Abstract
Background
Dementia, mainly caused by Alzheimer's disease (AD), is a leading cause of mortality and disability in the elderly. However, inconsistencies in diagnostic and inclusion criteria challenge the design and comparability of AD clinical trials.
Objective
To review recent AD clinical trials, focusing on diagnostic methods and inclusion criteria, and identify trends and gaps to inform future research.
Methods
We systematically searched Web of Science, PubMed, and Google Scholar for AD clinical trials, extracting data on diagnostic criteria, disease stage, cognitive assessments, biomarker use, and participant age.
Results
Of the 27,471 articles screened, 71 studies were included in the final review. Most were conducted in North America (52%) and Europe (34%). NINCDS–ADRDA (56%) and NIA–AA 2011 (30%) were the most used diagnostic criterion, with the latter increasingly adopted in recent years. Over half focused on mild-to-moderate AD (56%), 16% on mild AD, and 13% included mild cognitive impairment/mild AD populations, with growing interest in early-stage interventions. However, only a minority reported notable cognitive improvements. The Mini-Mental State Examination was the most frequently used assessment tool (86%), though 36 different cutoff schemes were identified. Biomarkers were used in 38% of studies, mainly in the past three years, while others relied on symptom-based or imaging approaches. Participants ranged from 45 to 95 years old, with 50 as the most common lower age limit.
Conclusions
Symptom-based criteria still dominate AD trials. Given the limited efficacy of single interventions, future studies should consider multimodal, non-invasive approaches and prioritize objective biomarkers to enhance consistency and diagnostic precision.
Keywords
Introduction
With global aging, the number of people with dementia is forecasted to reach 153 million by 2050, while annual worldwide costs already surpassed $1.3 trillion. 1 Alzheimer's disease (AD), the most common type of dementia, accounts for 60–80% of cases. 2 Despite billions in research funding, drug interventions have largely failed to yield significant cognitive improvement. 3 While recently approved disease-modifying therapies (DMT), such as lecanemab and donanemab,4,5 can slow disease progression, they do not provide a cure, underscoring the need for improved treatment strategies and early, accurate diagnosis. 6
Over the past century, AD diagnostic criteria have evolved significantly. Early classifications required postmortem confirmation, but the National Institute of Neurological and Communicative Disorders and Stroke and the Alzheimer's Disease and Related Disorders Association (NINCDS–ADRDA, 1984) criteria introduced premortem clinical diagnosis, 7 later refined by the International Working Group (IWG, 2007, 2014, 2021)8–10 and the National Institute on Aging–Alzheimer's Association (NIA–AA, 2011, 2018).11,12 These revisions reflect an evolving understanding of AD progression and the underlying amyloid and tau pathology. Most recently, in 2024, the Alzheimer's Association Workgroup (AA) incorporated plasma biomarker phosphorylated tau (p-tau) 217 into the diagnostic criteria, marking a shift toward blood-based biomarkers for non-invasive early detection. 13 In contrast, clinical diagnostic systems such as ICD-10, DSM-IV, DSM-IV-TR, and DSM-5 continue to emphasize symptom-based dementia diagnosis after ruling out other causes.14–16 However, significant heterogeneity remains in how diagnostic and inclusion criteria are applied in clinical research. Most existing guidelines are either biomarker-centered8,9,12,13 or diease-centred,7,15 often reflecting regional expertise 17 or the perspectives of small expert groups. 18 This variability in patient selection and diagnostic thresholds undermines study reliability, making consistent conclusions in AD trials challenging. 17
Despite the critical role of standardized diagnostic frameworks in ensuring rigorous research, 19 few studies have systematically analyzed the inclusion criteria used across AD-related randomized controlled trials (RCTs). To address this gap, our study reviews AD-related RCTs from the past decade, identifying key commonalities and discrepancies in diagnostic and inclusion criteria. By mapping these variations, our findings will provide valuable insights into current research practices and serve as a reference for clinicians and researchers, working toward greater diagnostic precision and treatment efficacy in AD.
