Table 3.
Characteristics of studies included in the POC systematic review.
| Authors | Participants’ Selection | Group Comparability | POC Measurement | Sample Size | Mean Age (SD) | Outcome |
|---|---|---|---|---|---|---|
| Al-Otaibi et al., 2020 [77] |
+ Diagnostic according to the National Institute on Aging—Alzheimer’s Association (NIA-AA) criteria. + MMSE to qualify controls as cognitively normal. + Participants underwent a pre-screening visit including medical history questionnaire and blood analysis. − No random recruitment. − Poor description of control’s recruitment. − No description of controls’ health history. −No measurement of AD-pathology biomarker (PET/CSF tau and amyloid-β). |
+ Control for sex, age, and education. | + Siemens 1.5 T MR scanner. + T1-weighted sequence. + Automatic segmentation using the Automatic Anatomical Labelling atlas. Targeted structures: the olfactory tract, amygdala, piriform cortex, anterior perforated substance, the subcallosal area (including the subcallosal cingulate gyrus), and the anterior cingulate cortex. − Olfactory tract is included in the definition of the olfactory cortex although it is constituted of white matter. + Same method for both groups. |
AD: 14 Controls: 25 |
AD: 75.06 (4.60) Controls: 71.1 (5.22) |
Olfactory cortex volume is significantly smaller in patients with AD compared to healthy older controls. The decrease was more apparent in the left olfactory cortex. |
| Lu et al., 2019 * [78,79] |
+ Use of the Clinical Dementia Rating, the MMSE, the CVLT-II, the Dementia Rating Scale and a reviewed of the medical records of AD and MCI patients. + Controls were from the same community and without cognitive deficits. − No random recruitment. − Poor description of control’s recruitment. − No description of controls’ health history. − No distinction between amnesic and non-amnesic MCI. −No measurement of AD-pathology biomarker (PET/CSF tau and amyloid-β). |
+ Control for age. | + Siemens Trio 3.0 T scanner. + T1-weighted MPRAGE sequence. − Manual segmentation. Targeted structures: the anterior olfactory nucleus, olfactory tubercle, piriform cortex, anterior portion of the periamygdaloid cortex, amygdala, and anterior perforated substance. + Same method for both groups. |
AD: 26 EMCI: 36 LMCI: 31 Controls: 44 |
AD: 71.55 (7.3) EMCI: 71.69 (7.3) LMCI: 72.41 (7.4) Controls: 74.18 (6.1) |
There was a decreasing trend for a smaller POC volume dependent on AD disease state, but no difference reach significance (Controls > LMCI > EMCI > AD). |
| Vasavada et al., 2015 [53] |
+ Diagnostics were made by a certified neurologist using NINCDS-ADRDA criteria (AD) and Peterson criteria (MCI). − Poor description of recruitment procedures. − No distinction between amnesic and non-amnesic MCI. − No measurement of AD-pathology biomarker (PET/CSF tau and amyloid-β). |
+ Correction for intracranial volume and age. | + Siemens 3.0 T MRI system. + T1-weighted MPRAGE images. − Manual segmentation. Targeted structures: the anterior olfactory nucleus, olfactory tubercle, piriform cortex, anterior portion of the periamygdaloid cortex and amygdala, and anterior perforated substance. + Same method for both groups. |
AD: 15 MCI: 21 Controls: 27 |
AD; 71.9 (11.9) MCI: 73.2 (9) Controls: 69.5 (10.4) |
MCI and AD patients had a significantly lower POC volume than controls. The difference between AD and MCI patients did not reach significance. |
Note: AD: Alzheimer’s disease, LMCI: Late mild cognitive impairment, EMCI: Early mild cognitive impairment, NINCDS-ADRDA: National Institute of Neurological and Communicative Disorders and Stroke and the Alzheimer’s Disease and Related Disorders Association, MMSE: Mini-Mental State Examination, CVLT-II: The California Verbal Learning Test Two. * The data set was provided by the authors and has been used in both studies [78,79].