from our hospital records , we identified 15 patients who met the histological criteria for autoimmune pancreatitis . a mexican mestizo is defined as an individual who was born in mexico and is a descendant from the native inhabitants of such region , and from individuals , mainly spaniards of white or african origin , or both , who came to america during the 16th century . the cut - off was 1868  mg / dl and 135  mg / dl , respectively . immunohistochemical staining for igg4 was performed in all cases and was considered positive with > 10 igg4-positive plasma cells per high power field ( hpf ) . subtype classification as either lymphoplasmocytic sclerosing pancreatitis ( lpsp ) or idiopathic duct centric pancreatitis ( idcp ) was performed according to the 2011 international consensus diagnostic criteria for autoimmune pancreatitis . available pretreatment computed tomography ( ct ) scans ( n = 13 ) were reviewed by a single radiologist , while in 2 patients only written radiological reports were at hand . pancreatic enlargement was defined as an increase in size of the gland in the absence of a discrete mass . mass was defined as a lesion that had different density compared with surrounding pancreatic tissue . biliary and pancreatic duct strictures were considered steroid - responsive if follow - up imaging showed normal biliary tree and pancreatic duct , respectively . pancreatic mass / enlargement was considered steroid - responsive if abnormality resolved , with posttherapy imaging showing normal - appearing pancreas or pancreatic atrophy . given the lack of immediate accessibility to serum igg4 measurements as a marker of disease , we remained without this response criterion . patient 's demographic and clinical characteristics at the outbreak of the disease are shown on table 1 . patients were followed up at our institute for 34.9 months ( range from 2 to 84 months ) . throughout this period , four episodes of acute pancreatitis were reported and four patients were classified as having chronic pancreatitis . moreover , weight loss was documented in 13 patients , with a mean loss of 13.3  6  kg . the median of total igg was 2400  mg / dl ( range : 1060  mg / dl4740  mg / dl ) . the two patients with elevated levels of igg4 had values of 264  mg / dl and 591  mg / dl , with total igg of 1060  mg / dl and 1670  mg / dl , respectively , both within normal values of total igg . additional sites of igg4 + plasma cell infiltration were histopathologically identified in 9 patients , some of them with more than one infiltration site : myofibroblastic tumour ( n = 3 ) , lymph node infiltration ( n = 6 ) , palate ( n = 1 ) , lacrimal gland ( n = 1 ) , salival gland ( n = 1 ) , gallbladder ( n = 2 ) , prostate ( n = 1 ) , orbit ( n = 1 ) , liver ( n = 1 ) , and kidney ( n = 1 ) . nine patients ( 60% ) underwent major abdominal surgery ( biliodigestive derivation or whipple procedure ) . radiological data before treatment were available for review in 13 patients , for the other 2 cases only written radiological reports were analyzed . twelve patients had evidence of pancreatic enlargement as previously defined , 3 of this cases were interpreted as having a mass . the most common extrapancreatic involvement identified was abdominal lymphadenopathy in 5/15 cases , followed by interstitial lung involvement in 4/15 cases , and finally 3/15 patients had evidence of glandular involvement on head ct . glandular organs , including pancreas , lachrymal glands , and minor and major salivary glands , showed predominantly acinar atrophy and a variable degree of interstitial and periductal inflammatory infiltrate with abundant plasma cells and fibrosis . lymph nodes , including peripancreatic ones , had follicular hyperplasia and dilated sinuses with abundant plasma cells . all cases met criteria for lpsp ( type 1 ) . a total of 8 patients were treated with steroids . all of them received oral prednisone at doses of at least 20  mg / qd . all patients responded to treatment and , to this day , none has relapsed although this is not yet significant as the follow - up time from the beginning of treatment has been brief due to delay in diagnosis establishment . as was previously mentioned , two main histopathological variants of autoimmune pancreatitis are currently recognised , and they behave clinically in quite different manners . the recently established international consensus has suggested the use of this classification , but this is not , however , always feasible due to the need of a sufficiently large sample of tissue for a pathologist to study . in this work , we introduce the first series of cases of autoimmune pancreatitis in the mexican population , all of them confirmed by