Schizotypal personality disorder and MRI abnormalities of temporal lobe gray matter

Abstract

Background: Structural MRI data indicate schizophrenics have reduced left-sided temporal lobe gray matter volumes, especially in the superior temporal gyrus (STG) and medial temporal lobe. Our data further suggest a specificity to schizophrenia spectrum disorders of STG volume reduction. Interpretation of research studies involving schizophrenics may be complicated by the effects of exposure to neuroleptics and chronic illness. Sharing the same genetic diathesis of schizophrenics, subjects with schizotypal personality disorder (SPD) offer a unique opportunity to evaluate commonalities between schizophrenia and SPD, particularly as SPD subjects are characterized by cognitive and perceptual distortions, an inability to tolerate close friendships, and odd behavior, but they are not psychotic and so have generally not been prescribed neuroleptics nor hospitalized. Evaluation of brain structure in SPD may thus offer insight into the "endophenotype" common to both disorders. In addition, differences between groups may suggest which are the brain structures of schizophrenics that contribute to the development of psychosis.

Methods: To test the hypothesis of whether SPD subjects might show similar STG abnormalities, STG and medial temporal lobe regions of interest (ROI) were manually drawn on high resolution coronal MRI 1.5 mm thick slices. Images were derived from 16 right-handed male SPD subjects, without regard to family history, and 14 healthy, right-handed, comparison males who did not differ from the SPD group on parental socio-economic status, age, or verbal IQ.

Results: As predicted, SPD subjects showed a reduction in left STG gray matter volume compared with age and gender matched comparison subjects. SPD subjects also showed reduced parahippocampal left/right asymmetry and a high degree of disordered thinking. Comparisons with chronic schizophrenics previously studied by us showed the SPD group had a similarity of left STG gray matter volume reduction, but fewer medial temporal lobe abnormalities.

Conclusions: These abnormalities strengthen the hypothesis of a temporal lobe abnormality in SPD, and the similarity of STG findings in schizophrenia and SPD suggest that STG abnormalities may be part of the spectrum "endophenotype." It is also possible that presence of medial temporal lobe abnormalities may help to differentiate who will develop schizophrenia and who will develop the less severe schizophrenia spectrum disorder, SPD.

Figure 1

(A) SPGR coronal image demonstrating the manual delineation of the ROI in a SPD subject. Image right side is the left side of the brain. The left STG is shown in red, the right in magenta, left hippocampus is in orange, the right in green, the left parahippocampal gyrus is in bright blue, and the right in purple. (B) MRI 3D rendering of a SPD subject’s brain with the left STG highlighted in red. For clearer visualization of the gyral structure, the brain surface was eroded one voxel in constructing this figure.

Figure 2

Left STG absolute gray matter volumes of each subject. Only 2/14 of healthy comparison subjects have left STG volumes less than the SPD mean. Horizontal lines and values indicate group means.

Figure 3

Z score graph (SD = 1) comparing the ICC adjusted STG gray matter volume for subjects in the schizophrenic (Shenton et al 1992) (n = 15), SPD (n = 16), and combined comparison (control) group from both the schizophrenic and SPD studies (n = 29).

Figure 4

Graph displaying the degree of formal thought disorder using the Thought Disorder Index for schizophrenic (Shenton et al 1992), SPD, and sub-threshold subjects.