Unirhinal olfactory identification deficits in young male patients with schizophrenia and related disorders: association with impaired memory function.

We have observed discreet subgroups of male patients with psychotic disorders who have unirhinal olfactory identification deficits (microsmia). The purpose of this study was to examine the relationship between left or right nostril microsmia and performance on literalised neuropsychological tests sensitive to lesions in brain areas implicated in the pathogenesis of schizophrenia. Sixty-six male patients diagnosed with schizophrenia or related disorders were assessed with a battery of neuropsychological tests, sensitive to literalised and regional (temporal and frontal lobe) dysfunction. The University of Pennsylvania Smell Identification Test (UPSIT) was administered unirhinally and resultant scores were used to classify patients into olfactory subgroups. Neuropsychological test scores were compared amongst subgroups. A mixed design MANOVA was performed on cognitive domains with olfactory status (right microsmic; RM, n=8, left microsmic; LM, n=20, and normosmic schizophrenic controls; NSzC, n=38) as the between subject factor while hemisphere (left versus right) and domain (executive/fluency versus memory) were within-subject factors. A three-way (olfactory subgroup by hemisphere by region) interaction was observed. Non-verbal memory impairment was observed in the right and left microsmic subgroups. Verbal memory deficits were demonstrated in patients with left nostril microsmia. These results indicate that unirhinal olfactory performance may provide a meaningful manner by which to subtype patients with schizophrenia. Moreover, the data suggest that olfactory deficits in patients with schizophrenia are associated with dysfunction of temporal lobe, rather than frontal lobe abnormalities. The data are consistent with reports linking the right temporal lobe integrity to adequate olfactory processing.