Methods
Search strategy
This systematic review adhered to the guidelines of the 2009 Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA). 20 The PROSPERO-registered ID is CRD42023470858.
PubMed, Web of Science, and Google Scholar databases were used to identify studies for inclusion in this review, focusing on articles published between 01/01/2014 and 12/01/2024. The search used the terms: “Alzheimer's disease” or “AD” AND “Randomized Controlled Trial” or “RCT” or “Clinical Trials.” Previously published systematic reviews were also examined to identify additional relevant articles.
Inclusion criteria
Study inclusion criteria were: (1) AD cohort; (2) clinical RCT research article type; (3) well-defined and explicit diagnostic and inclusion criteria; (4) clinical registration number included; and (5) written in English.
Data extraction
The study selection process followed a three-step procedure (Figure 1). Duplicate articles were excluded. The titles and abstracts of the remaining articles were independently screened by two reviewers (Y.L. and S.L.) based on predefined inclusion criteria. Articles not meeting the inclusion criteria, such as those involving non-AD cohorts, other pathologies, other article types, or other clinical entities, were excluded. Finally, a third reviewer (S.C.) evaluated the quality and accuracy of the selected data. Any disagreements between reviewers were resolved through discussion until a consensus was reached.

Flow diagram of the literature search and study selection process. Number of studies/articles (n) per step are indicated. * One eligible study was added post-review due to omission in search.
Results
Search results and study characteristics
A total of 27,471 articles were identified from 3 databases (PubMed, 2871; Web of Science, 4259; Google Scholar, 20,341). After excluding 3480 duplicates, 23,765 articles were removed for reasons such as non-AD focus, animal studies, and studies on healthy individuals. This left 226 articles, from which 59 were excluded for lacking a Clinical Trial Identifier, 51 for not applying clear diagnostic criteria, and 46 for not detailing inclusion criteria. During the peer review process, one additional eligible article missed in the initial search due to search strategy limitations, which was identified based on reviewer suggestion and met all inclusion criteria. 21 It was therefore included in the final synthesis. In total, 71 studies were included in this systematic review. The selection process is detailed in Figure 1.
In addition, the authors of the included studies are mainly concentrated in the North America (52%), followed by Europe (34%), Asia (10%), and Oceania (4%). The United States is the leading country in AD research, followed by the United Kingdom, Sweden, Spain, and the Netherlands (Figure 2). We have also compiled the diagnostic and inclusion criteria from the studies analyzed, and the results are presented in Table 1.

Distribution of the first authors’ affiliated countries in the included studies. The United States conducts the highest number of AD clinical studies.
Detailed inclusion criteria for all the included studies.
ADAS-Cog: Alzheimer's Disease Assessment Scale–Cognitive Subscale; BPRS: Brief Psychiatric Rating Scale; CDRS: Clinical Dementia Rating Score; CDR-SB: Clinical Dementia Rating–Sum of Boxes; CDR-GS: CDR−Global Score; CES-D: Center for Epidemiologic Studies Depression Scale; CESDS: Center for Epidemiological Studies Depression; CSDD: Cornell Scale for Depression in Dementia; CSF, cerebrospinal fluid; CSS: Cornell scale score; CT, computed tomography; FAST: Functional Assessment Staging of Alzheimer's disease; GDS: Geriatric Depression Scale; GMS: Geriatric Mental Schedule; HAMD: Hamilton Depression Scale; HIS: Hachinski Ischemic Scale; MCI, mild cognitive impairment; MoCA: Montreal Cognitive Assessment; MMSE: Mini-Mental State Examination; MRI, magnetic resonance imaging; NPI: Neuropsychiatric Inventory; PET, positron emission tomography; FCSRT: Free and Cued Selective Reminding Test; WMS-R: Wechsler Memory Scale-revised; TMT: Trail Making Test; RBANS: Repeatable Battery for the Assessment of Neuropsychological Status; RBANS-DMI: Repeated battery of tests for the assessment of neuropsychological status-delayed memory DSRS: dementia severity rating scale; RCSRT: Free and cued selective reminder tests; RMHIS: Rosen-modified Hachinski ischemic score; WMVPAT: Wechsler Memory Visual Paired Association Test.; ISLT: International Shopping List Test Immediate Recall; ISLR: International Shopping List Test Delayed Recall; /: Indicates non-relevance.
