Neurologic soft signs (NSS) can differentiate schizophrenia from major depression but not bipolar disorder, study findings indicate.
Raymond Chan, from the Chinese Academy of Sciences in Beijing, and colleagues found that NSS, particularly motor-coordination signs, were increased in patients with schizophrenia, but also in those with bipolar disorder, whereas patients with major depression were comparable to mentally healthy individuals.
The findings suggest that "patients with schizophrenia and bipolar disorder appear to be biologically more similar to each other than patients with major depression," say the researchers.
They add that the results are consistent with the concepts of "schizophrenia-bipolar disorder boundary" and "unitary psychosis" in that schizophrenia and bipolar disorder patients share a number of similarities, including brain structure abnormalities and NSS.
Symptoms and related neurocognitive functions can then be distributed on a continuum with unipolar depression and schizophrenia at opposite ends and bipolar disorder lying between the two, but closer to the schizophrenia end.
As reported in Progress in Neuro-Psychopharmacology & Biological Psychiatry, the researchers assessed NSS in 30 patients with schizophrenia, 30 with bipolar disorder, and 30 with major depression using the Cambridge Neurological Inventory.
Total scores were significantly higher, indicating more NSS, in patients with schizophrenia and bipolar disorder, at an average 5.03 and 4.77, respectively, compared with 3.07 in patients with major depression and 2.33 in mentally healthy individuals.
No significant difference was found between healthy controls and patients with major depression in total NSS or any of the NSS subscores, and there was no significant difference between patients with bipolar disorder and schizophrenia.
Subscale scores also showed that patients with schizophrenia and bipolar disorder had more motor-coordination signs than mentally healthy controls and patients with major depression. Patients with schizophrenia also had more disinhibition signs than mentally healthy controls, while patients with bipolar disorder showed more sensory integration signs than mentally healthy controls.
Preliminary discriminant analysis indicated that according to NSS scores patients with schizophrenia or bipolar disorder could be correctly classified from patients with major depression and mentally healthy individuals 77.5% of the time.
"The specificity of NSS expression has the potential to help the discrimination of schizophrenia and bipolar disorder from disorders less likely to have a neurodevelopmental component such as major depression," the researchers conclude.
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