Diagnosis

The diagnosis of chronic pancreatitis is rather easy in patients with big duct disease and quite challenging in patients with small duct disease. Table 139-2 lists diagnostic tests that are carried out worldwide in the examination of patients with chronic pancreatitis. Tests of function usually precede tests of structure in regard to sensitivity. The most sensitive and most specific tests are at the top of each column with the least sensitive and specific at the bottom. In 2004, the most appropriate way of detecting whether or not chronic pancreatitis is present is a combination of a secretin hormone stimulation test and endoscopic ultrasonography

(EUS).In big duct disease, just about any test chosen will be abnormal. In our experience, we have used a serum trypsino-gen as a first line test in patients who appear to have severe pancreatic insufficiency (PI) and present with malabsorption/maldigestion. That test is now commercially available from general diagnostic laboratories. In our laboratory, the normal values are 29 to 58 ng/mL. Patients with chronic pancreatitis of a mild to moderate degree have values of 20 to 28 ng/mL; patients with values < 20 ng/mL have severe PI and this value usually correlates well with the presence of steatorrhea. A new test that has been introduced into the United States and is now US Food and Drug Administration (FDA)-approved is fecal elastase. This is a stool determination from an aliquot of stool, not a quantitative collection, and is measured by a radioimmunoassay of human fecal elastase. Normal values are > 200 ^g/g of stool. A value < 200 ^g/g but > 100 ^g/g usually reflects mild to moderate chronic pancreatitis. A value < 100 ^g/g is severe PI and correlates well with an abnormal fecal fat excretion or steatorrhea. These function tests reflect severe damage and often confirm the abnormalities found on computed tomography (CT) or magnetic resonance imaging (MRI). In patients with small duct disease who present largely just with pain and do not have maldigestion, those function tests just mentioned are often normal. Indeed in up to 40% of patients with small duct chronic pancreatitis, radiographic tests including CT, MRI, magnetic resonance cholangiography (MRCP) and endoscopic retrograde cholangiography (ERCP) may be normal. It is those patients with small duct disease that have radiographic negative findings that are the real challenge, particularly if the secretin hormone stimulation test is not available. Patients suspected of having small duct chronic pancreatitis should be referred to a center that is proficient in performing these tests. When compared against any radiographic test or function test as listed in Table 139-2, the secretin hormone stimulation test has consistently been found to be more sensitive and more specific. The secretin test has been evaluated against histology in over 100 patients from Japan. In this study, the bicarbonate concentration of pancreatic secretion was the most accurate parameter; ERCP was 60% as accurate as the bicarbonate concentration (Hayakawa et al, 1992).

TABLE 139-2. Diagnostic Tests for Chronic Pancreatitis

Tests of Function Tests of Structure

Secretin Test EUS

Fecal Elastase ERCP

Serum Trypsinogen CT

Fecal Chymotrypsin MRI/MRCP

Fecal Fat US KUB

*Editor's Note: Interestingly, two mutations in NOD 2/CARD 16 gene increase the risk of Crohn's disease 20- to 40-fold.

CT = computed tomography; ERCP = endoscopic retrograde cholangiography; EUS = endoscopic ultrasound; MRCP = magnetic resonance cholangiography; MRI = magnetic resonance imaging; US = ultrasound.

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