Diagnostic criteria
Overview. We found the most commonly used diagnostic criteria were the earliest NINCDS-ADRDA criteria (n = 40, 56%), followed by the NIA-AA 2011 (n = 20, 30%). The DSM-IV were used in 7% of studies (n = 5), while the IWG-1 and IWG-2 were each used in 6% (n = 4). The DSM-IV-TR criteria accounted for 4% (n = 3), and DSM-5 was used in 3% (n = 2). The NIA-AA 2018 and NIA-AA 2012 each represented 1% (n = 1). Moreover, 16% of those studies (n = 11) employed a combination of two or more diagnostic criteria. The use of NIA-AA 2011 has become increasingly popular in recent years. The results are shown in Figure 3.

Utilization of diagnostic criteria in AD research. (A) Overall distribution of diagnostic frameworks across studies. (B) Trends in the adoption of each criterion over time.
NINCDS–ADRDA. In the studies that used the NINCDS-ADRDA criteria, 83% (33 out of 40) applied them exclusively: 25 (76%) focused on diagnosing mild to moderate AD,52–56,58–60,62–70,72–74,76,83,85,86,91 7 on mild AD,40,41,43–46,92 and 1 on mild or mild to moderate stages. 51 The remaining 7 studies combined NINCDS-ADRDA with other criteria: 2 paired it with DSM-IV for mild to moderate AD,78,81 2 with DSM-IV-TR for similar stages,71,87 and 1 for prodromal AD. 25 Moreover, 1 study integrated NINCDS-ADRDA with NIA-AA 2011 for mild AD, 47 while another combined NINCDS-ADRDA, NIA-AA 2011, and DSM-5 for mild to moderate AD diagnosis. 84
NIA–AA. The NIA–AA (2011) criteria represented a significant advancement in AD diagnostics by covering preclinical AD, MCI due to AD, and AD dementia,11,93,94 applicable in both clinical and research settings. In our analysis, 4 studies used the AD dementia criteria 11 for diagnosing mild to moderate AD,61,79,82,88 while 3 for mild AD.21,42,50 There studies applied the MCI due to AD criteria 93 to identify MCI or mild AD.35,39,49 In addition, 8 studies combined MCI due to AD criteria with the AD dementia criteria: 6 targeted MCI or mild AD,33,34,36–38,95 and 2 focused on prodromal to mild AD.31,32 Notably, only one study used NIA-AA 2018 research framework 12 for diagnosing mild to moderate AD in 2024. 89
IWG. The IWG criteria were the first to include pathological biomarkers in AD diagnosis, emphasizing clinical symptoms as primary and biomarkers as supplementary. 96 This contrasts with the America Association Group criteria, which prioritize biomarkers. 13 This study shows that the IWG criteria are infrequently applied in clinical research. IWG-1 and IWG-2 are both mainly used for diagnosing prodromal or mild AD (n = 6),24,26–30 with one study also using IWG-2 for diagnosing mild to moderate AD. 77
DSM-IV, DSM-IV-TR, and DSM-5. The common diagnostic characteristics of AD in DSM-IV, DSM-IV-TR, and DSM-5 include the presence of significant cognitive impairment, memory loss, functional decline, and the exclusion of other potential causes. However, early-stage AD cannot be diagnosed based solely on these criteria. In our studies, two investigations employed DSM-IV exclusively for diagnosing mild to moderate AD,57,75 while one study used DSM-5 for the same purpose. 80 Two studies utilized the NINCDS-ADRDA criteria in conjunction with DSM-IV-TR for diagnosing mild to moderate AD,71,87 and one study applied the same approach for diagnosing prodromal AD. 25 One study combined the Peterson criteria for MCI 23 with DSM-IV-TR for dementia exclusion in the diagnosis of prodromal AD. 22 Furthermore, one study integrated the NINCDS-ADRDA criteria with DSM-5 and the 2011 NIA-AA criteria for diagnosing mild to moderate AD. 84
Disease states
Overview. From the NIA–AA (2011) criteria, AD is recognized as a continuous disease process, with distinct clinical features and varying degrees of cognitive impairment at each stage. 94 According to the 2020 Alzheimer's Association report, AD is further categorized into five stages: preclinical AD, MCI due to AD, and mild, moderate, and severe AD. 97 In this review, we found that the majority of studies (56%, n = 40) focused on the mild to moderate stages of AD, followed by studies on mild AD (16%, n = 11). MCI or mild AD accounted for 13% (n = 9), while prodromal AD and prodromal to mild AD accounted for 8% (n = 6) and 6% (n = 4), respectively. Only one study specifically investigated moderate to severe stages of AD. Moreover, as early diagnostic approaches continue to develop, research is increasingly focusing on the early stages of the disease. The distribution of research stages is shown in Figure 4.

