Introduction

Alzheimer's disease (AD) is the most common form of dementing illness in the elderly (Kokmen et al.,1993), but advances in molecular pathology over the past few decades have led to the identification of other common neurodegenerative disorders (Prusiner and Hsiao, 1994; Neary et al., 1998; McKhann et al., 2001; Boeve et al., 2003; Lippa et al., 2007; Murray et al., 2007). Patients with these non-Alzheimer dementia disorders frequently have similar subjective complaints as patients with AD, but atypical features in the evaluation of these cognitively impaired patients should alert the astute physician of an alternative non-AD diagnosis, including behavioral and language variants of frontotemporal dementia (Neary et al., 1998; McKhann et al., 2001), dementia with Lewy bodies (Lippa et al., 2007), vascular dementia, and other forms of less common neurological disorders, including Creutzfeldt–Jakob disease (Prusiner and Hsiao, 1994). The utility of imaging studies has been studied extensively in many of these disorders, and this chapter will focus on the group differences between disorders and highlight the role of structural and functional imaging in non-Alzheimer dementias. Disease-specific features unique to one type or one group of disorders are frequently congruent with the localization model of neurodegenerative disease based on prominent clinical deficits, but the majority of these studies lack the power to determine the positive and negative predictive values of disease-specific features at the group level when used on an individual patient basis, despite variable amount of anecdotal clinical evidence.