Curr Opin Neurol 2004 Aug;17(4):417-23
The National Hospital for Neurology and Neurosurgery, Queen Square, London, UK.
PURPOSE OF REVIEW: Marked olfactory dysfunction (hyposmia) is a frequent and early abnormality in Parkinson’s disease. We review recent advances related to its cause and its clinical relevance with respect to the differential diagnosis of Parkinsonian syndromes.
RECENT FINDINGS: Marked olfactory dysfunction occurs in Parkinson’s disease and dementia with Lewy bodies but is not found in progressive supranuclear palsy and corticobasal degeneration. In multiple system atrophy, the deficit is mild and indistinguishablefrom cerebellar syndromes of other aetiologies, including the spino-cerebellar ataxias. This is in keeping with evidence of cerebellar involvement in olfactory processing, which may also help to explain recent findings of mild olfactory dysfunction in essential tremor. Smell testing remains, however, a clinically relevant tool in the differential diagnosis of indeterminate tremors. Intact olfaction has also been reported recently in Parkinson’sdisease (PARK 2) and vascular Parkinsonism. The relevance of sniffingability tool faction and a possible role of increased tyrosine hydroxylase and dopamine parts of the olfactory bulb are issues of current interest with respect to the physiology. The early or ‘pre clinical’ detection of Parkinson’s disease is increasingly recognized as an area in which olfactory testing may be of value.
SUMMARY: Research findings have confirmed a rolefor olfactory testing in the differential diagnosis of movement disorders, and suggest that this approach is currently under used in clinical practice. Validated test batteries are now available that may prove to be of practical use in the differential diagnosis of Parkinsonian syndromes and indeterminate tremors.