xRead - Olfactory Disorders (September 2023)

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494

INTERNATIONAL CONSENSUS ON OLFACTION

TABLE VIII.3 (Continued) Study

Year LOE Study design

Study groups 268 patients with

Clinical end point

Conclusions

UPSIT R Morphology of

MRI is able to identify damage in

Doty

1997 4

Prospective case series

et al 312

PTOD (MRI was performed in 15)

olfactory-related brain structures

olfactory-related brain structures

Yousem

1996 4

Prospective case series

25 patients with PTOD

UPSIT R Morphology of

88% posttraumatic

et al 1073

patients had abnormal MRI findings Lesions mainly involved OB, olfactory tract, and inferior frontal lobes More severe OD was associated with greater OB and olfactory tract volume loss Patients with congenital anosmia had aplastic or hypoplastic OB and OT

olfactory-related brain structures

Yousem

UPSIT R Morphology of

1996 4

Prospective case series

25 patients with congenital anosmia

et al 1074

olfactory-related brain structures

BAST-24 = Barcelona Smell Test-24; CCCRC = Connecticut Chemosensory Clinical Research Center; CT = computed tomography; ERP = event-related potential; ID = identification; IOD = idiopathic olfactory dysfunction; LOE = level of evidence; MRI = magnetic resonance imaging; OB = olfactory bulb; OB = olfactory bulb volume; OC = olfactory cleft; OD = olfactory dysfunction; OS = olfactory sulcus; PIOD = postinfectious olfactory dysfunction; POC = primary olfactory cortex; PTOD = posttraumatic olfactory dysfunction; QOD = Questionnaire of Olfactory Disorders; SNOT-22 = 22-item Sino-Nasal Outcome Test; SPECT = single-photon emission computerized tomography; SS-ID = Sniffin’ Sticks identification only; SS-TDI = Sniffin’ Sticks threshold, discrimination, identification combination; T&T = Toyoda and Takagi; TDI = threshold, discrimination, and identification; UPSIT R = University of Pennsylvania Smell Identification Test; VAS = visual analog scale. *Adjustment was made toward reduction of quality since randomization was made regarding olfactory training while imaging results were analyzed at the level of the whole group (similar to a case series study).

olfactory sulcus. 917,934,1059,1060,1069,1074 In postinfectious olfactory loss, OBV is decreased, and the OB may exhibit signal changes with central hyper-T2 signal. 1054 Patients with PTOD exhibit typical lesions, mainly at the level of the OB, olfactory tract, temporal, and/or frontal lobes. 309,310, 312,1058,1062,1073 MRI has been found to have a high accuracy in detecting PTOD. 1070 The earliest study about MRI in PTOD reported that 88% of patients had abnormal MRI findings. 1073 Therefore, MRI is of paramount importance for the medicolegal assessment of PTOD. MRI is also interesting to evaluate the global brain mor phology and olfactory pathways. Besides showing typical lesions in patients with posttraumatic olfactory loss, it has been described that OF was associated with overall MRI brain changes 1066 (one case series) but also that parosmia and phantosmia could be related to lesions in specific brain areas 309 (one retrospective study). In addition, brain MRI is also considered to reveal potential intracranial causes underlying IOD, and, notably, to exclude brain tumors. A retrospective study 1024 evaluated the cost-effectiveness of MRI in patients with IOD and found that abnormalities were identified in 4.6% of patients, with only 0.8% of patients having OD attributable to an imaging finding. The investigators estimated that the cost per attributable

abnormal finding was $325,000 USD. Therefore, the routine use of MRI in patients with IOD is debatable. It is widely acknowledged that olfactory loss may con stitute an early sign of neurodegenerative diseases, such as PD or AD. Therefore, patients with idiopathic smell loss are at times considered at risk for developing ND. However, no study has investigated the usefulness of structural MRI for the early diagnosis of these diseases in patients with idiopathic smell loss. MRI for evaluation and diagnosis of OD Aggregate grade of evidence : C (Level 3: 12 studies; Level 4: 20 studies). Benefit : Identification/confirmation of the etiology, exclusion of intracranial tumor, objective correlate of OF and prognosis, medicolegal value. Harm :Minimal. Cost :High. Benefit-harm assessment : Relative balance of benefit andharm. Value judgments : While MRI has been found to be very useful in some cases, only low-level evidence supports its use, and it is costly. Policy level :Option.