Objective: The authors investigated whether primary negative symptoms of schizophrenia are enduring or treatment-responsive.
Methods: Previously, a double-blind, random-assignment trial of the novel antipsychotic olanzapine (in low, medium, and high dose ranges), placebo, or haloperidol (10-20 mg/day) for 335 schizophrenic inpatients was conducted for up to 52 weeks. Changes in the treatment groups from baseline to endpoint in summary scores on the Scale for the Assessment of Negative Symptoms (SANS) and several secondary measures were compared. This article describes a path analysis to determine to what extent the total treatment effect on negative symptoms was direct or indirect (i.e., mediated by differential effects on positive symptoms, extrapyramidal symptoms, or mood).
Results: Significantly greater improvement was achieved with high-dose olanzapine than with placebo or haloperidol. Olanzapine had a significantly greater direct effect than placebo on all SANS dimensions except anhedonia-asociality. Olanzapine also demonstrated a significantly greater direct effect than haloperidol on negative symptoms, especially on the dimensions of affective flattening and avolition-apathy. Olanzapine's superior effects were replicated in a subgroup with SANS-defined prominent negative symptoms (N = 116) and a subgroup with a BPRS-defined cross-sectional proxy for the deficit state (N = 117).
Conclusions: These results suggest that the negative symptoms of schizophrenia are directly responsive to treatment. The significantly greater direct and indirect effects of olanzapine than of haloperidol on negative symptoms are likely related to olanzapine's pleotrophic pharmacology, which includes dopaminergic, serotonergic, muscarinic, and adrenergic activities. The results contribute to the hypothesis that negative symptoms may be under the influence of several neurotransmitters within one or more neuroanatomic circuits.