Selection of AD stages in research. (A) Proportional representation of studies focusing on different disease phases. (B) Temporal trends in research targeting various AD stages.
AD dementia stage. The mild-to-moderate AD stage is the most commonly studied disease state in our research, with the majority of studies focusing on drug development. Of these studies, 5 targeted Phase III trials,53,60,61,63,87 1 targeted Phase IIb, 58 1 focused on Phase II-III, 88 9 on Phase II,65,67,68,70,79,80,82,89,91 and 1 on Phase I. 69 Most interventions at this stage did not result in significant improvements in cognitive function, like humanized monoclonal antibody60,67,82,98; omega-3 fatty acids 55 ; inhibitor of the receptor for advanced glycation end products 56 ; α7 nicotinic acetylcholine receptor agonist 58 and virgin coconut oil. 86 Only 5 studies reported positive outcomes,38,80,81,83,85 while three observed a reduction in cognitive decline.24,77,78 Additionally, one study investigating donepezil for the treatment of moderate to severe AD also yielded negative results. 90
Early AD stage. We found a total of 11 studies focused on mild AD,40–50 6 on prodromal AD,22,24–28 4 on both prodromal and/or mild AD,29–32 and 9 on MCI due to AD or mild AD.21,33–39,95 We observed that many studies on the early stages of AD also reported negative results, such as transcranial direct current stimulation, 41 humanized monoclonal antibody,31,44 phosphodiesterase 9 inhibitor. 29 And some drugs even accelerate cognitive decline.22,25 Meanwhile, 7 studies did find a reduction in disease progression, including aducanumab, 34 donanemab, 30 lecanemab, 95 LipiDiDiet, 24 multimodal lifestyle intervention with medical food, 27 glutamate modulator, 47 and polyphenol chemical. 26 However, only 8 studies showed cognitive function improvement, including intensive lifestyle changes, 38 personalized rTMS. 21 aerobic exercise, 45 medium chain triglyceride oil, 78 combined metabolic activators, 80 boswellic acids, 81 sodium benzoate. 83 and fenugreek seed extract supplementation. 85 These results suggest that monotherapy yields minimal cognitive benefits in early-stage AD.
Cognitive assessment scales
Overview. Neuropsychological assessment scales are vital in clinical neurology and research, helping to evaluate the nature and extent of cognitive impairments caused by brain lesions, identify the affected cognitive domains, and determine the severity of cognitive dysfunction. 99 We have sorted and summarized the types of cognitive assessment scales and the MMSE cutoff points for each stage of AD. The analysis revealed considerable variation in the cognitive assessment scales used, with MMSE being the most frequently cited in research. However, the MMSE cutoff points showed significant variability, as illustrated in Figure 5.

Use of cognitive assessment tools. (A) Prevalence of different cognitive function scales. (B) Variation in MMSE cutoff scores across AD stages.
