The mechanisms for this form of encephalitis are unknown. Various hypotheses have been advanced but the one that is deemed most likely is that it represents an autoimmune process following vaccination. Midbrain, cerebral and medullary lesions have been observed, and in 1/5th of cases myelitis is predominant. Increases in CSF pressure, CSF lymphocytosis, and increases in CSF protein content all represent non-specific findings.
Approximately 25% of all cases were fatal and 25% of all survivors have had some residual neurologic defect, ranging from a convulsive disorder to profound neurologic deficit.
