Antibody Index Test May Aid PML Diagnosis on Natalizumab

Sue Hughes

COPENHAGEN, Denmark — A new test that compares JC virus (JCV) antibody levels in cerebrospinal fluid (CSF) with those in serum might be a useful complementary tool in the diagnostic workup for progressive multifocal leukoencephalopathy (PML) in patients with multiple sclerosis (MS) treated with natalizumab (Tysabri, Biogen Idec), a new study suggests.

The study was presented by Clemens Warnke, MD, Heinrich Heine University, Düsseldorf, Germany, at the recent 29th Congress of the European Committee for Treatment and Research in Multiple Sclerosis (ECTRIMS). 

Dr. Warnke explained that PML caused by JCV can be difficult to diagnose because early symptoms can be mistaken for a relapse in MS.

“At present, JCV-DNA detection by polymerase chain reaction (PCR) in cerebrospinal fluid is used for diagnosis of PML. However, false-negatives often occur, leading to delayed diagnosis and poor patient outcome in some cases,” he said. “So we need more tests to allow earlier diagnosis.”

“Our main findings are when you have clinical suspicion of PML — changes in behavior, personality, and motor function untypical for MS in patients treated with natalizumab, we might suspect it to be PML,” he told Medscape Medical News.

He and his colleagues have proposed using the anti-JCV antibody specificity index (ASI-JCV) as an additional test for JCV DNA detection. This involves measuring the JCV antibody level in both serum and CSF and calculating the proportion of antibodies in CSF compared with serum.

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