Type of cognitive assessment scales. The MMSE, first introduced in 1975, is a widely used neuropsychological tool primarily designed to assess cognitive function and aid in the diagnosis of dementia and other neurological disorders. 100 Our review found that the vast majority of studies (86%, n = 61) used the MMSE as part of their cognitive assessment protocols (Figure 5A). Of the remaining studies, Montreal Cognitive Assessment (MoCA), 38 Clinical Dementia Rating (CDR),50,85 Geriatric Depression Scale (GDS), 88 and ADAS-cog 80 were often preferred, with one study not using any screening scale. 78 Among the MMSE-based studies, 43% (n = 26) used MMSE scores as the sole cognitive assessment screening scale,24,26,28,30,33,40,41,43–45,47,51,59,62,63,65,66,69,71,72,74,75,79,86,87,101 while 21 studies incorporated CDR or CDR-SB,22,29,31,32,34–37,39,48,49,55,61,67,70,77,81–84,90 7 combined it with the Rosen Modified Hachinski Ischemic Score (RMHIS),35,53,54,56,60,73,76 and 2 used it alongside the Geriatric Depression Scale (GDS).42,89
MMSE cutoff points. Our analysis reveals that MMSE score definitions varied across different stages of the disease (Figure 5B). For the mild to moderate stages of AD, MMSE cutoff points exhibited the greatest variability, with 19 distinct types identified: the most commonly used ranges were 15–26 (n = 5)55,69,71,74,79 and 18–26 (n = 5),65,67,70,77,89 then followed by 14–26 (n = 4)54,56,61,73 and 16–26 (n = 3)53,60,63; while 20–26,51,57 12–26,64,101 and 10–2681,83 were reported in 2 studies each. The remaining 12 cutoff ranges appeared in only one study each, with the lowest cutoff set at 1062,68,84 and the highest at 28.59,76 For mild AD, 7 cutoff types were identified: 22–30 (n = 5),32,35–37,43 20–30 (n = 4),31,40,42,45 20–26 (n = 3),44,48,51 18–30 (n = 2),21,41 19–27 (n = 1), 47 20–28 (n = 1), 30 and 20–27 (n = 1). 49 For prodromal AD, four cutoff ranges were used: 24–30 (n = 7),22,24–29 22–30 (n = 1), 32 20–28 (n = 1), 30 and 20–30 (n = 1). 31 In the case of MCI due to AD, four cutoff types were also observed: 22–30 (n = 3),35–37 21–30 (n = 1), 33 24–30 (n = 1), 34 and 17–30 (n = 1). 39 While moderate to severe AD was classified with a range of 0–20 (n = 1). 90
Biomarkers and neuroimaging examination
Biomarkers and neuroimaging are essential for the early and accurate diagnosis of AD, as they detect pathological changes before symptoms appear and provide objective evidence to support clinical assessments. In our included studies, 38% conducted AD-related biomarker testing, 20% utilized neuroimaging methods consistent with AD diagnosis, and 42% used neither approach (traditional symptom-based diagnosis) (Figure 6A). Of the studies focused on AD pathology, 6 used CSF testing to confirm amyloid positivity,22,33,39,49,77,89 7 employed PET imaging,25,26,34,35,48,62,70 and 15 used either CSF or PET or MRI for biomarker pathology positivity.4,21,24,27,29–32,36,37,42,44,50,61,82 For neuroimaging techniques, 7 studies incorporated MRI or CT to support an AD diagnosis,46,56,64,65,71,75,76 and 5 studies relied on MRI findings consistent with AD.53,60,63,73,88 And one utilized FDG-PET to exclude other types of dementia. 47 Moreover, in recent years, the use of biomarkers has increased, possibly driven by the growing number of studies focusing on early-stage AD, as shown in Figure 6B.

Integration of biomarkers in AD research. (A) Overview of the use of pathological biomarkers, neuroimaging techniques, and clinical symptom-based diagnostic approaches. (B) Annual trends in studies incorporating biomarkers and neuroimaging. (C) Distribution of the minimum age of participants across included studies.
