American Board of Internal Medicine (ABIM) Certification Practice Exam

What is a risk associated with elevated levels of JC virus antibodies in patients on natalizumab?

1. Increased risk of thromboembolism

2. Increased risk of progressive multifocal leukoencephalopathy (PML)

3. Increased risk of liver toxicity

4. Increased risk of seizures

The correct answer is: Increased risk of progressive multifocal leukoencephalopathy (PML)

Elevated levels of JC virus antibodies in patients who are on natalizumab are linked to an increased risk of progressive multifocal leukoencephalopathy (PML). PML is a serious brain infection caused by the reactivation of the JC virus, which is typically harmless in healthy individuals but can become pathogenic in immunocompromised patients. Natalizumab is a monoclonal antibody that is primarily used to treat multiple sclerosis and Crohn's disease. It works by blocking the movement of immune cells into the brain and spinal cord, thereby reducing inflammation. However, this immune suppression can increase the likelihood of opportunistic infections, including PML. The presence of JC virus antibodies indicates prior exposure to the virus, and a higher antibody titer signifies a greater risk of developing PML when patients are receiving immunosuppressive therapies like natalizumab. Monitoring JC virus antibody levels in patients on natalizumab is thus critical, as it allows healthcare providers to assess the risk of PML and to determine the necessity of regular surveillance or discontinuation of treatment if the risk becomes significant. This connection is important in clinical practice, as it helps to guide decisions and patient management strategies, especially considering the severity and potential fatal nature of PML.