Differing patterns of temporal atrophy in Alzheimer's disease and semantic dementia.

OBJECTIVE: To characterize and quantify the patterns of temporal lobe atrophy in AD vs semantic dementia and to relate the findings to the cognitive profiles. Medial temporal lobe atrophy is well described in AD. In temporal variant frontotemporal dementia (semantic dementia), clinical studies suggest polar and inferolateral temporal atrophy with hippocampal sparing, but quantification is largely lacking. METHODS: A volumetric method for quantifying multiple temporal structures was applied to 26 patients with probable AD, 18 patients with semantic dementia, and 21 matched control subjects. RESULTS: The authors confirmed the expected bilateral hippocampal atrophy in AD relative to controls, with involvement of the amygdala bilaterally and the right parahippocampal gyrus. Contrary to expectations, patients with semantic dementia had asymmetric hippocampal atrophy, more extensive than AD on the left. As predicted, the semantic dementia group showed more severe involvement of the temporal pole bilaterally and the left amygdala, parahippocampal gyrus (including the entorhinal cortex), fusiform gyrus, and the inferior and middle temporal gyri. Performance on semantic association tasks correlated with the size of the left fusiform gyrus, whereas naming appeared to depend upon a wider left temporal network. Episodic memory measures, with the exception of recognition memory for faces, did not correlate with temporal measures. CONCLUSIONS: Hippocampal atrophy is not specific for AD but is also seen in semantic dementia. Distinguishing the patients with semantic dementia was the severe global but asymmetric (left > right) atrophy of the amygdala, temporal pole, and fusiform and inferolateral temporal gyri. These findings have implications for diagnosis and understanding of the cognitive deficits in AD and semantic dementia.

Early detection and differential diagnosis of Alzheimer's disease and depression with neuropsychological tasks.

The development of novel treatments for Alzheimer's disease (AD), aimed at ameliorating symptoms and modifying disease processes, increases the need for early diagnosis. Neuropsychological deficits such as poor episodic memory are a consistent feature of early-in-the-course AD, but they overlap with the cognitive impairments in other disorders such as depression, making differential diagnosis difficult. Computerised and traditional tests of memory, attention and executive function were given to four subject groups: mild AD (n = 26); questionable dementia (QD; n = 43); major depression (n = 37) and healthy controls (n = 39). A visuo-spatial associative learning test accurately distinguished AD from depressed/control subjects and revealed an apparent sub-group of QD patients who performed like AD patients. QD patients' performance correlated with the degree of subsequent global cognitive decline. Elements of contextual and cued recall may account for the task's sensitivity and specificity for AD.

No right to speak? The relationship between object naming and semantic impairment: neuropsychological evidence and a computational model.

The processes required for object naming were addressed in a study of patients with semantic dementia (a selective decline of semantic memory resulting from progressive temporal lobe atrophy) and in a computational model of single-word production. Although all patients with semantic dementia are impaired in both single-word production and comprehension, previous reports had indicated two different patterns: (a) a parallel decline in accuracy of naming and comprehension, with frequent semantic naming errors, suggesting a purely semantic basis for the anomia and (b) a dramatic progressive anomia without commensurate decline in comprehension, which might suggest a mainly postsemantic source of the anomia. Longitudinal data for 16 patients with semantic dementia reflected these two profiles, but with the following additional important specifications: (1) despite a few relatively extreme versions of one or other profile, the full set of cases formed a continuum in the extent of anomia for a given degree of degraded comprehension; (2) the degree of disparity between these two abilities was associated with relative asymmetry in laterality of atrophy: a parallel decline in the two measures characterized patients with greater right- than left-temporal atrophy, while disproportionate anomia occurred with a predominance of atrophy in the left-temporal lobe. In an implemented computational model of naming, semantic representations were distributed across simulated left- and right-temporal regions, but the semantic units on the left were more strongly connected to left-lateralized phonological representations. Asymmetric damage to semantic units reproduced the longitudinal patient profiles of naming relative to comprehension, plus additional characteristics of the patients' naming performance. On the basis of both the neuropsychological and computational evidence, we propose that semantic impairment alone can account for the full range of word production deficits described here.

Semantic knowledge and episodic memory for faces in semantic dementia.

Previous studies have documented poor recognition memory for faces in patients with semantic dementia. Preserved face recognition memory was found in this study, however, so long as atrophy was confined predominantly to the left temporal lobe. Patients with structural damage to the right temporal lobe were typically impaired, with the status of the hippocampus and parahippocampal gyrus (including the perirhinal cortex) on the right being critical. Two single-case studies of patients with predominantly left temporal lobe pathology confirmed good recognition memory for famous faces, even if semantic knowledge about the celebrities depicted was severely degraded. An effect of semantic knowledge on recognition memory became apparent only when perceptually different photographs of the famous people were used at study and test. These results support the view that new episodic learning typically draws on information from both perceptual and semantic systems.

