Specificity and sensitivity of the Self-assessment of Negative Symptoms (SNS) in patients with schizophrenia

OBJECTIVES

Negative symptoms can be present at any stage of schizophrenia but their evaluation remains challenging. Self-evaluations may be particularly useful in screening negative symptoms quickly and effectively. The purpose of this study was to determine the sensitivity, the specificity, and the threshold beyond which the negative symptoms are considered pathological in a comparative study between patients with schizophrenia and healthy subjects using the Self-assessment of Negative Symptoms (SNS).

METHODS

One hundred and nine patients with schizophrenia and schizoaffective disorders (DSM-5) and 99 healthy controls were included and evaluated with the SNS. AUROC analyses were performed to assess the discriminant performance of the SNS scale for screening negative symptoms in the whole sample of patients but also in 2 patient sub-samples without high scores of depression or negative symptoms.

RESULTS

The SNS (AUROC = 0.942 ± 0.046; p < 0.001) appears to be an appropriate screening tool for distinguishing between SZ and HC with a threshold value of 7, and the sensitivity and specificity were 92.7% (95CI = [86.1-96.8]) and 85.9% (95CI = [77.4-92.1]) respectively. A threshold at 7 was also observed in the samples without patients with high level of depressive or negative symptoms.

CONCLUSION

These results indicate that SNS might be a valuable tool for screening negative symptoms in clinical practice regardless the level of depressive and negative symptoms. Further studies using SNS in subjects at high risk for psychosis or with a first psychotic episode would be useful in the detection of negative symptoms.

[Validation of the French version of the self-evaluation of negative symptoms (SNS)]

INTRODUCTION

Schizophrenia is a disorder affecting 1% of the population and is associated with severe functional impairment. Negative symptoms are responsible for the majority of this impairment, and many patients with schizophrenia have negative symptoms. However, their evaluation is still a challenge. Thus, standardized assessments are needed to facilitate identification of these symptoms. Many tools have been developed, but most are based on observer ratings. Self-evaluation can provide an additional outcome measure and allow patients to be more engaged in their treatment. The Self-evaluation of Negative Symptoms (SNS) has been developed recently. This is a remarkably understandable instrument for patients with schizophrenia as it allows them to readily complete it without assistance, providing information with respect to their own perception of negative symptoms. The SNS is a self-assessment that permits patients to evaluate themselves in 5 dimensions of negative symptoms. This validation study for the SNS revealed good psychometric properties alongside satisfactory acceptance by patients.

AIM

This study was to confirm the validation of the French version of the self-evaluation of negative symptoms (SNS).

METHODS

Patients with schizophrenia or schizoaffective disorder according to the DSM-IV-R, with a stable regimen of anti-psychotic drugs for the last two months, aged more than 18 years old were eligible for the study. Symptoms were rated using the SNS, the Scale for the Assessment of Negative Symptoms (SANS), the Calgary Depression Scale for Schizophrenics (CDSS), the Brief Psychiatric Rating Scale (BPRS) and the Clinical Global Impression and Parkinsonism. Patients were asked to fulfill the SNS twice, 6 weeks apart.

RESULTS

Sixty patients were evaluated. Cronbach's coefficient (α=0.8) showed good internal consistency. The SNS significantly correlated with the SANS (r=0.6), the negative sub-score of the BPRS (r=0.6) and the Clinician Global Impression on the severity of negative symptoms (r=0.7). SNS scores did not correlate with level of insight (r=0.08) or Brief Psychiatric Rating Scale positive sub-scores (r=0.2). SNS scores correlated with CDSS scores. However, we did not find correlation between the first item of the CDSS which evaluates depression and the "diminished emotional range" sub-score of SNS. The test-retest of SNS revealed no changes of scores at two evaluations 6 weeks apart.

CONCLUSION

The acceptance by patients of the SNS was excellent. The French version of the SNS demonstrated a good internal consistency, good convergent validity and good discriminant validity. The study demonstrates the ability of patients with schizophrenia to accurately report their own experiences. Self-assessments of negative symptoms should be more widely employed in clinical practice because they may allow patients with schizophrenia to develop appropriate coping strategies.