Subtypes of Alzheimer's atrophy on MRI associate with different rates of subsequent cognitive decline

An interesting study from Risacher et al splits ADNI participants into three subtypes of Alzheimer's, based on whether their baseline atrophy was more severe in the hippocampus and/or cortex. These groups were previously defined based on where in the brain pathologic tau deposits are predominant on postmortem exam, but the authors adapted them to the MRI level. Here were their definitions:

• Hippocampal sparing (HpSpMRI) = Hippocampal volume:Cortical volume ratio > 75th percentile, Hippocampal volume > median, Cortical volume < median. (n = 33)

• Limbic predominant (LPMRI) = Hippocampal volume:Cortical volume ratio < 25th percentile, Hippocampal volume < median, Cortical volume > median.  (n = 38)

• Typical AD (tADMRI) = all other participants (n = 158)

For participants who had 24 month longitudinal data, they found that the hippocampal sparing subtype had the worst progression of cognitive decline, despite a similar baseline cognition profile:

Figure 2C from PMID: 29070667