Novas técnicas de neuroimagem em psiquiatria: qual o potencial de aplicações na prática clínica?

At its simplest, voxel-based morphometry (VBM) involves a voxel-wise comparison of the local concentration of gray matter between two groups of subjects. The procedure is relatively straightforward and involves spatially normalizing high-resolution images from all the subjects in the study into the same stereotactic space. This is followed by segmenting the gray matter from the spatially normalized images and smoothing the gray-matter segments. Voxel-wise parametric statistical tests which compare the smoothed gray-matter images from the two groups are performed. Corrections for multiple comparisons are made using the theory of Gaussian random fields. This paper describes the steps involved in VBM, with particular emphasis on segmenting gray matter from MR images with nonuniformity artifact. We provide evaluations of the assumptions that underpin the method, including the accuracy of the segmentation and the assumptions made about the statistical distribution of the data. Copyright 2000 Academic Press.

Late-life depression is associated with increased subcortical white matter hyperintensities. There is some evidence that they are associated with a poorer response to acute treatment. Neurological signs and neuropsychological dysfunction are further evidence of abnormalities in the brain, but they have not been studied in relation to therapy resistance. A prospective study of 24 normal controls and 75 consecutive elderly (aged 65 to 85) patients with DSM-III-R major depression entered a naturalistic study of treatment. Assessment of response to monotherapy and then lithium augmentation or ECT created three outcome groups. Investigations included magnetic resonance brain imaging, neuropsychological and neurological examination. Response to monotherapy within 12 weeks was shown by 42.7%, a further 37.3% responded to lithium augmentation or ECT within 24 weeks and 20% had responded poorly to all treatments at 24 weeks. Subcortical hyperintensities were significantly increased in the more resistant patients. These included confluent deep white matter, multiple (> 5) basal ganglia lesions and pontine reticular formation lesions. Most of the neuropsychological impairment was restricted to the resistant groups and was of a subcortico-frontal type. Extrapyramidal, frontal and pyramidal neurological signs characterized the resistant groups. The combination of extrapyramidal signs, pyramidal tract signs and impairment of motor hand sequencing strongly predicted resistance to 12 weeks of antidepressant monotherapy with 89% sensitivity and 95% specificity. In late-life depression a poor response to antidepressant monotherapy can be expected in those patients with a frontal lobe syndrome, extrapyramidal signs or if MRI T2-weighted lesions are present in both the basal ganglia and the pontine reticular formation.

Single photon emission computed tomography (SPECT) of regional cerebral blood flow (RCBF) has been employed experimentally in the assessment of patients with dementia. The standard with which the SPECT diagnosis has been compared previously has been the initial clinical diagnosis. Recognizing that histopathologic diagnosis would be a more reliable standard, the authors compared SPECT diagnoses and clinical diagnoses with histopathologic diagnoses in a series of 18 patients who had been referred by the Alzheimer Disease Research Center. SPECT RCBF studies were carried out prospectively in 15 patients with an inhaled xenon-133 SPECT technique and in three patients with technetium-99m hexamethyl-propylene-amine oxime and triple-camera-scanner SPECT. When compared with histopathologic diagnosis, clinical diagnosis was correct in 15 of 18 patients; visual scanning diagnosis, in 13 of 18; and Xe-133-SPECT diagnosis based on quantitative ratios in regions of interest, in 14 of 15 (13 of 13 with Alzheimer disease).