This work was a prospective study conducted on 60 amMCI patients attending the outpatient clinics of The Neuropsychiatry Department, Tanta University Hospitals in the period from 4 April 2016 to 15 December 2017.
The included patients’ ages were 55–65 years (to avoid age-related changes in the studied parameters). Amnestic MCI was diagnosed according to the DSM-V criteria of mild neurocognitive disorder in which the person’s concerned persistent memory decline ≥ 6 months with Montreal Cognitive Assessment (MoCA) scale of 23–25 points which is a valid scale used in MCI assessment (Nasreddine and Patel 2016; Abdel Rahman and El Gaafary 2009).
The included 60 amMCI patients underwent baseline full neurological examination, MoCA, PSG, MRI–HPC and ERC volumetry, and auditory MMN at the beginning of the study. Fifty-six of the included patients continued the study, which they continued follow-up for 1 year; at the end of which, the MoCA scale was repeated and divided the included subjects to 17 progressive amMCI patients (group I) and 39 amMCI subjects passed a stationary or regressive course (group II) (37 stationary and 2 regressive). The study also included 20 age- and body mass index (BMI)-matched healthy control subjects (HCS) (group III). Amnestic MCI was considered progressive if the follow-up MoCA score is lowered ≥ 3 points (≥ 1.5 standard deviation of normal), stationary if the score changed 1–2 points, and regressive if the score increases ≥ 3 points (Horton et al. 2015).
Exclusion criteria included illiterate subjects (to unify the MoCA scale and keep homogeneity of the studied sample), people with MRI contraindications, patients with history of cerebrovascular disorders, major depressive disorder, chronic metabolic or endocrinal disorders, chronic sleep disorders, drug abusers, and chronic use of medications affecting cognition. Patients with hearing problems or middle ear dysfunctions were also excluded after doing a full audiological history, otological examination, and basic audiological evaluation including pure tone audiometry for the frequency range 250–8000 Hz and speech audiometry (using GSI-61 audiometer) and immittancemetry (using Zodiac Madsen).
The protocol of this study was approved by The Research Ethics Committee and Quality Assurance Unit, Faculty of Medicine, Tanta University. Participations were voluntary, informed consents were obtained from all participants prior to their commencements in the study, and detailed information concerning the aims of the study and the possible risks were clarified.
Polysomnography was done by Somon Medics Gmbh machine (Type: SOMNO screenTMplus, SN: 4259, kw45: 2014, Am SonnenstuhL63, D-97236 Rander Sacker, Germany), modified V2 lead ECG, electrooculography (LOC-A1/A2 and ROC-A1/A2), EEG channel montages (O1/A2, C3/A2, C4/A1, and O2/A1), and surface tibial and submental EMG. Thermal airflow sensors were used for nasal and oral signals, and microphone was applied for tracheal sounds assessment. Chest and abdominal efforts were measured by dual thoracoabdominal RIP (respiratory inductance plethysmography) belts. PSG was scored according to The American Academy of Sleep Medicine Manual for the Scoring of Sleep and Associated Events: Rules, Terminology and Technical Specifications, (version 2.4), 2017 (Berry et al. 2017)
Three-dimensional HPC/ERC–MRI volumetric assessment were performed according to Bonilha and colleague (2012) and by the practice of The Harvard University Slicer version software (http://www.slicer.org/) Functool, GE Healthcare, Milwaukee, WI, USA. The images were attained by a 1.5-Tesla, General Electric Scanner (GE Medical Systems, Milwaukee, USA) with quadrature eight-channel head coil.
Auditory MMN was done using Smart Evoke Potential, Home Intelligence Service (HIS), USA and used the oddball paradigm with tone stimuli at 1000 and 2000 Hz as standard and deviant stimuli, respectively, 150 ms durations, 1/s repetition rate, 15% deviant probability and at 70 dB nHL (decibel above normal adult hearing level). MMN was defined as the most prominent negativity following N100 and was calculated according to manual specification of SmartEP, HIS.
Statistical analysis was conducted using SPSS version 19, 2011, created by IBM, Chicago, IL, USA. For numerical values, the range and mean ± SD were calculated. The differences between subcategories were tested using the z-score, ANOVA, and post-ANOVA tests. p value < 0.05 was considered statistically significant.