Why is Alzheimer disease confused with other dementias?

Alzheimer disease (AD) is the most common cause of dementia. The cardinal manifestation of AD is progressive loss of memory. However, there are some nonamnestic presentations of AD, also called atypical AD. Symptoms of AD can sometimes start suddenly. In the presence of atypical symptoms or sudden onset, it may be difficult to distinguish AD from other dementias. We would like to discuss the confusing features of atypical AD that mimic other dementias. In this review, the literature associated with confusing features of AD, suggesting other dementia syndromes, is reviewed. In addition, a case of semantic dementia (SD) with the complaint of forgetfulness previously diagnosed as AD is presented together with clinical and radiological clues of the differential diagnosis of dementia syndromes. As in our representative SD case, a careful clinical history, a detailed mental evaluation, and neuroimaging will overcome this difficulty in diagnosis.