Contributions of Olfactory and Neuropsychological Assessment to the Diagnosis of First-Episode Schizophrenia

Objective: First-episode schizophrenia and schizoaffective patients (SZ+) show olfactory impairments, but how these relate to cognitive dysfunction remains unclear. We examined the relationship between cognitive and olfactory dysfunction in SZ+ and the clinical utility of these measures in the assessment of SZ+ patients. Method: First-episode SZ+ patients (n = 63) and controls (n = 63) were administered tests of odor identification and discrimination in addition to measures of manual dexterity, processing speed, attention and working memory, executive functioning, ideational fluency, and memory. We analyzed the relationships between olfactory and cognitive variables and conducted stepwise multiple regressions to identify which cognitive indices best predicted olfactory performance within the SZ+ group. Linear discriminant analysis was used to identify which measures best distinguished cases from controls. Results: Among patients, odor discrimination correlated with perseverative errors and odor identification correlated with bilateral manual dexterity. Odor discrimination performance was best predicted by perseverative errors and letter fluency, whereas odor identification ability was best predicted by manual dexterity. Stepwise linear discriminant analysis revealed that manual dexterity, letter-guided word fluency, and odor discrimination best distinguished SZ+ from healthy adults. Conclusions: These findings indicate that manual dexterity, letter-guided word fluency, and odor discrimination may provide incremental information that strengthens a diagnosis of SZ+. Although odor discrimination tasks have received limited attention in schizophrenia studies, the extant data along with the present results indicate that odor discrimination tasks may have utility over odor identification measures as a neurodevelopmental risk marker. Additional studies examining odor discrimination as a predictor of SZ spectrum illness are warranted. Our findings suggest that smell deficits are present in first-episode schizophrenia patients, show unique relationships with specific measures of cognitive ability, and may help discriminate first-episode schizophrenia patients from healthy controls. Additional studies on the use of odor discrimination as a biomarker in the early identification of schizophrenia patients are needed.