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West Nile paralysis sometimes unaccompanied by traditional symptoms, WSU research finds. 

Paralysis due to West Nile virus is not always accompanied by signs of infection, according to a Wayne State University School of Medicine report to be presented at the American Neurological Association annual meeting on Tuesday in New York City.

Recent reports have described limb paralysis or a “polio-like” condition due to West Nile virus infection in otherwise healthy adults. These patients all had obvious symptoms of infection, such as fevers, headaches, vomiting, or confusion, before limb weakness began to set in.

Researchers at WSU School of Medicine now report that doctors need to be alert to cases of sudden paralysis that are not preceded by obvious signs of infection. Dr. Richard Lewis, WSU associate chair of neurology, has confirmed four cases (with several more pending) of West Nile-induced paralysis in one or more limbs, in which the patients reported, at most, mild flu-like symptoms leading up to the paralysis. The patients were between the ages of 24 and 68.

"I wouldn't want to alarm the public unnecessarily, particularly since there is little that they can do except avoid mosquito bites. However, I think it is important for people to realize that the infection is not confined to the elderly or immunosuppressed, although it may take a different form in younger people," said Dr. Richard A. Lewis, M.D., the paper’s lead author and a specialist in neuromuscular disorders.

The report is intended to make physicians, particularly neurologists, emergency physicians, family physicians and internists, aware of the unusual way these patients may manifest this viral disease, Dr. Lewis said.

Officials in Michigan have confirmed more than 400 infections by West Nile virus and more than 20 deaths. There are probably many more, but the state health department has had difficulty keeping up with the number of samples sent in for study.

There have been previous reports of paralysis due to West Nile virus, but these were primarily in the elderly or people who were already immunologically weakened from other illnesses, and the paralysis was always associated with other symptoms of infection, such as fever, headaches, nausea, vomiting, and confusion.

Since August, neurologists at Wayne State have encountered patients who over a period of hours had become paralyzed in one or two limbs, without pain, fever, or numbness. Some of these patients were not confused and had no signs of a brain infection (encephalitis), although they all had experienced some mild flu-like symptoms a week before their paralysis.

In the laboratory tests that have been completed – four to date – all have confirmed that these patients had contracted West Nile virus. Tests results are pending in several other cases.

"These patients didn't have many signs to suggest an infectious process, and it would be easy to not consider West Nile virus unless the unique features of the presentation were recognized," Dr. Lewis said.

The physicians still do not know the long-term effects of this particular manifestation of West Nile virus. On the one hand, none of the patients has died, but on the other, none has recovered from the paralysis.

How West Nile causes the paralysis is not clear, but the researchers speculate that nerve fibers or nerve cells in or near the spinal cord may be the targets of the virus.

"There is a lot we don't know about this infection and it will be important for us to learn as much about this as we can. Luckily, at least in Michigan, the season for mosquitoes is passing, hopefully giving us time to come up with some answers," Dr. Lewis said.

With more than 1,000 medical students, WSU is among the nation’s largest medical schools. Together with its clinical partner, the Wayne State University Physician Group, the school is a leader in patient care and medical research in a number of areas, including cancer, genetics, the neurosciences and women’s and children's health.