PSC is suspected from the pattern of liver tests and confirmed by imaging. No single test settles the diagnosis on its own: the cholangiogram supplies the defining findings, while the clinical, biochemical and serological picture and the exclusion of other causes decide whether those findings mean PSC.
The diagnostic approach
The work-up starts in a patient who has cholestatic signs or symptoms — typically a raised alkaline phosphatase — and who is negative for AMA (antimitochondrial antibody), the marker that points to primary biliary cholangitis. An ultrasound is performed first, to rule out acute cholecystitis or other conditions that ultrasound can diagnose. If those requirements are met, an MRCP (magnetic resonance cholangiopancreatography, the non-invasive MRI study of the bile ducts) is performed.
There are no standardised diagnostic criteria for PSC. The approach generally taken is to combine classical cholangiographic findings with the clinical, biochemical, serological and histological picture, after excluding the secondary causes of sclerosing cholangitis. Secondary causes are the reason the word primary exists: a known injury to the ducts, rather than an unexplained one, changes the diagnosis.
What MRCP shows
MRCP, the first-line investigation for PSC, shows multifocal strictures located between segments of normal or near-normal calibre and dilated segments. A stricture is defined as an internal diameter of less than 1 mm for the hepatic duct, less than 1.5 mm for the common bile duct, and less than 2 mm at the bifurcation points.
MRCP has high sensitivity and specificity for PSC, but it is not perfect. If the result is negative or equivocal while suspicion remains high, ERCP (endoscopic retrograde cholangiopancreatography) is performed, because it can image the ducts directly and allow a tissue sample to be taken.
Who should be tested
Two groups deserve testing even without obvious symptoms. MRCP is recommended in patients with IBD who have cholestatic biochemical findings, because their pre-test probability of PSC is high — the combination of bowel disease and a cholestatic liver test is not something to watch. In the other direction, colonoscopy with biopsy is recommended in all patients with PSC, to rule out IBD, since the two conditions so often travel together.