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Olfaction in neurodegenerative disorder
1Essex Centre for Neuroscience, Oldchurch Hospital, Romford, Essex, United Kingdom. chrishawkes@msn.com
Summary
Olfactory dysfunction, or impaired sense of smell, is common in Parkinson's disease (PD) and Alzheimer's disease (AD). This smell deficit may even precede motor or cognitive symptoms, offering potential early diagnostic clues.
Area of Science:
- Neurology
- Neuroscience
- Ophthalmology
Background:
- Olfactory dysfunction, including anosmia (loss of smell), is increasingly recognized as a significant feature in neurodegenerative diseases.
- The potential for smell impairment to serve as an early diagnostic marker for conditions like Parkinson's disease (PD) and Alzheimer's disease (AD) has garnered significant interest.
Purpose of the Study:
- To review the prevalence and clinical significance of olfactory dysfunction in various neurological disorders.
- To assess the diagnostic utility of smell testing in Parkinson's disease (PD), Alzheimer's disease (AD), parkinsonian syndromes, essential tremor, motor neurone disease (MND), and Huntington's chorea (HC).
Main Methods:
- Literature review of studies examining olfactory function in PD, AD, and related neurological conditions.
- Analysis of diagnostic criteria and clinical observations related to smell impairment in these diseases.
Main Results:
- Olfactory dysfunction is frequent and often severe in PD and AD, potentially preceding motor and cognitive symptoms.
- Normal smell identification in PD is rare and may indicate a misdiagnosis, except in female patients with tremor-dominant disease.
- Anosmia is atypical in progressive supranuclear palsy and corticobasal degeneration, warranting diagnostic review.
- Smell impairment is observed in individuals at risk for parkinsonism and is associated with an increased risk of AD in ApoE-4 carriers.
- Smell testing has limited clinical value in Huntington's chorea and motor neurone disease.
- Olfactory nasal neuron biopsy shows non-specific changes and does not aid current diagnosis in PD and AD.
Conclusions:
- Olfactory dysfunction is a common and early feature of Parkinson's disease and Alzheimer's disease, with potential diagnostic implications.
- Smell testing can be a valuable, non-invasive tool for early detection and differential diagnosis in specific neurodegenerative conditions.
- Further research into the mechanisms and specific biomarkers of olfactory dysfunction in neurodegeneration is warranted.