December 4, 2002
Contact: Dianne Needham, Warren Grant Magnuson Clinical Center Communications Office, (301) 496-2563
BETHESDA, Md. Extensive changes in deep brain tissue or gray matter caused by West Nile Virus (WNV) encephalitis have been observed in magnetic resonance images (MRI)for the first time. That finding is described in a case report from scientists at the Warren Grant Magnuson Clinical Center, National Institutes of Health (NIH).
Using serial magnetic resonance imaging physician-researchers monitored West Nile disease progression in a 55-year white male. MRI was conducted 6 times over approximately five weeks (days 5, 8, 11, 18, 23, and 37). Deep gray matter involvement in WNV encephalitis was not found until day 11 of fever day 7 of neurological symptoms. "The serial images enabled us to follow the disease progression over a protracted timeframe. This aids us in understanding the impact on brain function," said John A. Butman, M.D., Ph.D., Staff Neuroradiologist, Diagnostic Radiology Department, NIH Clinical Center.
Dr. Butman and co-authors Juan C. Gea-Banacloche, M.D., Michael W. Haley, M.D., Paul A. Nyquist, M.D., and Avi S. Retter, M.D. presented the case report at the 88th Scientific Assembly and Annual Meeting of the Radiological Society of North America held Dec. 1-6, in Chicago.
According to the case report, the MR findings lag behind the clinical picture of WNV encephalitis, indicating that a patient's condition can be much worse than initial MR findings may suggest. "Progression of disease may be seen on MR examination between days 7 and 14," said Dr. Butman.
The researchers noted that the sites of brain involvement with WNV encephalitis have a high overlap with viruses in the same family, and produce similar symptoms. "St. Louis encephalitis is like WNV encephalitis in that it is very unusual to have early MRI findings, whereas Japanese encephalitis often has early MR findings," said Dr. Butman.
The most serious consequences of WNV, which is typically asymptomatic or accompanied by mild, flu-like symptoms that last a few days and do not appear to pose any long-term health threat, are encephalitis and meningitis. However, explained Dr. Butman, an estimated 1 in 150 WNV cases become clinically apparent with neurological symptoms. Of those cases approximately 50 percent develop into encephalitis.
Most often found in Africa, Asia and the Middle East WNV has been in the U. S. since mid-1999 or earlier, according to the Centers for Disease Control. In a 1999 New York City WNV outbreak, MRI documented evidence of meningitis but did not observe infection of the brain tissue. "It is likely that encephalitis was present but undetected visually by MRI," said Dr. Butman.
A normal MRI does not exclude WNV encephalitis, Dr. Butman pointed out."This report reinforces that there can be very subtle findings of the disease early on in WNV. The absence of MRI visible disease does not indicate disease status," he said. He added that a negative initial MRI is to be expected with WNV encephalitis and that there may be fairly extensive disease present in the brain despite a negative MRI. "The consequences of what was likely there from the start may be seen in a week or two."
The case report's results, emphasized Dr. Butman, do not render the initial MRI irrelevant. While physicians wait for spinal fluid pathology results, MR findings can be used to rule out the presence of other neurological disease with overlapping symptoms. "This case gives us the knowledge that MRI is not particularly sensitive to the type of infection caused by WNV encephalitis. Consequently, fairly extensive progression occurs before the disease becomes visible," he said.