Age range
The prevalence of AD increases significantly with age, affecting approximately 3%, 17%, and 32% of individuals aged 65–74, 75–84, and ≥85 years, respectively. 102 Nevertheless, AD dementia is not an inevitable consequence of aging nor solely caused by advanced age. 103 The NINCDS-ADRDA criteria indicate AD onset typically between ages 40 and 90, with incidence highest in those ≥65 years. 7 Similarly, ICD-10, DSM-IV, and DSM-IV-TR apply 65 years as the age threshold for differentiating early from late AD.
The studies included in this review displayed diverse age range definitions, even for the same disease stage, with 30 distinct ranges identified. For the mild to moderate AD stage, 9 studies included participants aged ≥50 years,26,51,59,64,72,78,80,87,88 5 used ≥55 years,55,56,73,76,79 and 3 applied the 50–85 range.69,82,89 For mild AD, 2 studies used the 50–90 range,45,46 while other ranges spanned from a minimum age of 45 50 to a maximum of 95. 47 In prodromal AD, 2 studies reported using the 55–85 range,24,25 another 2 used 60–85,27,28 while individual studies adopted 45–90 22 and 54–75 26 ranges. For MCI due to AD or mild AD, 2 studies used the 50–90 range,4,37 while others included 45–90, 38 50–80, 36 50–85, 34 51–85, 33 55–89, 39 and 55–90, 21 with each range reported in a single study. Among all studies, ages 45, 50, 55, and 60 were the most common starting points, as shown in Figure 6C.
Discussion
Diagnostic criteria in clinical research
Accurate diagnostic and inclusion criteria are fundamental to ensuring the validity and comparability of RCTs in AD. 104 Our analysis reveals that the NINCDS–ADRDA criteria, despite being developed four decades ago, remain widely used in clinical research, particularly for mild-to-moderate AD. The NIA–AA (2011) criteria, which cover all AD stages, are also extensively applied. Meanwhile, the DSM-IV, DSM-IV-TR, and DSM-5 criteria primarily focus on diagnosing Alzheimer's-type dementia and are often supplemented with additional criteria to rule out other neurodegenerative and psychiatric disorders. However, the adoption of biomarker-based frameworks, such as IWG and NIA–AA (2018), remains limited in clinical trials.
The symptom-based diagnostic criteria, including NINCDS-ADRDA, ICD-10, DSM-IV, DSM-IV-TR, and DSM-5, are categorized as first-generation criteria, 105 valued for their simplicity and ease of use but limited to diagnosing AD dementia, as they cannot identify early AD. Second-generation criteria, including the IWG and NIA-AA series, improve diagnostic accuracy by incorporating biomarker-based diagnostics, allowing for early AD diagnosis. However, due to gaps in understanding AD pathogenesis and limitations in biomarker detection technologies during earlier years, their initial implementation was constrained. The latest third-generation criteria incorporate blood-based biomarkers, 13 marking a new era of non-invasive AD screening and simplifying the diagnostic process. A detailed comparison of the advantages and limitations of each diagnostic framework is provided in the Supplemental Material.
Cognitive assessment: applications and limitations
Cognitive assessment scales play a vital role in AD screening and diagnosis. The MMSE remains the most widely used tool, appearing in 86% of reviewed studies due to its ease of administration and ability to differentiate dementia from normal cognition. 106 However, 37% of studies relied solely on MMSE, despite evidence that it lacks sensitivity in detecting early-stage AD. 107 Moreover, the MMSE has been criticized for its limitations in detecting mild dementia and MCI, particularly due to its uneven assessment of cognitive domains and low sensitivity to executive function deficits. 108 Research has shown that MMSE fails to reliably detect cognitive decline in highly educated individuals, while also overestimating impairment in individuals with lower education levels. 109 Given these limitations, relying solely on MMSE may lead to misclassification of patients, including the incorrect inclusion of non-AD participants in clinical trials, thereby affecting study accuracy and reproducibility. Multidomain assessments, such as incorporating CDR, ADAS-cog, or ADL, have been shown to improve sensitivity in early AD detection and enhance disease stratification in clinical research. 110
The MMSE cutoffs lack a standardized criterion and are influenced by factors such as age, education level, and cultural background of the assessed population. 109 Our analysis found that 26 is the most commonly used threshold for defining cognitive impairment.29,44,48,51,60,61,63,67,71 Other frequently used cutoffs include 24,22,24–26,29 as well as 2235,43 and 20 points. 62 Interestingly, higher cutpoint like 27 47 and 28 30 have been utilized in some studies. For mild to moderate AD, we found a remarkable diversity, with 19 distinct cutoffs reported across different studies. This indicates that the variability in using MMSE for disease stratification is substantial, potentially leading to difficulties in comparing and replicating research results. Therefore, more objective assessment methods are needed to address the limitations of the MMSE scale.
