Diagnostic Cohorts

While Alzheimer’s disease is a continuum of biological and symptomatic changes, clinical diagnosis and categorization is commonly used in practice and is applied to the ADNI study cohort.

Diagnostic criteria are based on the results of well-validated clinical assessments including participant performance in the clinical dementia rating (CDR), Mini Mental State Exam (MMSE), performance on the Wechsler Logical Memory II paragraph recall test (part of the neuropsychological battery), and the judgement of the clinicians.

There are three diagnostic cohorts that have been relatively consistent throughout the history of the study, as well as three diagnostic cohorts that were present historically but are no longer used and are described below.

  • The Cognitively Unimpaired (CU) cohort - also called Cognitively Normal (CN) and Normal Control (NL) in certain contexts - is comprised of individuals who do not present significant evidence of cognitive impairment during their screening assessment.

    During the ADNI2 phase, this cohort was further subdivided into the Subjective Memory Complaint (SMC) cohort, consisting of participants who had subjective complaints of memory change and/or cognitive decline, but did not reach the diagnostic criteria for impairment.

    SMC participants who chose to roll over into the ADNI3 phase and did not meet the criteria for MCI were reassigned into the CN cohort. There is no separate SMC cohort after ADNI2.

  • The Mild Cognitive Impairment (MCI) cohort represents an intermediate stage in the progression to dementia. These participants do not meet the diagnostic criteria for AD/dementia cohort but still present clinically relevant cognitive impairment.

    During the ADNIGO and ADNI2 Phases of the study, the MCI cohort was divided into Early MCI and Late MCI (EMCI and LMCI respectively) cohorts, based on the severity of their symptoms. This classification scheme was dropped following ADNI2 and all MCI participants including early and late are categorized as MCI in subsequent phases.

  • The Early-Stage Alzheimer’s Disease (AD or DEM) cohort consists of individuals who clinically present with Alzheimer’s disease or some related dementia.

    Screening criteria are in place to exclude prospective participants in the dementia arm whose symptoms likely arise from a non-Alzheimer’s etiology, such as severe cerebrovascular disease (stroke), Frontotemporal dementia (FTD), or Parkinson’s disease (PD).

A detailed list of the diagnostic criteria used to define cohorts in each phase of the study, excerpted from the procedures manuals, is presented below: