Neurological soft signs discriminate schizophrenia from major depression but not bipolar disorder

Neurological soft signs (NSS) are minor neurological abnormalities, including motor, sensory, and inhibitory dysfunction. Schizophrenia and other neuropsychiatric disorders are associated with a higher prevalence of NSS. However, the relationships between NSS and schizophrenia, bipolar disorder, and major depression are unclear. The present study aimed to examine the specificity of NSS among these three clinical groups.

A total of 120 demographically matched participants (30 each in schizophrenia, bipolar disorder, major depression, and healthy controls) were recruited for the study. NSS subscales of the Cambridge Neurological Inventory (CNI) were administered to each participant.

Significant differences were found in the total score of NSS (p<0.01), and the subscale scores for motor coordination (p<0.01), sensory integration (p=0.01) and disinhibition (p<0.01). Both patients with schizophrenia and bipolar disorder showed more total NSS signs than healthy controls (p<0.01). Patients with schizophrenia also showed more total NSS signs than patients with major depression (p=0.02). Both patients with schizophrenia and patients with bipolar disorder showed more motor coordination signs than healthy controls and patients with major depression (p<0.05). Moreover, compared with healthy controls, patients with schizophrenia showed more disinhibition signs (p<0.01), while patients with bipolar disorder showed more sensory integration signs (p<0.01). Discriminant analysis showed 77.5% of correct classification of patients with schizophrenia and bipolar disorder from patients with major depression and healthy controls.

NSS are not unique to schizophrenia, but are also found in bipolar disorder, while patients with major depression are comparable to normal controls. Our results suggest that NSS, especially motor-coordination signs, can differentiate schizophrenia from major depression but not bipolar disorder. Our results may provide further evidence to support the similarity between schizophrenia and bipolar disorder from the dimension of behavioral expression.