xRead - Olfactory Disorders (September 2023)

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INTERNATIONAL CONSENSUS ON OLFACTION

TABLE VIII.4 (Continued) Study

Year LOE Study design

Study groups

Clinical end point

Conclusions

Voxel-based

Anosmic patients had significant decrease of gray matter volume in several olfactory-related brain regions Longer disease duration was associated with increased atrophy Recruitment of neural networks was correlated toOF Neural networks utilized were the same between patients with OD and controls, but functional connectivity differed Functional connectivity changed after 12 weeks of OT

Bitter

2010 3

Prospective cohort

14 anosmic patients 17 normosmic controls

et al 1087

morphometry

Reichert

2018 4

Case series

48 patients with OD (29 anosmia, 19 hyposmia) 10 patients with OD 14HCs 7 with OD followed upafterOT

SS-TDI fMRI: brain activation

et al 1077

to olfactory stimulation

SS-TDI fMRI: brain activation

Kollndorfer et al 1079

2015 4

Case series

to olfactory stimulation

CA = congenital anosmia; fMRI = functional magnetic resonance imaging; HC = healthy control; IOD = idiopathic olfactory dysfunction; LOE = level of evidence; MRI = magnetic resonance imaging; OBV = olfactory bulb volume; OD = olfactory dysfunction; OF = olfactory function; OFC = orbitofrontal cortex; OS = olfactory sulcus; OT = olfactory training; PD = Parkinson disease; PIOD = postinfectious olfactory dysfunction; POC = primary olfactory cortex; SS-TDI = Sniffin’ Sticks threshold, discrimination, identification combination; T&T = Toyoda and Takagi.

Value judgments : These techniques require particular setup, specific analytic techniques, and expertise. More over, fMRI studies show a high interindividual variabil ity. Although these advanced techniques are useful for the understanding of olfactory processing, they are currently not adapted for use in the clinical setting. Policy level : No recommendation for clinical purposes at this time. Intervention : Currently, these techniques are not adapted to the clinical environment, and their value at an individual level is questionable. Research is needed to decrease the interindividual variability and establish true clinical benefit before considering them for clinical use. 4 Nuclear medicine techniques We have found six studies using nuclear medicine tech niques to examine olfaction (Table VIII.5: four prospective cohort studies, two retrospective case series). One prospective cohort study evaluated brain metabolism using fluorodeoxyglucose-positron emis sion tomography under olfactory stimulation. 1091 It showed that brain metabolism in certain brain regions is significantly different between patients with IOD and controls, 1092 with a correlation between disease duration and fluorodeoxyglucose uptake.

Two studies (one prospective cohort study and one retrospective case series) have investigated, using single photon emission computerized tomography, the migra tion of nasally administrated thallium. It was found that thallium migration to the OB was lower in patients with OD and correlated with olfactory threshold and OBV. 1093 Also, high thallium migration was associated with a bet ter prognosis of olfactory recovery. 1067 Three other single photon emission computerized tomography–based studies (two prospective cohort studies and one retrospective case series) found that, after olfactory stimulation, the mean brain, frontal, temporal, and parietal perfusions were sig nificantly lower in patients with PTOD. 1062,1094 Moreover, regional brain perfusion was able to diagnose PTOD with a high accuracy, 1070 which was even better than MRI. Use of nuclear medicine imaging to evaluate OD. Aggregate grade of evidence : C (Level 3: four studies; Level 4: two studies). Benefit : Single-photon emission computerized tomog raphy could be beneficial for the diagnosis of PTOD (eg, medicolegal use). Nasal-thallium migration could be indicative of the prognosis of recovery. Harm : Minimal to moderate (use of radioisotopes). Cost :High. Benefit-harm assessment : Balance of benefit and harm.