Establishing neuropsychological similarities and differences between ypical amnestic AD (tAD) and with non-amnestic (naAD) syndromes may help improve the early diagnosis of naAD.

We compared neuropsychological measures of 41 patients meeting established criteria for biomarker-supported AD and having an age of onset of <65 years of age.  Based on the initial physician clinical evaluation, these 41 patients were divided into 22 tAD (14 male/8 female; mean years for age-58.4, disease duration-3.2, education-16.1 years) vs. 10 naAD (n=19; 9 lvPPA, 8 PCA, 2 BDV; 8 male/11 female; mean years for age-59.7, disease duration-4.0, education-16.2).  The two patient groups were of comparable severity on functional measures and had positron emission tomography or cerebrospinal fluid biomarker confirmation of their disease. We then analyzed neuropsychological differences between these two groups. 

The two AD groups did not differ in having memory impairment; however, using receiver operating characteristics, the naAD group was distinguishable from the tAD group by better delayed recall scores and worse memory registration.  The naAD patients were also worse on forward digit span, Trailmaking B time, uncued naming, and figure-ground discrimination.  Seventeen of the 19 naAD patients had this pattern on all 6 tests, and Trailmaking B added the highest specificity at 0.92. 

Both AD groups had memory difficulty, although more in encoding/storage in tAD and in registration in naAD.  The findings suggest neuropsychological measure for differentiation of naAD that include early impairment in mental control and executive abilities, uncued naming, memory registration, and mid-level visuospatial processing.  In sum, the naAD patients had additional frontal and parieto-occipital deficits, reflecting greater neocortical and less hippocampal involvement.