Olfaction and neurodegeneration in HD.

Olfactory deficits are present in many neurodegenerative diseases. It is not known, however, whether the olfactory deterioration is caused by a common neural deficit, or whether it is unique to each disease. We report here the effect of degeneration of different brain structures on olfactory impairment in Huntington's disease as determined by voxel-based morphometric analysis. The structures with the greatest effect on the olfactory deficit were the entorhinal cortex, the thalamus, the parahippocampal gyrus, and the caudate nucleus. Although various neuroimaging studies have shown previously that the caudate nucleus is involved in olfaction, this is the first demonstration that it is related to an olfactory dysfunction in a neurodegenerative disease. The results are discussed in relation to other neurodegenerative diseases.