Impaired Olfactory Identification of Patients with Cerebrovascular Disease Can Be Revealed by Dual Testing

The importance of an olfactory assessment of individuals with neurological diseases has attracted attention. Cerebrovascular disease is one of the most common diseases in Japan, but there are few reports on olfaction in patients with stroke. Herein we examined olfaction in patients with stroke.

We assessed 50 patients hospitalized for neurorehabilitation after stroke. For the assessment of olfaction, the dual tests known as the T&T olfactometry (T&T) test and the odor identification Open Essence (OE) test were administered. Since the OE test was introduced only recently in Japan, 100 healthy volunteers participated to provide OE data as the control group. We analyzed the patients’ T&T and OE data and the controls’ OE data, and we investigated the relationship between the olfaction data and the patients’ stroke-induced lesion areas.

None of the patients reported experiencing inconvenience due to olfactory loss, although we classified 45 (90%) patients as hyposmic or anosmic based on their identification thresholds on the T&T test as well as their significantly low OE scores compared to the control data. However, the patients’ perception thresholds on the T&T test were in the normal range. Brain computed tomography examination data revealed that odor identification was not impaired in about half of the 23 patients with a putamen-thalamus lesion. In addition, our correlation analysis of each odorant in the OE test indicated that six of the 12 odorants are sufficient for olfactory assessments.

The results of the dual olfactory tests revealed that patients with stroke showed impaired odor identification but intact odor perception. It is possible that the direct pathway from the piriform cortex to the orbitofrontal cortex is essential for odor identification.

Because of their normal odor perception, most patients with stroke are not aware of their impaired odor identification. A set of six of the 12 odorants used in the OE test is capable of representing the total OE score, and its use will save time for olfactory tests in clinical assessments.