Temporal lobe rating scale: application to Alzheimer's disease and frontotemporal dementia.

OBJECTIVES: Temporal lobe atrophy as assessed by MRI can be measured in several ways. Volumetric measurements are quantitative but very time consuming and require extensive training to perform, so are not easily transferable to clinical practice. Visual rating scales, by contrast, are quick and widely applicable. Although medial temporal lobe atrophy is well described in Alzheimer's disease (AD), it is uncertain how early these changes can be detected and whether they discriminate AD from other neurodegenerative diseases, most notably frontotemporal dementia (FTD). The objectives were (1) to develop a widely applicable temporal lobe rating scale, and (2) to characterise and quantify the patterns of temporal lobe atrophy in AD versus temporal and frontal variants of FTD. METHODS: The temporal lobe assessments were made using an established hippocampal rating scale extended to incorporate additional temporal regions. This was firstly validated with volumetric analysis and then applied to 30 probable AD, 30 FTD (consisting of 17 temporal variant (semantic dementia) and 13 frontal variant) and 18 control coronal MRI images. RESULTS: Bilateral hippocampal atrophy was found in 50% of the patients with AD. Contrary to expectations, patients with semantic dementia also had hippocampal atrophy, which for the left side exceeded that seen in AD; other regions (temporal pole, parahippocampal gyrus, and lateral temporal lobe), spared in AD, were severely atrophied in this group. The patients with frontal variant FTD occupied an intermediate position and were largely indistinguishable from AD. CONCLUSIONS: Hippocampal atrophy is, therefore, not specific for AD. Semantic dementia can be distinguished from AD, by the presence of severe bilateral atrophy of the temporal pole, parahippocampal and lateral regions. These findings have implications for the differential diagnosis of dementias.

Rasmussen's syndrome in a 54 year old female: more support for an adult variant.

Rasmussen's syndrome, a syndrome of chronic focal encephalitis, is usually considered to be a disease of childhood. Typical features include intractable focal seizures and progressive unilateral neurological deficits with radiological evidence of focal cortical atrophy. This report documents the case of the oldest patient yet described in the literature with Rasmussen's syndrome. Magnetic resonance imaging revealed gadolinium enhancing tissue, not previously described in this condition.

Atypical and typical presentations of Alzheimer's disease: a clinical, neuropsychological, neuroimaging and pathological study of 13 cases.

There has been increasing awareness that some slowly progressive focal cortical syndromes can be the presenting features of Alzheimer's disease, but pathological evidence has been sparse. This clinico-pathological series presents our experience with pathologically proven atypical as well as typical Alzheimer's disease presentations. We report and compare four patterns of presentation: a typical pattern with initial amnesic syndrome (n = 4 cases), progressive visual dysfunction (n = 1), progressive biparietal syndrome (n = 2) and progressive aphasia (n = 6). The aphasic presentations include both fluent and non-fluent aphasic syndromes. The neuropsychological profiles and neuroimaging clearly reflect the presenting clinical features, and show a close relationship to the distribution of pathology in these cases. Of note was the sparing of medial temporal structures (hippocampus and/or entorhinal cortex) in several aphasic cases and the severe occipito-parietal involvement in those with prominent visuospatial disorders at presentation. Our data demonstrate the wide spectrum of Alzheimer's disease presentations. The recognition of atypical presentations of Alzheimer's disease is important when attempting to make an early accurate pre-morbid diagnosis of neurodegenerative disease.

Francis Galton: and eugenics today.

Eugenics can be defined as the use of science applied to the qualitative and quantitative improvement of the human genome. The subject was initiated by Francis Galton with considerable support from Charles Darwin in the latter half of the 19th century. Its scope has increased enormously since the recent revolution in molecular genetics. Genetic files can be easily obtained for individuals either antenatally or at birth; somatic gene therapy has been introduced for some rare inborn errors of metabolism; and gene manipulation of human germ-line cells will no doubt occur in the near future to generate organs for transplantation. The past history of eugenics has been appalling, with gross abuses in the USA between 1931 and 1945 when compulsory sterilization was practised; and in Germany between 1933 and 1945 when mass extermination and compulsory sterilization were performed. To prevent such abuses in the future statutory bodies, such as a genetics commission, should be established to provide guidance and rules of conduct for use of the new information and technologies as applied to the human genome.

Francis Galton: his approach to polygenic disease.

Gregor Mendel is considered to be the founding father of modern genetics, and his laws of inheritance have led to the successful analysis of rare monogenic diseases such as cystic fibrosis, Duchenne muscular dystrophy, familial hypercholesterolaemia, and many others. Francis Galton chose multifactorial inheritance as his starting point, and his methods of analysis have withstood the test of time. He used detailed family records to study the inherited tendency of complex traits between parents and offspring, and between identical and non-identical twins to refine the analysis, and devised new statistics to attempt to measure the extent of inheritance. For all these reasons, he can be considered the founding father of quantitative genetics.