Background: Numerous conventional magnetic resonance imaging (cMRI) parameters were
previously found to differentiate parkinsonian disorders with statistical significance,
but effect size has not been considered.Objectives: To quantify effect size of previously
identified cMRI parameters that differentiated parkinsonian disorders with statistical
significance.Method: A PubMed search limited to studies assessing cMRI parameters
in at least 2 of Parkinson's disease, progressive supranuclear palsy, multiple system
atrophy, and corticobasal degeneration/syndrome were selected. Either Cohen's d or
positive and negative likelihood (LR+/-) as well as diagnostic odds ratios (DORs)
were calculated as appropriate. cMRI parameter was considered useful if Cohen's d
> 1.94 (<20% overlap) or if LR+ > 10, LR- < 0.1, or DOR > 20.Results: Literature search
identified 8848 publications and 36 were included for analysis. Putaminal (Cohen's
d 2.07; DOR 23-infinity), pontine (DOR 32-infinity), and middle cerebellar peduncle
(Cohen's d 2.24; DOR infinity) abnormalities were most useful in differentiating multiple
system atrophy while reduced midbrain (Cohen's d 2.33-8.69; DOR infinity) and superior
cerebellar peduncle (Cohen's d 2.47; DOR 51-infinity) diameters separated progressive
supranuclear palsy. Corticobasal degeneration/syndrome does not have any distinguishing
cMRI features, but reduced midbrain diameter may help differentiate corticobasal degeneration/syndrome
from Parkinson's disease (DOR infinity). When LR- was calculated, all of these features
carried a value of <0.1.Conclusion: A number of cMRI features consistently demonstrated
large effect size in separating parkinsonian disorders. However, it is the presence
and not absence of these cMRI features that is most useful in patients with low to
moderate pretest probability.
