Olfactory Deficits in Schizophrenia: Nuances, Complexities, Clinical Correlates, and Potential Susceptibility Biomarker

Background Multiple studies have reported olfactory deficits (OD) in schizophrenia (SCZ). However, the OD in SCZ may differ from the loss of smell known to occur in patients with other neurodegenerative disorders. We reviewed the clinical and neurobiological correlates of OD in SCZ reported in controlled published studies. Methods Using search engines, including PubMed, Medline databases, and Google Scholar, we used keywords including schizophrenia, psychosis, olfaction, and olfactory deficits, and collated the clinical and biological correlates previously reported in controlled studies of OD. Results 17 publications were identified over the past 30 years. We identified the following correlates: (1) OD is associated with severity of negative symptoms and verbal memory impairment, (2) OD are present in medication naïve patient groups, (3) odor identification tends to be worse in male SCZ patients, (4) OD tends to be worse in the left nostril, and (5) deficits persist despite improvement in psychotic symptoms with antipsychotic therapy. Discussion OD in SCZ appears to be a trait present before the onset of psychosis, not related to treatment, present in a subtype, mostly males, and is more impaired in the left nostril than the right. Further studies are warranted to exploit OD as a biomarker.