Low Sensitivity of Neuropsychological Scales Hinder Detection of Potential Benefit of Treatments in Alzheimer's Disease: A Position Paper.

BACKGROUND: Despite the advent of Disease Modifying Therapies (DMTs) for Alzheimer's Disease (AD), the approval and commercialization of anti-amyloid monoclonal antibodies has been slow and contentious, particularly in Europe. The primary source of debate is the discrepancy between robust biological effects-namely, effective β-amyloid clearance-and modest clinical improvements, which, although statistically significant, often fail to reach the minimal clinically important difference (MCID) compared to placebo. METHODS: This paper highlights a confounding factor in the interpretation of the results of clinical trials: limited sensitivity of neuropsychological outcome measures. These tools, developed in the 1980s and only marginally updated, are not suited to detect subtle but meaningful cognitive changes in early disease stages. RESULTS: The ADAS-Cog, the most commonly used cognitive endpoint, suffers from a substantial ceiling effect, impairing its ability to capture cognitive decline over short durations in prodromal populations. Likewise, functional scales such as the CDR-SB are inherently insensitive in mild cognitive impairment (MCI), as functional independence is, by definition, preserved. Moreover, the use of composite multidomain scales with high baseline scores may mask domain-specific improvements, further limiting a drug's capacity to reach MCID thresholds. CONCLUSION: Methodological limitations risk undervaluing the therapeutic impact of treatment, particularly in trials targeting early or preclinical phases where changes are subtle and domain-specific. Urgent reconsideration of outcome measures is necessary to ensure accurate assessment of clinical efficacy and to avoid prematurely discarding potentially beneficial therapies.