Dr. James J. Sejvar responds:

It can be tempting for a physician to try to find an explanation for a patient's illness in the absence of a firm diagnosis. I think it's unlikely, however, that a prior history of influenza infection would be the source of your mother's current illness.

Influenza can be associated with various neurologic problems: encephalopathy (a state of confusion), seizures, neuropathy, as well as others. These complications most frequently occur in children, although cases of neurologic illness associated with adult influenza certainly occur. In most cases, the relationship of influenza-virus infection to these neurologic illnesses is not well understood: We don't know how—or in some cases if—the influenza virus causes the neurologic disease.

Progressive neurologic disease due to influenza-virus infection would be particularly unusual. However, during the 1918 influenza pandemic, there was also an outbreak of a strange illness known as encephalitis lethargica, in which people developed neurologic problems including, in some cases, features of Parkinsonism—problems with balance, slow movements, and facial masking [a symptom in which facial muscles become immobilized]. But, the relationship between the influenza pandemic and the outbreak of encephalitis lethargica remains unclear, and they were probably unrelated. People who recover from a severe case of influenza sometimes also develop features of Parkinsonism, but these generally occur shortly after the infection rather than appearing as a progressive disorder.

Although we probably cannot completely exclude some relationship between your mother's current illness and her influenza infection, it would be very important for her physicians to make sure that they are exploring other more likely reasons for her illness.