**4.1 Introduction**

Frontotemporal lobe degeneration (FTLD) is a cause of degenerative dementias that recent research suggests, in individuals younger than 65, is as common as AD. Frontotemporal dementia (FTD) is the most common example of such diseases, for which clinical and pathological criteria were proposed in 1994 by Brun and colleagues (Brun, et al., 1994). The disease is characterized by behavioral and personality changes that result from the frontotemporal involvement and include apathy, disinhibition, and often sever impairment of language production. In related conditions, such as semantic dementia and progressive non-fluent aphasia, language impairment can be the major symptom, and dementia the

Diagnosis of Dementia Using Nuclear Medicine Imaging Modalities 221

areas of reduced cerebral glucose metabolism should be considered when making a diagnosis as, despite its name, there are more widespread hemispheric defects in glucose metabolism that occur in FTD. For example, reduced glucose metabolism in the orbital gyrus, anterior cingulate gyrus, frontal cortices, anterior temporal cortices, hippocampus, subcortical structures, parietal region, sensorimotor cortex, and the cerebellar cortex, discussed by Ishii (Ishii, 2002), are consistent with the pathological features and *post-mortem* findings of FTD.

Corticobasal degeneration (CBD) is a progressive dementia in which patients have cognitive decline, significant dementia and unique motor symptoms such as akineto-rigid syndrome (Ishii, 2002). In FDG PET of CBD patients, there is a decrease in absolute glucose metabolism in several regions of the brain, and distinct asymmetry in glucose metabolism patterns that is characteristic of the condition. For example, Hirono and colleagues showed that CBD patients had greater glucose metabolic asymmetries in the lateral frontal, lateral temporal, central and lateral parietooccipital regions than did the corresponding healthy controls (Hirono, et al., 2001). In the same study it was reported that the most significant pathologic changes in CBD appear in the pre- and post-central gyri, and parietal association cortices. Moreover, the associated metabolic asymmetries in the pre- and post-central gyri, as well as the thalamus, were larger in CBD than AD allowing differentiation of these conditions using

Progressive supranuclear palsy (PSP) is a condition associated with Parkinsonism and dementia. Pathological changes are most common in the basal ganglia and brain stem, and features of this neurodegenerative condition include behavioral derangement and cognitive decline (Ishii, 2002). In FDG PET of PSP patients, glucose metabolism is reduced in the lateral and medial frontal lobes, caudate nucleus and midbrain, when compared to normal

When dementia results from many small strokes, it is known as vascular dementia. In contrast to other dementias, it is relatively straightforward to diagnose vascular dementia from clinical symptoms, and with MRI or CT. Typically therefore nuclear medicine imaging is not needed for patients with pure vascular dementia (Ishii, 2002). On occasion however, vascular dementia can be associated with AD pathology. In such cases, FDG PET can be employed to distinguish vascular dementia from the reduced glucose metabolism profile

In conclusion, the sophisticated array of radiopharmaceuticals that have been developed for imaging dementia using PET and SPECT scans is highlighted. Using such imaging techniques alone, or in combination with each other (and/or MRI, CT etc.), allows physicians to differentiate between related, and frequently clinically overlapping, disease entities with a high degree of diagnostic confidence. However, whilst [18F]FDG is readily

**5. Imaging of other dementias 5.1 Corticobasal degeneration** 

**5.2 Progressive supranuclear palsy** 

associated with AD (see Section 2.2).

**5.3 Vascular dementia** 

**6. Conclusion** 

controls (Blin, et al., 1990; Hosaka, et al., 2002).

FDG PET.

lesser symptom. In contrast to other dementias however, there is no (or less prominent) memory impairment associated with FTLD. Therefore, clinical differentiation from other diseases such as AD is usually relatively straightforward. The main difficulty associated with managing FTLD is that it is not typically diagnosed in its early stages because mild symptoms often go unnoticed, or are difficult to verify. To address this issue, FDG PET has been investigated as a possibility for diagnosing and staging the FTLD-related conditions by identifying areas of reduced glucose metabolism that are characteristic of these conditions.
