xRead - Olfactory Disorders (September 2023)

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INTERNATIONAL CONSENSUS ON OLFACTION

TABLE VIII.13 Diagnostic use of the EOG

Clinical end point Presence of EOG response

Study

Year 1989

LOE Study design

Study groups

Conclusions

Patients with “peripheral” cause of olfactory loss have fewer responses than those with “central” loss The number of EOG responses increases with increasing OF

Furukawa et al 1283

4

Observational

Patients with olfactory loss (n = 34)

Turetsky et al 1284

2009

3

Observational

Patients with

EOG amplitude Larger EOG amplitudes in

schizophreia (n = 21)

schizophrenic patients compared with controls

HCs (n = 18)) Patients with

Patients with olfactory loss have less EOG responses than HCs Normosmic patients have more EOG responses than hyperosmic or anosmic participants

Presence of EOG response

Hummel et al 1285

2018

3

Observational

idiopathic and postinfectious olfactory loss (n = 38)

Following OT in patients the number of EOG responses increased

HCs (n = 27)

EOG = electro-olfactogram; HC = healthy control; LOE = level of evidence; OF = olfactory function; OT = olfactory training.

technique has been used extensively in animal research since the 1930s, 1268,1269 its use in human olfaction research has been limited. Although pioneering work was performed in the 1960s 1270 to 1980s, 1271 EOG research never arrived in rou tine clinical assessment probably because of the require ments for sophisticated constant-flow olfactometry, 1271 nasal endoscopy, 1272 and the relatively low response yield of ≈ 50% to 70% with high interindividual variability and low intraindividual variability. 1273–1276 Among other results, EOGs have been used to pro vide evidence for the dominant role of the CNS in olfac tory desensitization. Specifically, repeated stimulation at short interstimulus intervals produce responses with lit tle or no decrease in amplitude, although simultane ously recorded, electroencephalography-derived olfactory ERPs exhibit such a decrease in amplitudes and inten sity ratings decrease. 1271,1277 Leopold et al 1278 used EOGs to functionally describe the extent of the OE. 1278 They reported the presence of EOG responses and function ally mature OSNs at the insertion level of the middle turbinate. Some EOG work also suggested the existence of a specific topographical distribution of ORs with some recording sites only responding to certain odors, 1272 and that the EOG was odorant specific 1273 (and even specific for odorous enantiomers 1279 ). Areas that responded max imally to a pleasant odorant were also likely to respond strongly to other pleasant odorants, and a location that responded maximally to an unpleasant odorant was likely to respond strongly to other unpleasant odorants. 1274 EOG recordings have also been used to show that peripheral

antagonism between odors results in a decrease of odor intensity. Specifically, the odorant bourgeonal (scent of lilies of the valley) is a potent agonist at the human OR hOR17-4. Its antagonist undecanal decreases EOG response amplitudes and intensity of bourgeonal follow ing brief exposure to undecanal. 1280 In addition, EOG recordings suggested that individuals who perceived large differences among odorants also had large EOG differ ences among odorants. 1274 More recent work utilized EOG responses to display that psychological conditioning pro duced significant differences in the peripheral responses between the conditioned and the unconditioned stimulus, demonstrating contextually induced changes at the level of the first neuron in the olfactory system. 1281 Similarly, using EOG recordings it was possibly to show that the decreased intensity from retronasally presented odors compared with orthonasal presentation may start at the periphery. 1282 When focusing on the clinical utility of EOG recordings, a literature search produced 17 results. After careful read ing of abstracts, only three relevant publications were eli gible to be included in the formal analysis (Table VIII.13). On a clinical level, EOG recordings were significantly more often obtained in healthy participants than in patients with OD, suggesting that olfactory disorders are accompanied by a change at the level of the olfactory mucosa. 1283,1285 In addition, OT was associated with a sig nificant increase in the number of EOG recordings in response to odors, suggesting improvement in OF with training. 1285 Overall, EOG measurements provide an oppor tunity to record objective neuronal input from the