Characters of patients with different types of pancreatitis
RAP refers to a clinical entity characterized by episodes of acute pancreatitis which occurs on more than one occasion. An established chronic disease may be found either on the occasion of the first episode of pancreatitis or during the follow-up. RAP was the strongest predicting factor for a subsequent diagnosis of CP [4, 26, 27]. The etiology and epidemiology of AP, RAP and CP were studied in this research. The results showed that coagulation disorder is related to AP and RAP group, with OR of13.88 and 12.53 (P<0.01) respectively compared with patients in control group, and D-dimer levels in AP and RAP groups were significantly higher than those of the control group. However, coagulation disorder and D-dimer levels had no significant difference between CP group and control group. The D-dimer level is also related to the severity of pancreatitis. This result was confirmed in other studies, which showed that D-dimer was an early predictor of the severity of AP [28-30]. The possible mechanism may be two-sided: the abnormal activation of pancreatic enzymes results in inflammation and injury to the pancreas at the onset of AP, which then induces thrombosis and further aggravates the injury[31, 32]. The systemic inflammatory response syndrome and multiple organ dysfunction syndromes, which occur in patients with AP, are common risk factors for the development of VTE [33]. The propagation of the acute inflammatory response can lead to chronic inflammation if there is no appropriate resolution [34, 35]. On a molecular level, pancreatic stellate cells (PaSCs) have been found to play an important role in models of CP. In CP, PaSCs participate in pathogenesis after transforming into an activated or “myofibroblastic” state [36]. In this myofibroblastic state, PaSCs produce collagen and other extracellular matrix proteins that lead to fibrosis. PaSCs also secrete cytokines which further promote the inflammatory process[36]. However, the D-dimer levels of CP patients were not very different from those of the control group; the reason may be that the severity of inflammation in CP patients was less than that of AP and RAP groups. Besides, the fibrotic changes of the pancreas may not induce acute inflammation and coagulation disturbance. A study about splanchnic venous thrombosis (SVT) suggested that local inflammation plays a major role in SVT causation. Thrombophilia caused by coagulation disturbance is seen in one-third of patients with AP but does not seem to increase the risk of SVT[37].
Our study shows that dyslipidemia is related to different types of AP, RAP and CP, with OR of 8.40, 10.24 and 2.46 (p<0.05) respectively, and dyslipidemia is also related to D-Dimer level. In previous studies, dyslipidemia, especially hypertriglyceridemia, is related to AP and RAP [38], the pathophysiology could be the metabolism of excessive TGs by pancreatic lipase to free fatty acids (FFA) leading to pancreatic cell injury and ischemia [39]. A 3558-patient study comparing high triglyceride-AP (HTG-AP) versus non-HTG-AP s reported a statistically significant higher incidence of pancreatic necrosis, infected pancreatic necrosis, organ failure, and persistent organ failure [40]. Recent studies demonstrate a trend towards severity in patients with HTG-AP when compared with non-HTG pancreatitis patients; the patients with higher TGs levels appear to have more severe hospital courses with a higher incidence of complications (35-69%) and organ failure (20-35%)[41]. Researches have shown that patients with diabetes, obesity, or metabolic syndrome due to insulin resistance tend to have low HDL-C because of lower lipoprotein lipase activity and triglyceride enrichment, but the mechanism is still unknown [42-44]. The TG/HDL-C ratio was found to be associated with insulin resistance in overweight and obese children[45]. Our research shows that in AP and RAP patients, TG and FFA levels of which were significantly higher than those of CP and control group, HDL-C levels of AP, RAP and CP groups were lower than those of the control group (p<0.05), TG/HDL-C ratios of AP, RAP and CP groups were significantly higher than those of the control group (p<0.05), which may be related to insulin resistance in all types of pancreatitis[46, 47]. TG/HDL-C ratio is also a potential useful marker to identify the severity of RAP patients in clinical practice, with positive predictive value of 0.84 at 3.51 cut-off point. TG/HDL-C ratio was related to insulin resistance, which may occur after acute pancreatitis[48]. In our research, TG/HDL-C ratio is found to be a predictor of severity in RAP patients but not in first attack of AP. The mechanism may be that hypertriglyceridemia (HTG) is a well-established cause of RAP, and TG/HDL-C ratio is predictable in RAP. The relationship between insulin resistance and RAP should be further investigated [39].
