The main difference between the two being that Alzheimers is categorized by atrophy to both sides of the brain while semantic dementia is categorized by loss of brain tissue in the front portion of the left temporal lobe. With Alzheimers disease in particular, interactions with semantic memory produce different patterns in deficits between patients and categories over time which is caused by distorted representations in the brain. For example, in the initial onset of Alzheimers disease, patients have mild difficulty with the artifacts category. As the disease progresses, the category specific semantic deficits progress as well, and patients see a more concrete deficit with natural categories. In other words, the deficit tends to be worse with living things as opposed to non-living things. Diagnosis
SD patients generally have difficulty generating familiar words or recognizing familiar objects and faces. Clinical signs include fluent aphasia, anomia, impaired comprehension of word meaning, and associative visual agnosia (inability to match semantically related pictures or objects). As the disease progresses, behavioral and personality changes are often seen similar to those seen in frontotemporal dementia.SD patients perform poorly on tests of semantic knowledge. Published tests include both verbal and non-verbal tasks, e.g., The Warrington Concrete and Abstract Word Synonym Test, and The Pyramids and Palm Trees task. Testing also reveals deficits in picture naming (e.g. "dog" for a picture of a hippopotamus) and decreased category fluency. The question "What is a Stapler?"
SD was first described by Arnold Pick in 1904 and in modern times was characterized by Professor Elizabeth Warrington in 1975, but it was not given the name semantic dementia until 1989. The clinical and neuropsychological features, and their association with temporal lobe atrophy were described by Professor John Hodges and colleagues in 1992. Presentation
The defining characteristic of SD is decreased performance on tasks that require semantic memory. This includes difficulty with naming pictures and objects, single word comprehension, categorizing, and knowing uses and features of objects. SD patients also have difficulty with spontaneous speech creation, using words such as "this" or "things" where more specific and meaningful words can be used. Syntax is spared, and SD patients have the ability to discern syntactic violations and comprehend sentences with minimal lexical demands. SD patients have selectively worse concrete word knowledge and association, but retain knowledge and understanding of abstract words. SD patients are able to retain knowledge of numbers and music, but have more difficulty with concrete concepts with visual associations. Impairments of processing of phonemic structure and prosodic predictability have also been observed. Genetics
The majority of SD patients have ubiquitin-positive, TDP-43 positive, tau-negative inclusions, although other pathologies have been described more infrequently, namely tau-positive Picks disease and Alzheimers pathology. Of all the FTLD syndromes, SD is least likely to run in families and is usually sporadic. Alzheimers Disease and Semantic Dementia
Alzheimers disease is related to semantic dementia, which both have similar symptoms.