Is progression in postencephalitic Parkinson's disease late and age-related?

Follow-up data are presented of ten patients with autopsy-proven postencephalitic Parkinson's syndrome (PEP) (mean age at death: 56.0 years) with regard to motor and psychic deterioration over a period of institutional observation between 3 and 30 years. Four patients showed deterioration of their Hoehn-Yahr score of at least one grade. These patients did not differ statistically with respect to age of occurrence of lethargic encephalitis, interval to PEP, age at start of PEP, duration of survival with PEP, and age at death. Motor deterioration in these patients seems to be attributed more to inherent disease progression, rather than to an age-related process. Clinical and pathological evidence for this conclusion is presented.