Advances in Understanding Parosmia: An fMRI Study

Introduction: A number of patients with a diminished sense of smell also can suffer from parosmia. These patients with such a qualitative smell disorder are often more severely affected than patients exhibiting only a quantitative smell disorder. Qualitative smell disorders have heretofore been poorly investigated. The focus of the present study was, using functional MRI, to compare the central processing of olfactory stimulation in patients with qualitative smell disorders.

Material and methods: A total of 23 patients were investigated, 12 hyposmic patients without parosmia (HYP group) and 11 hyposmic patients with parosmia (PAR group). Both groups were matched with regard to sex and age. The olfactory smells used were peach and coffee odors.

Results: The two groups exhibited different patterns of activation. In HYP patients a stronger activation was observed in the medial orbitofrontal cortex, anterior cingulate cortex, and parahippocampal gyrus, whereas in the PAR group stronger activation in the thalamus and putamen was seen.

Discussion: These results are consistent with the hypothesis that there are specific patterns in the central processing of olfactory stimuli which differ in hyposmic patients with and without parosmia.