Effect of age at onset on progression and mortality in Parkinson's disease.

We examined longitudinal disability scores in 54 patients with Parkinson's disease followed for 6 years at UCLA. We sorted data into 3 groups based on age at onset of symptoms: group A, onset under 50 years; group B, 50 to 59 years; group C, 60 years or older. There were no significant differences between groups initially. All 3 groups improved dramatically when levodopa was given, but group A showed significantly less disability in years 4, 5, and 6 than did group C. The groups did not differ with respect to side effects. To determine if age at onset affected mortality, we sorted records from 4 geographically diverse centers into the same 3 groups. Results on 359 patients followed for 3,314 person-years, covering a period of 17 years after onset of symptoms, showed that group A had the most favorable observed-to-expected mortality ratio, 1.82, compared with 2.17 and 2.20 for groups B and C respectively, but the difference was not statistically significant. Results from the disability analyses indicate that patients with onset of Parkinson's disease under 50 years of age may have a more favorable prognosis than those whose symptoms begin in later years.