We also found that D-dimer level was related to TG/HDL-C ratio (r=0.379, p<0.01), a previous study has shown that both TG and acute pancreatitis could cause an elevation in d-dimer level, in which TG plays a more important role[49]. In type 2 diabetic children and adolescent, D-dimer level was significantly correlated with TG (p<0.05)[50]. Our research showed that TG was related to D-dimer level in RAP group, the AUC of TG in elevated D-dimer group were less than AUC of TG/HDL-C ratio, the correlation coefficient between TG and D-dimer is less than TG/HDL-C ratio and D-dimer level. So TG/HDL-C could be used as a better predictor for RAP severity and elevated D-dimer level.
Alcoholism is also a risk factor of all types of pancreatitis. Recent data from predominant western countries have shown an increasing trend in the incidence of acute pancreatitis and the number of hospital admissions for both acute and chronic pancreatitis [51-53]. The pathogenesis may be PSCs, which are activated directly by alcohol and its metabolites, and also by cytokines and growth factors released during alcohol-induced pancreatic necroinflammation. Activated PSCs are the key cells responsible for fibrosis of alcoholic chronic pancreatitis[54]. Our research shows that alcoholism is related to AP, RAP and CP groups, with OR of 6.74, 7.41 and 18.89 (p<0.01) respectively.
Our research shows that diabetes is related to RAP and CP. The pathogenesis is that RAP and CP, which are pancreatic inflammation with irreversible parenchymal damage and functional changes, is complicated by progressive nutrient maldigestion, glucose intolerance, diabetes mellitus, and metabolic derangements [55]. Destruction of islet cells by pancreatic inflammation can lead to the development of “brittle” disease with wide swings in blood sugar which are difficult to control. Besides, patients may have pre-existing risk factors for type 2 diabetes, such as insulin resistance, obesity, or dietary habits that further complicate the optimal regulation of glucose metabolism[56-58]. In our study, diabetes was related to RAP and CP groups, with OR of 7.73 and 6.71 (p<0.05), but had no relationship to the AP group.
In our study, heart disease is related to RAP, with OR of 10.15 (p<0.05). So far, research on association between heart and pancreas disease has been paid little attention and its role in pathogenesis is not fully elucidated. The pathogenesis could be pancreatic enzymes and their inhibitors that profoundly affected blood coagulation and appear to influence the course of pancreatic inflammation [59]. Researches have shown that in patients with chronic heart failure, the splanchnic circulation is decreased, especially in highly vascularized pancreas , which may cause pancreatitis [60].
There are no significant differences in other factors like smoking, hypertension, etc. between pancreatitis and the control group. Although we drew similar conclusions from recent studies, our research had significant advantages. We distinguished different types of pancreatitis between AP, RAP and CP groups. RAP is a syndrome of multiple distinct acute inflammatory responses originating within the pancreas in individuals with genetic, environmental, traumatic, morphologic, metabolic, biologic, and/or other risk factors who experienced 2 or more episodes of documented AP, and RAP may lead to chronic pancreatitis [61]. Approximately 9% to 31% of patients with AP develop RAP [62, 63]. To our knowledge, no similar investigations about a comparison between AP, RAP and CP groups have been investigated in China. In our research, the epidemiology and etiological factors of RAP are similar to those of first attack AP; also D-Dimer levels and dyslipidemia were similar in the RAP and the AP groups. However, the D-Dimer level, dyslipidemia and severity of pancreatitis in CP group were similar to those of the control group.
The present research has several limitations. Firstly, it was conducted in a single center with a relatively small sample, which may create bias. Secondly, we did not take into account some inflammation factors, such as PCT, C-reactive protein and interleukin-6; or arterial blood gases, which are also useful predictors of severity in AP[64, 65], because they were not routinely analyzed at admission in Qilu Hospital. Besides, we used BISAP score instead of APACH-Ⅱ score to analyze the severity of pancreatitis because some test results needed in the APACH-Ⅱ score system were not available, and research had confirmed that BISAP is as useful as APACHE-II and more effective than Ranson criteria, CTSI, CRP, HCT and BMI in predicting severity, organ failure, and death in patients with acute pancreatitis[25]. However, it may still create bias, especially when compared with other studies.