As emphasized in Chap. 313, the etiologies as well as the clinical manifestations of pancreatitis are quite varied. Although it is well-appreciated that pancreatitis is frequently secondary to biliary tract disease and alcohol abuse, it can also be caused by drugs, trauma, and viral infections and is associated with metabolic and connective tissue disorders. In ∼30% of patients with acute pancreatitis and 25−40% of patients with chronic pancreatitis, the etiology initially can be obscure.
Although good data exist concerning the incidence of acute pancreatitis (about 5−35/100,000 new cases per year worldwide, with a mortality rate of about 3%), the number of patients who suffer with acute pancreatitis is largely increasing and is now estimated to be 70 hospitalizations/100,000 persons annually, resulting in >200,000 new cases of acute pancreatitis per year in the United States. Only one prospective study on the incidence of chronic pancreatitis is available; it showed an incidence of 8.2 new cases per 100,000 per year and a prevalence of 26.4 cases per 100,000. These numbers probably underestimate considerably the true incidence and prevalence, because non alcohol−induced pancreatitis has been largely ignored. At autopsy, the prevalence of chronic pancreatitis ranges from 0.04 to 5%. The relative inaccessibility of the pancreas to direct examination and the nonspecificity of the abdominal pain associated with pancreatitis make the diagnosis of pancreatitis difficult and usually dependent on elevation of blood amylase and/or lipase levels. Many patients with chronic pancreatitis do not have elevated blood amylase or lipase levels. Some patients with chronic pancreatitis develop signs and symptoms of pancreatic exocrine insufficiency, and, thus, objective evidence for pancreatic disease can be demonstrated. However, there is a very large reservoir of pancreatic exocrine function. More than 90% of the pancreas must be damaged before maldigestion of fat and protein is manifested. Noninvasive, indirect tests of pancreatic exocrine function (fecal elastase) are much more likely to give abnormal results in patients with obvious pancreatic disease (i.e., pancreatic calcification, steatorrhea, or diabetes mellitus, than in patients with occult disease). Thus, the number of patients who have subclinical exocrine dysfunction (<90% loss of function) is unknown.
Tests Useful in the Diagnosis of Pancreatic Disease
Several tests have proved of value in the evaluation of pancreatic disease. Examples of specific tests and their usefulness in the diagnosis of acute and chronic pancreatitis are summarized in Table 312-1 and Fig. 312-1. At some institutions, pancreatic-function tests are available and performed if the diagnosis of pancreatic disease remains a possibility after noninvasive tests [ultrasound, CT, magnetic resonance cholangiopancreatography (MRCP)] or invasive tests [endoscopic retrograde cholangiopancreatography (ERCP), endoscopic ultrasonography (EUS)] have given normal or inconclusive results. In this regard, tests employing direct stimulation of the pancreas are the most sensitive.
Table 312-1 Tests Useful in the Diagnosis of Acute and Chronic Pancreatitis and Pancreatic Tumors