To assess the prognostic value of hippocampal subfield volumes in predicting future cognitive status in terms of Level I Mild Cognitive Impairment (MCI) criteria.

148 PD patients from the Parkinson’s Progression Markers Initiative (PPMI) were selected and their baseline 3D T1-weighted image was processed with FreeSurfer and the hippocampus subfields module. Individual subfield and total hippocampal volumes were extracted. ANCOVA models, correcting for age, sex, and total intracranial volume, were used to compare hippocampal volumetry between PD patients with and without Level I MCI at baseline as well as after 3 and 4 years of follow-up.

At baseline, PD MCI had lower total hippocampal volume (p=0.008) and lower volumes for the hippocampal subfields including the tail (p=0.014), subiculum (p=0.047), cornu ammonis (CA) 1 (p=0.030), presubiculum (p=0.011), molecular layer HP (0.016), molecular and granule cell layers of the dentate gyrus (0.044) and CA4 (p=0.039) compared to PD with normal cognition. Lower baseline CA1 volume was also associated with MCI status at year 4 (p=0.035). When excluding the 22 patients with MCI at baseline, lower baseline total hippocampal volume and tail volume were associated with conversion to MCI at year 3 (p=0.047 and p=0.022, respectively).

Our findings suggest that total hippocampal and hippocampal subfield volumes may reflect pathology contributing to cognitive impairment in PD.  Low total hippocampal, hippocampal tail, and CA1 volume at baseline significantly predict future cognitive impairment in PD.