histopathological analysis . the review of these cases showed that all patients corresponded to the lpsp variant , which is the most frequently reported , even though our patients ' mean age was much lower than that expected for this histological type ( mean age of 61.6 versus 47.5 for out population ) . nowadays , it is recognised that one of the most common symptoms is obstructive jaundice ; however , we found it with a lower frequency than that previously reported , since in asian patients the frequency goes from 74 to 88% [ 12 , 13 ] , whereas only 53% of our patients had this symptom at the onset of the disease . it is worth remarking that we found a relatively high frequency of acute pancreatitis , which in a recent multicentre study was mainly associated to idcp . abdominal pain was also reported with a higher frequency than expected according to previous reports . extrapancreatic involvement has been mainly associated to lpsp with , in some cases , 2 to 4 organs affected . this is congruent with our findings , as we found 9/15 patients with multiorgan involvement , although organ involvement could probably be more common but pass unnoticed for not making a direct search of it . it is important to point out that , due to the clinical presentation of this disease , the differential diagnosis is established mainly with pancreas cancer . in this regard , even though pancreatic mass was identified in only 3 patients , pancreatic growth in the imagining study was found in 12 patients which , in conjunction with the weight loss in the majority , gave rise to a high rate of surgeries ( biliodigestive derivation or whipple procedure ) . in order to avoid this , one of the main elements that hint at a diagnosis of autoimmune pancreatitis before the surgery alternative is the increase in serum igg4 , which has been found to be high in 75% of patients in some series [ 16 , 17 ] . in this concern , there are two important points in our series : firstly , igg4 measurement was requested in only 10/15 patients , which indicates the low suspicion levels prevalent with regard to the disease , something that we hope will change soon ; secondly , that only 20% of our patients showed an increase in serum igg4 levels , which goes against what has been reported up to now . the search for cases was based on histopathological results , and perhaps if a systematic measurement of igg4 serum levels in patients suspected of harboring the disease had taken place , a greater prevalence of high igg4 would have been found . be this as it may , only a systematic study of this pathology within our ethnic group can really answer whether these observations are truly an atypical manifestation . recently published the clinical characteristics of patients with igg4-negative autoimmune pancreatitis , in which there were differences with respect to those patients that showed an increase , and these patients seem closer to the presentation of our cases . in conclusion , autoimmune pancreatitis is a disease that is currently undergoing a process of definition of its clinical and diagnostic characteristics . the first cases are being found within our population , and a greater body of evidence is still being needed in order to establish clearly its presentation mode . notwithstanding this , this series results seem to indicate that , within the mexican population , patients with autoimmune pancreatitis with lpsp are affected from the disease at an earlier age , with a low percentage rate for high igg4 serum levels , and with the main symptoms being abdominal pain , pancreatitis , weight loss , and obstructive jaundice .
autoimmune pancreatitis is part of the spectrum of igg4-associated diseases . 
 its diagnostic criteria and histological subtypes have been formally proposed recently and although based on current data it has been suggested that there are differences in clinical presentation among populations , more research is needed to properly establish if this heterogeneity exists . in this paper , we describe 15 cases of autoimmune pancreatitis diagnosed at a mexican centre of reference , all of them associated to the lymphoplasmocytic sclerosing pancreatitis variant . 
 the mean age at the onset of symptoms was 47.5  14.4 years , and 53% of patients were male . 
 the main manifestations were weight loss ( 87% ) , obstructive jaundice ( 53% ) , and acute ( 27% ) and chronic ( 27% ) pancreatitis . 
 only 20% of patients had high igg4 serum levels at the time of diagnosis . 
 all patients receiving prednisone responded favourably , both in their pancreatic and extrapancreatic manifestations . 
 clinical manifestations of mexican patients showed certain differences with respect to those usually reported .