We report 12 cases of primary sclerosing cholangitis (confirmed by cholangiography) in which the serum alkaline phosphatase activity was normal. The enzyme activity remained normal during follow-up in 7 cases and fluctuated in 5 cases (it returned to normal in 4). The presence of advanced histologic stage (fibrosis/cirrhosis) with marked cholangiographic changes in 4 patients establishes that cirrhotic-stage primary sclerosing cholangitis can occur without a concomitant increase in serum alkaline phosphatase activity. Therefore, primary sclerosing cholangitis may exist in an occult state without symptoms or increase in serum alkaline phosphatase activity. Our findings suggest that primary sclerosing cholangitis may be more prevalent than realized, especially in patients who have inflammatory bowel disease. A normal value for serum alkaline phosphatase activity should not preclude further investigation for primary sclerosing cholangitis in patients with inflammatory bowel disease when symptoms or signs suggest liver disease.
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