xRead - Olfactory Disorders (September 2023)

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401

PATEL et al.

TABLE VII.11 (Continued) Study

Year LOE Study design Study groups

Clinical end point

Conclusions

Murphy et al 114

2002 2

Cross-sectional

EHLS adult participants

Subjective and objective (SDOIT)

Overall OD prevalence 24.5%, in patients > 80 years 62.5%, accuracy of self-report worsens withage increases with odds ratios of 1.78 for every 5-year increment of age Link between caregiver dependence and OD independent of age Incidence of OD

Schubert et al 521

2011

2

Longitudinal population based

EHLS adult participants

Objective (SDOIT)

Sulmont Rossé et al 526

2015 2

Cross-sectional

Aupalesens project participants

Objective (ETOC, proprietary

discrimination tests)

BAST-24 = Barcelona Smell Test-24; B-SIT = Brief Smell Identification Test; ETOC = European Test of Olfactory Capabilities; EHLS = Epidemiology of Hearing Loss Study; ERP = event-related potential; LOE = level of evidence; MRI = magnetic resonance imaging; NHANES = National Health and Nutrition Examination Survey; NHIS = National Health Interview Survey; NSHAP = National Social Life, Health, and Aging Project; OB = olfactory bulb; OD = olfactory dysfunction; ODT = odor detection threshold; OFFE = Olfactory Function Field Exam; OLFACT-RL = Osmic Enterprises Olfactometer; OSN = olfactory sensory neuron; PST = Pocket Smell Test; SDOIT = San Diego Odor Identification Test; SOIT = Scandinavian Odor Identification Test; SS = Sniffin’ Sticks; SS-ID = Sniffin’ Sticks identification only; SS-TDI = Sniffin’ Sticks threshold, discrimination, identification combination; UPSIT R = University of Pennsylvania Smell Identification Test.

Interestingly, a recent meta-analysis also attempted to compare the OF deficits between patients with AD and those with PD to determine which olfactory measures may be most useful in screening for these distinct patient populations. They found that all olfactory measures were affected in patients with AD and PD in comparison with healthy controls, but that identification (and in AD, recog nition) were more strongly affected than detection. After multiple post hoc tests were performed, olfactory detection appeared to be more strongly affected in patients with PD compared with patients with AD. 793 Although AD and PD are two of the most common and widely known types of dementia, there are several others. OD is seen in frontotemporal dementia, with difficulty in detection and recognition but preserved identification in the behavioral variant and dysfunction seen in the seman tic variant but with not enough data to further parse any difference in testing modalities. 850 Lewy body dementia and rapid eye movement sleep behavior disorder, now sus pected as a potential prodrome to Lewy body dementia and PD, have also both been associated with olfactory deficits, but only in smaller and lower LOE studies thus far. 800,808 As more subtypes of dementia emerge, it is likely that OF may predict these as well, as the olfactory system appears to be the “canary in the coal mine” of neurocognitive ability. Cognitive testing in older patients with olfactory deficits. Aggregate grade of evidence : A (Level 1: four studies; Level 2: seven studies; Level 3: 57 studies; Level 4: 265 stud ies).

evaluating OF in individuals with subjective cognitive decline and in healthy older adults found that there was a significant difference, with slight relative impairment in patients with subjective cognitive decline. 668 In the Mayo Clinic Study of Aging, participants were classified as having normal cognition, amnestic MCI, nonamnestic MCI, or dementia. This population-based prospective cohort study found that olfactory impairment is associated with amnestic MCI and the progression of amnestic MCI to AD dementia. 638 A quantitative meta-analysis was performed on 31 pre vious studies including the one above comparing OF in patients with MCI and healthy older adults. This also found that olfactory deficits are present and robust in patients with MCI compared with healthy older adults, and that the most prominent alteration appears to be in olfac tory identification scores. 646 The association between smell loss and PD has long been known, but the ability to predict the development of PD using OF as a predictor has only been studied more recently. A systematic review and meta-analysis was published in 2019 evaluating the use of hyposmia as a predictive factor for PD. Of 1783 studies retrieved in the authors’ search, only seven met requirements for inclusion. Inclusion requirements were a prospective human study, baseline olfactory test before any diagnosis of PD, reported relative risks, odds ratios, and hazard ratios with 95% confidence intervals or report data with which those could be calculated. Based on the data from these studies, the authors found that hyposmia leads to a 3.84-fold increase in risk of developing PD compared with normosmia. 841