Objectives: To measure the rate of progression in striatal [18F]dopa metabolism in a large group (n=32) of patients with Parkinson's disease, to estimate the average duration of preclinical period, and to examine the influence of the PET method on the assessment of rate of progression and preclinical period.
Methods: Thirty two patients with Parkinson's disease (mean age 58 (SD 13) years, mean duration 39 (SD 33) months) were assessed with [18F]dopa PET and UPDRS scoring on two occasions a mean of 18 (SD 6) months apart. PET data were sampled with separate caudate and putamen and total striatal regions of interest, and both graphical (Ki) and ratio methods of analysis.
Results: The mean annual rate of deterioration in [18F]dopa uptake varied according to structure and method of analysis, with putamen Ki showing the most rapid mean rate of progression (4.7% of normal mean per year). The group showed a significant deterioration (p<0.0004, paired two tailed t test) in UPDRS and in the putamen (p=0.008) and total striatal (p=0.012) [18F]dopa uptake measured using a graphical analysis, but no significant change in caudate or putamen uptake measured by a ratio approach. A study of sensitivity confirmed that putamen Ki was the most sensitive measure of disease progression, caudate ratio the least. Symptom onset in Parkinson's disease was estimated at a mean putamen [18F]dopa uptake (Ki) of 75% of normal and a mean caudate [18F]dopa uptake (Ki) of 91% of normal.
Conclusions: Estimation of mean rate of progression varies according to the sensitivity of a functional imaging method to clinical severity. Sensitivity and reproducibility of method must be considered when designing studies of disease progression and neuroprotection. The mean preclinical period in Parkinson's disease is unlikely to be longer than seven years.