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GENERAL CONSIDERATIONS
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As emphasized in Chap. 341, the etiologies as well as 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, genetic mutations, 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.
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The incidence of acute pancreatitis is about 5–35 per 100,000 new cases per year worldwide, with a mortality rate of about 3%. The incidence of chronic pancreatitis is about 4–8 per 100,000 persons with a prevalence of 26–42 cases per 100,000. The number of patients admitted to the hospital who suffer with both acute and chronic pancreatitis in the United States is largely increasing and is now estimated to be 274,119 for acute pancreatitis and 19,724 for chronic pancreatitis. Acute pancreatitis is the most common gastrointestinal diagnosis requiring hospitalization in the United States. Acute and chronic pancreatic disease costs an estimated $3 billion annually in health care expenditures. These numbers may underestimate 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%.
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The diagnosis of acute pancreatitis is generally clearly defined based on a combination of laboratory, imaging, and clinical symptoms. The diagnosis of chronic pancreatitis, especially in mild disease, is hampered by the relative inaccessibility of the pancreas to direct examination and the nonspecificity of the abdominal pain associated with chronic pancreatitis. 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 (PEI), 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 advanced pancreatic disease (i.e., pancreatic calcification, steatorrhea, or diabetes mellitus) than in patients with occult disease. Invasive, direct tests of pancreatic secretory function (secretin tests) are the most sensitive and specific tests to detect early chronic pancreatic disease when imaging is equivocal or normal.
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TESTS USEFUL IN THE DIAGNOSIS OF PANCREATIC DISEASE
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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 340-1 and Fig. 340-1. At some institutions, pancreatic function tests are available and performed if the diagnosis of chronic pancreatic disease remains a possibility after noninvasive tests (ultrasound, computed tomography [CT], magnetic resonance cholangiopancreatography [MRCP]) or invasive tests (endoscopic retrograde cholangiopancreatography [ERCP], ...