Certain subtypes of major depression, particularly if associated with severe psychomotor retardation or psychotic features, may be difficult to differentiate from schizophrenia due to overlapping symptoms. The aim of this study was to assess the potential role of polysomnography as a tool for differentiating between severe depression with or without psychotic features and schizophrenia. Forty patients aged 18 to 50 years were recruited, comprising 20 with severe depression and 20 with schizophrenia who had defaulted from follow-up visits and had been off their medications for over a week. Two successive overnight polysomnographic recordings were done for all patients. Rapid eye movement latency was 26 ± 6.9 minutes and 43.9 ± 16.9 min in patients with depression and schizophrenia, respectively, with a statistically significant difference between the groups (P < 0.006). Rapid eye movementintensity was 34 ± 14% in depressed patients and 21.4 ± 4.5% in patients with schizophrenia, again with a statistically significant difference between the groups (P<0.015). On the other hand, stage IV intensity was significantly (P < 0.03) lower in patients with schizophrenia (9 ± 7.9%) than in depressed patients (17.8 ± 9.2%). Polysomnographic parameters are different in schizophrenia and severe depression. Further research to assess cutoff scores for different polysomnographic parameters are needed to enable the utilization of polysomnography as a potential electrophysiologic tool for differentiating between these diagnoses.
Key words: Depression, schizophrenia, polysomnography, sleep, encephalography.
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