Advances and challenges in biomarker-based diagnosis
The integration of biomarkers has improved AD diagnostic accuracy, yet their use in RCTs remains inconsistent. Our review found that less than forty percent of studies incorporated biomarkers, with nearly half relying exclusively on traditional clinical assessments (Figure 6A). The limited adoption of biomarkers may be caused by the collection carries risks and discomfort for CSF, and expensive for PET imaging. Moreover, both methods may not effectively detect early cognitive decline, can lead to over-diagnosis, and offer limited prognostic value as not all patients with abnormal biomarkers progress to AD.111,112 In addition, although MRI is frequently used in clinical practice for the diagnosis of AD, particularly features such as medial temporal lobe atrophy, hippocampal atrophy, hippocampal volume loss, enlarged lateral ventricles, cortical thinning, and posterior cortical atrophy, these abnormalities typically emerge when the disease has already progressed to the dementia stage. 113 So CSF, PET and MRI all have limited utility for early screening of AD. We need to develop noninvasive, straightforward, and cost-effective screening methods, such as blood biomarkers or electroencephalography (EEG).
In recent years, plasma phosphorylated tau biomarkers, particularly p-tau 217, have emerged as a major breakthrough in AD diagnostics. Studies have shown that p-tau 217 has diagnostic accuracy comparable to CSF and PET biomarkers in detecting early AD pathology. 114 Compared to p-tau 181, p-tau 217 demonstrates higher specificity in distinguishing AD from other neurodegenerative diseases and correlates strongly with Aβ burden and neuronal degeneration. 115 Moreover, p-tau 217 detection is less invasive and more cost-effective than CSF and PET, making it a promising tool for early screening, disease monitoring, and patient stratification in clinical trials.
In parallel, EEG-based biomarkers are gaining recognition for early AD diagnosis. 116 EEG provides real-time insights into brain activity, making it a promising tool for detecting synaptic dysfunction in early AD. 117 Altered EEG patterns, such as increased delta/theta power and reduced global field synchronization, correlate with CSF Aβ42, p-tau, and t-tau levels. 118 Furthermore, increased theta/gamma and alpha3/alpha2 ratios in MCI patients are associated with higher AD conversion rates.119,120 The Electrophysiology Professional Interest Area (EPIA) and Global Brain Consortium endorsed recommendations suggest that resting-state EEG can provide objective electrophysiological evidence for early screening, disease progression monitoring, and treatment evaluation of AD. 121 They also proposed a new ATPN diagnostic framework for AD, where P represents electrophysiological biomarkers provided by EEG. 121 Given its low cost, accessibility, and high temporal resolution, EEG could also serve as a valuable complement to cognitive assessments and biomarker-based diagnostics.
Therapeutic strategies and future directions
For AD treatment, it is widely recognized that earlier intervention leads to better therapeutic outcomes. However, both earlier studies targeting mild-to-moderate AD and recent research focusing on early-stage AD, including prodromal AD, MCI due to AD, and mild AD, have predominantly investigated interventions such as anti-Aβ monoclonal antibodies,37,53,58–60,67,70 Aβ inhibitors,25,32,54 tau-aggregation inhibitors,49,61 and anti-tau monoclonal antibodies,31,35,36,82 yet none have shown significant cognitive improvement.
