Olfactory impairment in first-episode schizophrenia: a case-control study, and sex dimorphism in the relationship between olfactory impairment and psychotic symptoms

Background: A body of studies has focused on the olfactory impairment among people with schizophrenia. The effect of sex on this relationship has attracted the attention of researchers. These issues have not been studied much in Chinese schizophrenia patients. Methods: We conducted a case-control study of 110 first-episode antipsychotic medicine naive schizophrenia patients aged 18-35 years and 110 controls, matched by age and sex. Odour threshold, discrimination and identification were assessed by the Sniffin' Sticks test. Psychotic symptoms were assessed by the Positive and Negative Syndrome Scale (PANSS). Results: The odour threshold, discrimination and identification scores of patients with schizophrenia were significantly lower than those of the healthy control group. The difference in identification score had statistical significance between male and female patients with schizophrenia (t = -2.45, P < 0.05). Controlling for confounding factor, in male schizophrenia participants, the negative subscale score was significantly and inversely correlated with the discrimination (gamma = -0.37, p < 0.008), identification (gamma = -0.45, p < 0.008) and TDI (gamma = -0.50, p < 0.008) scores; the general psychopathology subscale score was inversely and significantly correlated with the identification (gamma = -0.47, p < 0.008) and TDI (gamma = -0.41, p < 0.008) scores. For female schizophrenia patients, positive and general psychopathology subscale scores had a significant inverse correlation with the identification score (positive: gamma = -0. 47, p < 0.008; general psychopathology: gamma = -0.42, p < 0.008). Conclusions: Controlling for confounder, negative symptoms were related to impaired odour discrimination and identification in male schizophrenia patients, while positive symptoms were correlated with impaired odour identification in female schizophrenia patients. This sex dimorphism could provide useful information for future studies aiming to finding biomarkers of schizophrenia.