Similarity and disparity of obsessive-compulsive disorder and schizophrenia in MR volumetric abnormalities of the hippocampus-amygdala complex

Abstract

Objectives: Given that obsessive-compulsive disorder (OCD) and schizophrenia may share clinical symptoms as well as functional brain abnormalities, this study was designed to clarify common and different morphological abnormalities in OCD and schizophrenia. Methods: Volumes of the hippocampus, the amygdala, and the thalamus were measured in three age and sex matched groups of 22 patients with OCD, 22 patients with schizophrenia, and 22 normal subjects using three dimensional magnetic resonance imaging. Volume tracing was performed manually on serial coronal slices with the references of sagittal or axial planes using internal landmarks. Results: Hippocampal volume was bilaterally reduced in both OCD and schizophrenic patients versus the normal controls. Left amygdala volume was significantly enlarged in patients with OCD but not in patients with schizophrenia versus the normal controls. The thalamus did not show any volumetric group differences. Conclusions: Non-specific hippocampal reduction in both the OCD and schizophrenic groups is likely to link to a clinical overlap between the two illnesses, whereas the left amygdala enlargement observed only in the OCD patients seems to be suggestive of a unique role for the amygdala in the pathophysiology of OCD.A lthough OCD and schizophrenia are separate psychiatric disorders, patients having comorbidities of the two illnesses are frequently found in clinical practice. Based on functional and structural neuroimaging findings, the possible overlap has been also identified in the pathophysiology of the two illnesses, in particular abnormalities in the frontostriatal circuits.1 Other candidate structures for such overlapping pathophysiology may include the thalamus and/or the hippocampus-amygdala complex. It is noteworthy that although similar regions have been identified to be functionally or morphologically abnormal in both illnesses, they tend to occur in opposite directions: for example, hyperfunctional fronto-striatal systems in OCD, 2 but hypofunctional in schizophrenia 3 ; and thalamic enlargement in OCD, 4 but thalamic reduction in schizophrenia. 5Based on such significant but different findings of similar regions in OCD and schizophrenia, we hypothesised that the two illnesses would also show quite different abnormal patterns in the hippocampus-amygdala complex. Moreover, it was expected that such morphological changes, if identified, would correspond to hyperfunctional circuitry in OCD, but hypofunctional circuitry in schizophrenia. To test this hypothesis, volumes of the hippocampus, the amygdala, and the thalamus were compared in patients with OCD, in patients with schizophrenia, and in normal subjects. METHODS SubjectsThere were three age and sex matched groups: OCD, schizophrenia, and normal subjects. Each group consisted of 22 subjects (15 men and 7 women), who were all right handed, and had a mean age of 26.7 (SD 7.2), 26.6 (SD 6.5), and 26.2 (SD 6.1) years, respectively. Patients were recruited from Seoul National University Hospital, and none had a dual...

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