Brain perfusion abnormalities in Alzheimer's disease: comparison between patients with focal temporal lobe dysfunction and patients with diffuse cognitive impairment

Objectives-Patients with Alzheimer's disease (AD) showing a selective impai rment of episodic and semantic memory have recently been classified as affe cted by focal temporal lobe dysfunction (FTLD) and considered as a distinct subgroup of patients affected by a particular form of AD. The aim was to c ompare the cerebral perfusion of patients with AD with FTLD and patients wi th AD with the more typical profile of diffuse cognitive impairment (dAD). Methods-Ten patients with AD with FTLD, 14 patients with AD with dAD, and 1 2 normal controls were studied. All the 24 patients with AD underwent a com plete neuropsychological assessment. SPECT examination with [Tc-99m]-HMPAO, using a four head brain dedicated tomograph, was performed in patients and controls. Tracer uptake was quantified in 27 regions of interest (ROIs), i ncluding lateral and mesial temporal areas. Mean counts in the 27 ROIs of c ontrols, patients with FTLD and those with dAD were compared using an ANOVA for repeated measures with Bonferroni's correction. A logistic regression analysis, followed by a receiver operating characteristic (ROC) analysis, w as also applied to select SPECT patterns which significantly differentiated patients with FTLD and those with dAD. Results-Two scintigraphic patterns of abnormalities, shaping a double disso ciation between the FTLD and dAD groups, emerged: a bilateral mesial tempor al hypoperfusion, characteristic of FTLD and a posterior parietal (and temp oral parietal) hypoperfusion characteristic of patients with dAD. Conclusions-These scintigraphic findings provide further support to the hyp othesis that FTLD is not a mere stage but a distinct anatomoclinical form o f AD. The combination of neuropsychological tests and [Tc-99m]-HMPAO SPECT may be very useful in identifying patients with FTLD from the wider group o f patients with dAD. This issue is particularly worthwhile, as there is inc reasing evidence that patients with FTLD have a slower rate of cognitive de cline.