Olfactory dysfunction in schizophrenia: a qualitative and quantitative review.
Olfactory dysfunction in patients with schizophrenia has been a topic of increasing interest, with deficits in odor identification, detection threshold sensitivity, discrimination, and memory being reported. Despite increasing knowledge, controversy has existed about possible differential deficits among olfactory tests as well as the influences of gender, smoking, and medication status on olfactory measures. To help elucidate some of this controversy, we conducted a qualitative and quantitative (meta-analytic) review of the English language literature on olfaction in schizophrenia. Moderator variables such as gender, medication status, and smoking history were also examined. Results indicated that substantial olfactory deficits, across all domains, are observed in patients with schizophrenia. No differential deficits were observed across domains of odor identification, detection threshold sensitivity, discrimination, and memory. The influences of gender, medication status, and smoking on effect sizes were not significant across studies. This supports the hypothesis of primary dysfunction in the olfactory system that is regulated by brain regions where structural and functional abnormalities have also been reported in neuroimaging studies.