Orthonasal, but not Retronasal Olfaction Is Specifically Impaired in Parkinson's Disease.

Olfactory dysfunction (OD) in Parkinson's disease (PD) appears several years before the presence of motor disturbance. Olfactory testing has the potential to serve as a tool for early detection of PD, but OD is not specific to PD as it affects up to 20% of the general population. Olfaction includes an orthonasal and a retronasal components; in some forms of OD, retronasal olfactory function is preserved. We aimed to evaluate whether combined testing components allows for discriminating between PD-related OD and non-Parkinsonian OD (NPOD). The objective of this study is to orthonasal and retronasal olfactory function in PD patients and compare them to a NPOD group and to healthy controls. We hypothesized that this combined testing allows to distinguish PD patients from both other groups. We included 32 PD patients, 25 NPOD patients, and 15 healthy controls. Both olfactory components were impaired in PD and NPOD patients, compared with controls; however, NPOD patients had significantly better orthonasal scores than PD patients. Furthermore, the ratio of retronasal/orthonasal score was higher in PD than in both other groups. In the NPOD group, orthonasal and retronasal scores were significantly correlated; no such correlation could be observed in PD patients. In summary, PD patients seem to rely on compensatory mechanisms for flavor perception. Combined orthonasal and retronasal olfactory testing may contribute to differentiate PD patients from patients with NPOD.

Chemosensory perception is specifically impaired in Parkinson's disease.

Patients with Parkinson's Disease (PD) exhibit a considerably diminished sense of smell. The olfactory system is intimately connected to the trigeminal system, responsible for the perception of sensations such as freshness, warmth or piquancy in odorants. Usually, olfactory impairment is associated with a similar reduction of trigeminal sensitivity. A recent study suggests that the trigeminal system is not affected in patients with PD. To test this, we evaluated perception of mixed olfactory/trigeminal stimuli in 23 patients with idiopathic PD and compared them to 22 healthy matched controls. More specifically, we evaluated the trigeminal dimensions of coolness, warmth and piquancy and the olfactory dimensions of pleasantness, familiarity and edibility of 10 mixed olfactory/trigeminal odorants using Likert scale. We show that PD patients perceive trigeminal sensations of coolness, warmth, and piquancy of odorants equally well as controls, as opposed to olfactory dimensions that are perceived significantly less compared to controls (p < 0.001). Moreover, Chi-square Tests show that equal number of participants in both groups perceive the trigeminal dimensions of odorants. Thus, we provide further evidence that the trigeminal system, as opposed to the olfactory system, is not impaired in PD patients reflecting a specific pattern of chemosensory impairment in PD.

Trigeminal system in Parkinson's disease: A potential avenue to detect Parkinson-specific olfactory dysfunction.

BACKGROUND: Olfactory dysfunction (OD) is very frequent in Parkinson's disease (PD) and observed years before diagnosis. The trigeminal system, a chemosensory system allowing for the perception of spiciness, freshness, etc., is intimately connected to the olfactory system and although usually reduced in OD the trigeminal system is not well characterized in PD. We hypothesize that measuring trigeminal sensitivity potentially allows to discriminate between OD due to PD and OD due to other causes to potentially help the development of an early diagnostic tool. OBJECTIVE: To evaluate olfactory and trigeminal sensitivity and perception in PD patients and compare them to participants with non-parkinsonian OD (NPOD) and to healthy controls. METHODS: We assessed olfactory function using "Sniffin' Sticks test" and trigeminal function with the localization task in 28 PD patients, 27 healthy controls and 21 patients with OD unrelated to PD. RESULTS: PD patients exhibited significantly higher trigeminal sensitivity than NPOD patients (p = 0.002) and performed similar to healthy controls. In contrast, PD and NPOD patients had both similar olfactory scores, significantly below healthy controls. CONCLUSION: The trigeminal system seems not to be impaired in PD patients even in the presence of OD. Measuring trigeminal sensitivity may therefore allow to differentiate PD-related OD from other forms of OD.

Autopsy as gold standard in FDG-PET studies in dementia.

Positron emission tomography (PET) imaging with F18-fluorodeoxyglucose (FDG) is increasingly used as an adjunct to clinical evaluation in the diagnosis of dementia. Considering that most FDG-PET studies in dementia use clinical diagnosis as gold standard and that clinical diagnosis is approximately 80% sensitive or accurate, we aim to review the evidence-based data on the diagnostic accuracy of brain FDG-PET in dementia when cerebral autopsy is used as gold standard. We searched the PubMed and Medline databases for dementia-related articles that correlate histopathological diagnosis at autopsy with FDG-PET imaging and found 47 articles among which there were only 5 studies of 20 patients or more. We were able to conclude that sensitivity and specificity of FDG-PET for Alzheimer's disease are good, but more studies using histopathological diagnosis at autopsy as gold standard are needed in order to evaluate what FDG-PET truly adds to premortem diagnostic accuracy in dementia.