It has been generally recognized that postencephalitic mental disturbances in children are always preceded by some physical signs. Behavior disturbances, recognized as due to the encephalitis, because of an acute onset following a typical epidemic encephalitis history, are nearly always accompanied by some neurologic findings in the form of pupillary changes, facial paresis, muscle stiffness, etc. These behavior disturbances have been shown to be typical of an organic brain disease quite unlike the usual behavior disturbances in children. It has been demonstrated1 that there is little or no correlation between the severity of the mental disturbance and the physical symptoms; children with slight mental disturbance may have extreme physical findings and vice versa.
Originally the behavior of a child was pronounced postencephalitic when the following three conditions were fulfilled: (1) a sudden change in personality, (2) physical evidence of postencephalitis and (3) a history of acute epidemic encephalitis. Later
BEVERLY BI, SHERMAN M. POSTENCEPHALITIC BEHAVIOR DISTURBANCE WITHOUT PHYSICAL SIGNS. Am J Dis Child. 1924;27(6):565-568. doi:10.1001/archpedi.1924.01920120027004