A rare progressive disorder characterized by inflammation, thickening, and abnormal formation of fibrous tissue (fibrosis) within the passages that carry bile from the liver (bile ducts). This often results in the obstruction or interruption of bile flow from the liver (cholestasis). Symptoms associated with primary sclerosing cholangitis include fatigue and itching (pruritis), followed by yellowing of the skin, mucous membranes, and whites of the eyes (jaundice). In addition, affected individuals may have dark urine, light-colored stools, abdominal pain, and/or nausea. In some cases, the liver may also become abnormally enlarged (hepatomegaly). The exact cause of primary sclerosing cholangitis is not known.