Neuropsychological Test Performance in Parkinsonism Without Dopaminergic Deficiency on [123I]-FP-CIT SPECT Imaging

To examine neuropsychological test performance among individuals clinically diagnosed with Parkinson's disease (PD) without evidence of dopaminergic deficiency on [123]I-CIT single photon emission computed tomography imaging.

Data were obtained from the Parkinson's Progression Marker Initiative. The sample included 59 participants with scans without evidence of dopaminergic deficiency (SWEDD), 412 with PD, and 114 healthy controls (HC). Tests included Judgment of Line Orientation, Letter-Number Sequencing, Symbol Digit Modalities, Hopkins Verbal Learning Test-Revised, and Letter and Category Fluency. Multivariate analysis of variance was used to compare standardized scores between the groups.

There was a statistically significant difference in performances between the groups, F(14,1155)=5.04; p<.001; partial η2=.058. Pairwise comparisons revealed significant differences in Category Fluency between SWEDD (M=0.22; SD=1.08) and HC (M=0.86; SD=1.15) and in Symbol Digit Modalities Test performance between SWEDD (M=45.09; SD=11.54) and HC (M=51.75; SD=9.79). No significant differences between SWEDD and PD were found. Using established criteria, approximately one in four participants in the SWEDD and PD groups met criteria for mild cognitive impairment (MCI).

Individuals with SWEDD demonstrate significantly worse mental processing speed and semantic fluency than HC. The neuropsychological test performances and rates of MCI were similar between the SWEDD group and PD groups, which may reflect a common pathology outside of the nigrostriatal pathway. (JINS, 2018, 24, 646-651).