Resumen

MONTOYA, Alonso; LEPAGE, Martin  y  MALLA, Ashok. Disfunción estructural del lóbulo temporal en pacientes con un primer episodio psicótico de esquizofrenia. Salud Ment [online]. 2005, vol.28, n.2, pp.33-39. ISSN 0185-3325.

Magnetic resonance imaging (MRI) has been useful in revealing subtle structural differences in the brains of schizophrenic patients compared with healthy controls. MR structural analyses have revealed a number of brain abnormalities including ventricular enlargement, total brain volume reduction, and regional reductions in brain volume in frontal, parietal and temporal regions.

However, it is still unknown whether the brain abnormalities observed with MRI in schizophrenia are confounded by chronicity or whether there is a continual degenerative process. Evaluation of the brain structure during the first episode of psychosis (FEP) is a powerful strategy for investigating these fundamental questions. The first-episode design avoids the confusion of chronicity of illness, longstanding substance abuse, and the effects of treatment.

Structural MRI studies of patients experiencing a first-episode psychosis have revealed a similar pattern of brain abnormalities as in samples of chronic patients, although deficits may be less extensive. The temporal lobe, a brain structure traditionally implicated in the pathophyisiology of schizophrenia, has been examined often in first-episode studies. Many studies have reported significant abnormalitites in the medial areas and superior temporal gyri. However, most studies examining the whole temporal lobe have been unable to show such significant abnormalities.

In the light of the increasing amount of ambiguous findings regarding structural temporal lobe abnormalities in patients with schizophrenia experiencing their first-episode of psychosis, a quantitative review of the existing literature was needed to better characterize the temporal lobe deficits observed with MRI in those patients.

Thus we conducted a systematic review of structural MRI studies of patients with first-episode schizophrenia in which volume measurements of temporal lobe structures were reported. Using meta-analytical methods, we carried out an analysis of the temporal lobe volumes in these FEP patients and the comparison subjects. In addition to solving the problems of traditional narrative reviews, a meta-analysis provides tools for integrating quantitative data from multiple studies, improving the overall effect size of variables of interest, and increasing statistical power.

Eighteen studies were identified as suitable for the present analysis. These studies included 575 FEP patients and 738 control subjects. The average number of patients across studies was 32. The majority of patients in the studies were male (62%) and the average age of patients was 27 years old. In terms of structural brain findings, and assuming a volume of 100% in the comparison group, we found that the mean temporal volume of subjects with FEP was smaller (95%), as well as the analysis of regional structures such as left amygdala (95%), hippocampus-amygdala (left 92%, right 94%), hippocampus (left 85%, right 96%), and left temporal lobe (97%). Right temporal lobe volume was slightly greater (104%) and there was no difference in the volume of the right amygdala.

Although this review was focused on evaluating the findings on temporal lobe deficits in patients with a first episode of psychosis, other brain region volumes were analyzed. The whole brain volume (95%) and frontal lobe volume (right 98%, left 99%) were lower in patients than in the comparison subjects.

It is important to consider several potential limitations of this study. The first one has to do with the methodology employed to analyze structural MRI data. The method of choice in investigating the distribution of subtle cerebral pathology in schizophrenia has been an examination of anatomically defined regions of interest (ROI) within the brain. This method has some limitations, including the manual tracing of ROI on successive brain slices, a time consuming process that does not easily allow for the comparison of many brain regions or for the examination of volume differences in large samples of subjects. Furthermore, the question of validity is relevant as the ROI is investigator-determined and depends on the complex interindividual variability of the brain.

The other method used in two studies included in this review is the voxel-based morphometry (VBM). This is an automated statistical method for examining structural MR images of the brain. VBM methodology makes voxel-wise comparisons of the local concentrations of grey matter between two groups of subjects and offers a more rapid and extensive survey of grey matter abnormalities in patients than ROI analysis. An important limitation of this methodology is that it has less regional sensitivity compared to the ROI technique and that these differences have to be considered in the interpretation of the results.

Secondly, although our review only considered studies with patients experiencing a first episode of psychosis in schizophrenia (and not affective psychotic disorders), the fact that different investigators used somewhat different criteria when making their diagnoses could have introduced a potential bias in our inclusion process. Thus, it is possible that our results can not be generalized to the full population of first-episode patients. For instance, although most of the studies included used either DSM-IV diagnostic criteria (16 studies) or the Research Diagnostic Criteria (2 studies), variability may arise because many authors did not consider previous psychotic episodes in which patients were treated with antipsychotic medications for less than 30 days.

In conclusion, this meta-analysis suggests that schizophrenic patients present temporal lobe differences, mainly diminished volume values in mesial temporal lobe structures during the initial presentation of a first episode of their illness. However, our results indicated that there was also evidence of global volume changes and regional volume decreases in the frontal lobes of these patients. This data, derived from patients in the early courses of their illness, is compatible with developmental hypotheses of schizophrenic abnormalities and with the view of schizophrenia as a neuropsychiatric disorder with marked deficits in the temporal lobes.

However, the central questions in schizophrenia research regarding which brain abnormalities are independent of psychosis and which evolve before and after psychosis begins still remain unanswered. We think that these questions can be addressed by longitudinal neuroimaging studies beginning in the prodromal phase of the illness or by evaluating high-risk subjects during the critical period of transition to first-episode psychosis.

Palabras llave : Schizophrenia; first-episode of psychosis; magnetic resonance imaging; brain imaging; temporal lobe.

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