In recent 10 years, only aducanumab, lecanemab, and donanemab have received FDA approval for slowing cognitive decline in MCI and mild AD.5,34,95 However, the clinical efficacy of these drugs is limited and associated with serious adverse effects, even after 18 months of treatment, which are far less pronounced than 6 months of oral 10 mg donepezil treatment. 122 Meanwhile, a recent meta-analysis reported that rTMS demonstrated greater efficacy, better tolerability, and fewer side effects than the current three DMT drugs. 123 In particular, a personalized rTMS protocol administered over four weeks (20 sessions) for early-stage AD patients resulted in significant improvements in both cognitive function and daily performance. 21 Furthermore, some studies suggests that multimodal strategies, such as the RECODE program,124,125 lifestyle or dietary changes may outperform single-drug therapies.28,38,126 These non-invasive, low-risk interventions merit further exploration to evaluate their potential role in AD management.
Study limitations
This systematic review has several limitations that should be acknowledged. First, the reliance on three databases (Web of Science, PubMed, and Google Scholar) may have excluded relevant studies indexed in other databases, such as Embase or Scopus, potentially introducing selection bias. Second, although 27,471 articles were initially screened, only 71 studies met the inclusion criteria, which may limit the generalizability of the findings, particularly for underrepresented populations or research methodologies. Third, the broad time span of included studies (2014–2024) may have contributed to the limited adoption of more recent diagnostic frameworks, such as IWG-2021 and NIA-AA 2018, which integrate biomarkers more comprehensively. Since older studies relied heavily on symptom-based criteria (e.g., NINCDS-ADRDA, NIA-AA 2011), the review may underrepresent emerging biomarker-driven diagnostic approaches, leading to a potential bias toward traditional clinical diagnostic methods.
Conclusion
Our review summarized the diagnostic and detailed inclusion criteria adopted in clinical studies of AD in the past 10 years, mainly concluded as follows: (1) The NINCDS–ADRDA criteria are the most prevalent used to diagnose advanced AD, the less commonly used NIA–AA (2011) criteria encompass a wider range of AD stages; (2) Earlier studies primarily focused on mild-to-moderate AD, but recent years have seen an increase in research on early-stage AD. However, most single-drug therapies or standalone interventions have failed to produce significant cognitive improvements at either early or advanced stages of AD dementia; (3) The MMSE remains the most widely used cognitive assessment tool for AD screening, but its cutoff points vary considerably across studies; (4) The use of biomarkers in clinical research is limited, with many studies relying on traditional clinical methods; (5) The age ranges for study inclusion varied, most studies focused on participants aged 50 to 90 years. Our findings emphasize the need for harmonizing AD diagnostic criteria and explore combination therapies for AD treatment. Non-invasive and low-risk interventions deserve more attention, while more objective and practical cognitive assessment tools, such as blood biomarker and EEG, could serve as valuable supplements to traditional cognitive scales.
Supplemental Material
sj-docx-1-alr-10.1177_25424823251362444 - Supplemental material for Diagnostic and inclusion criteria in Alzheimer's disease clinical trials: A systematic review of the past decade
Supplemental material, sj-docx-1-alr-10.1177_25424823251362444 for Diagnostic and inclusion criteria in Alzheimer's disease clinical trials: A systematic review of the past decade by Yumei Liu, Siyan Chen, Sha Li, Zian Pei, Shuhan Fan and Yi Guo in Journal of Alzheimer's Disease Reports
Footnotes
Author contributions
Funding
This review was supported by National Natural Science Foundation of China (82371471), the Shenzhen Science and Technology Innovation Commission (KCXFZ20201221173400001, KCXFZ20201221173411032, and SGDX20210823103805042) and Natural Science Fund of Guangdong Province (2021A1515010983).
Declaration of conflicting interests
The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.
Data availability statement
Data supporting the findings of this study are available in this article. Further inquiries can be directed to the corresponding authors.
Supplemental material
Supplemental material for this article is available online.
References
Supplementary Material
Please find the following supplemental material available below.
For Open Access articles published under a Creative Commons License, all supplemental material carries the same license as the article it is associated with.
For non-Open Access articles published, all supplemental material carries a non-exclusive license, and permission requests for re-use of supplemental material or any part of supplemental material shall be sent directly to the copyright owner as specified in the copyright notice associated with the article.
