Multimodal imaging in Alzheimer's disease: the relationship between MRI, SPECT, cognitive and pathological changes

Article Abstract:

In magnetic resonance imaging (MRI), protons (part of the nucleus of an atom) are exposed to rotating magnetic fields in the radio frequency range. When the frequency is stopped, the protons emit energy as they return to their former state. Computer analysis of this emitted energy portrays a spatial image of the distribution of specific elements (e.g., hydrogen). An important measure obtained during MRI is the time taken for the protons to return to a resting state after excitation (T-1). Using MRI, significant increases have been found in the white-matter T-1 of patients with Alzheimer's disease (AD). Another diagnostic procedure, single-photon emission computerized tomography (SPECT), in which variations in the density of brain tissue are measured from an X-ray source and detectors placed around the head, has demonstrated reduced cerebral blood flow (perfusion) in AD patients. To assess whether localized changes in white matter T-1 were related to cognitive deficits or to perfusion changes in the adjoining gray matter of AD patients, 21 right-handed patients with a clinical diagnosis of probable AD were evaluated with MRI. Thirteen of these patients were also evaluated with SPECT. All the patients were given a battery of cognitive tests. Significant relationships were found between localized perfusion reductions, T-1, and localized cognitive deficits. In general, the greater the T-1, the greater the perfusion reduction in adjoining gray matter. Significant relationships were also found between the T-1 of particular brain regions and performance on psychometric tests which tapped into those same regions. For instance, vocabulary test scores were significantly related to the T-1 of left hemisphere structures, which is in keeping with findings of vocabulary impairment in left-hemisphere disorder (of right-handed people). Relationships found between T-1 and pathological change may lead to a way of definitively diagnosing AD in living patients. To date, definitive diagnosis can only be accomplished by the post-mortem examination of white matter. (Consumer Summary produced by Reliance Medical Information, Inc.)

Magnetic resonance imaging, SPECT imaging, Single photon emission computed tomography

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Neurological soft signs in schizophrenia

Article Abstract:

Neurological hard signs refer to specific defects in central nervous system (CNS) nuclei tracts or nerves, while neurological soft signs (NSS) represent abnormalities on nonspecific tests, which do not indicate clearly identifiable CNS defects. NSS include phenomena such as: diminished dexterity, cortical sensory loss, choreiform (jerky) movements, and astereognosis (tactile amnesia). To explore the presence of NSS in schizophrenia, three groups of subjects were administered a standard neurological examination: the first included 58 hospitalized schizophrenic patients (37 men and 21 women; average age 35) who had been ill for an average of 11.4 years; the second comprised 31 normal, first-degree relatives of the schizophrenic patients (18 men and 13 women; average age 39); and the third group consisted of normal control subjects (16 women and 22 men; average age 36). Only one relative of each schizophrenic patient could participate in the study. While the schizophrenic group had significantly higher numbers of NSS than the control group, their scores did not differ significantly from the scores of the first-degree relatives. The relative group demonstrated higher NSS scores than the control group, but lower (although not significantly so) NSS scores than the schizophrenic group. In the schizophrenic group, neither length of illness, or current neuroleptic (anti-psychotic) drug dosage was found to be related to NSS. The finding of abnormal NSS in first-degree relatives of schizophrenic patients indicates that NSS may prove to be useful biological markers for schizophrenia in populations at risk. (Consumer Summary produced by Reliance Medical Information, Inc.)

Schizophrenia

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Olfaction and psychiatry

Article Abstract:

Studies have found that impairments in odor detection, identification, and intensity levels are related to increasing age and the degeneration of tissue that lines the nasal passages. Odor impairment has also been linked with the onset of Alzheimer's disease (AD). One study found that AD patients had more olfactory deficits (i.e. pertaining to smell) than patients with multi-infarct dementia. Neurological studies have shown that the anterior olfactory nucleus of AD patients tends to contain senile plaques, tangles of small fibers inside nerve cells, and a reduced number of cells. Odor deficits have also been linked with Parkinson's disease (PD), although it is not known if the olfactory deficits in AD and PD share a common cause. Alcoholic patients diagnosed with Korsakoff's psychosis (KP) have been shown to have more severely impaired olfaction than non-KP alcoholics or normal subjects. Olfactory deficits have also been reported in schizophrenia, Huntington's chorea, Down's syndrome, and depressive disorder. Although the data provide only preliminary indications of relationships between olfactory deficits and specific pathology, there seem to be three important reasons for continuing research: (1) specific sensory deficits may help to localize specific pathology; (2) detailed olfactory testing may allow for earlier diagnosis and treatment; and (3) olfactory pathways may prove to be the means of transmission of certain neuropsychiatric diseases. Biopsy of nasal sensory mucosa may play a future diagnostic role in the assessment of neuropsychiatric disorders. (Consumer Summary produced by Reliance Medical Information, Inc.)

Health aspects, Smell, Parkinsonism

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