Differential Diagnosis for Deranged LFTs: Autoimmune Hepatitis vs. Azathioprine Use

When differentiating between autoimmune hepatitis and azathioprine use as the cause of deranged liver function tests (LFTs), it's crucial to consider various factors, including clinical presentation, laboratory findings, and the patient's medication history. Here's a structured approach to the differential diagnosis:

• Single Most Likely Diagnosis
  • Autoimmune hepatitis: This is a condition where the body's immune system attacks liver cells. The presence of elevated liver enzymes, along with specific autoantibodies (such as ANA, anti-smooth muscle antibodies), and a significant increase in IgG levels, supports this diagnosis. A liver biopsy may show interface hepatitis and plasma cell infiltration.
• Other Likely Diagnoses
  • Azathioprine-induced liver injury: Azathioprine, an immunosuppressive drug, can cause liver damage as a side effect. The pattern of liver enzyme elevation (e.g., more prominent elevation of alkaline phosphatase and gamma-glutamyl transferase) and the temporal relationship with azathioprine use are key factors. Withdrawal of the drug and monitoring for improvement can help confirm this diagnosis.
  • Drug-induced liver injury (DILI) from other medications: Other drugs the patient is taking could also cause liver injury, presenting similarly to azathioprine-induced liver injury. A thorough medication history and consideration of the drugs known to cause DILI are essential.
• Do Not Miss Diagnoses
  • Viral hepatitis: Acute or chronic infections with hepatitis viruses (A, B, C, D, E) can cause deranged LFTs. Missing a diagnosis of viral hepatitis could lead to delayed treatment and potentially severe consequences, including liver cirrhosis and hepatocellular carcinoma.
  • Wilson's disease: A genetic disorder leading to copper accumulation in the liver, which can cause liver damage and dysfunction. Although rare, missing this diagnosis can lead to severe and irreversible liver damage if not treated promptly.
• Rare Diagnoses
  • Primary biliary cholangitis (PBC): An autoimmune disease of the liver characterized by progressive destruction of the bile ducts within the liver. It's less common than autoimmune hepatitis but should be considered, especially in middle-aged women with cholestatic pattern of LFT derangement.
  • Primary sclerosing cholangitis (PSC): A chronic liver disease characterized by inflammation and scarring of the bile ducts, which can lead to liver damage. It's rare and often associated with inflammatory bowel disease, but it's a critical diagnosis not to miss due to its potential for severe complications.

Each of these diagnoses requires careful consideration of the patient's clinical presentation, laboratory results, and imaging studies to accurately determine the cause of deranged LFTs and initiate appropriate management.