USMLE Step 1 Question 310

Question:

A 46-year-old female with a history of painful spasms of the fingers in the cold complains of 2 weeks of fatigue, pruritus, and abdominal pain. Her exam is notable for scleral icterus, right upper quadrant pain, and a liver span of 11cm. Her laboratory values are as follows:

AST: 110
ALT: 102
Alkaline Phosphatase: 256
Total Bilirubin: 2.8
Direct Bilirubin: 1.9

An abdominal ultrasound shows no obstruction. A liver biopsy is taken and shows destruction of small interlobar bile ducts.

What antibody test will likely be positive?

Correct Answer: C.  Anti-mitochondrial

This patient is suffering from primary biliary cirrhosis (PBC) which is most commonly diagnosed in women in their 4th and 5th decade. PBC is an autoimmune disease in which the intrahepatic bile ducts are affected. Anti-mitochondrial antibodies (option C) are commonly found. The fact that she has a history of an autoimmune disease (painful spasms of the fingers in the cold is typical for Raynaud’s phenomenon) raises suspicion for this diagnosis. The elevated bilirubin and alkaline phosphatase in the absence of evidence of gall stones or obstruction of the biliary tract on ultrasound makes PBC the most likely diagnosis in this case.

Anti-Scl 70 (choice A) is seen in systemic scleroderma, which typically presents with skin tightening or esophageal dysmotility when part of the CREST variant.

Anti-ds DNA (choice B) is a specific marker for SLE.

Anti-smooth muscle antibodies (Choice D) are a marker of autoimmune hepatitis which would be expected to further elevate the AST and ALT.

P-ANCA (choice E) is often seen in primary sclerosing cholangitis (PSC), and in a variety of vasculitis diseases including Churg-Strauss. PSC is more commonly seen in patients with underlying ulcerative colitis and more commonly in men.