To the Editor: Based on the results of SPECT
imaging, Dr Marek and colleagues1 discussed
a possible "neuroprotective" effect of dopamine receptor agonists. Inspection
of Figure 3 and the data in Table 2, however, suggest that the rates of decline
of DAT binding in levodopa and pramipexole groups from 22 to 46 months have
identical slopes. We found that 2-way analysis of variance, using the data
from Table 2, demonstrated significant differences between the levodopa and
pramipexole treatment groups but no interactions between time and treatment,
confirming lack of difference in the rates of decline of DAT binding between
the 2 groups. This is consistent with the identical clinical ratings of both
groups at 46 months and argues against differential disease-modifying effect
of the treatment arms. A true neuroprotective effect should produce diverging
rates of decline with the effective treatment exhibiting slower rate of progression.2 In the study of Marek et al,1
only the slopes of DAT binding between initial scans (unmedicated baseline)
and the second scan (first onmedication scan) are significantly different.
This could be attributable to differential effects of levodopa and pramipexole
on DAT binding.
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