Distinct Cognitive and Neuroimaging Profiles in Later-Life Attention Deficit/Hyperactivity Disorder and Mild Cognitive Impairment

Abstract

Background: Attention deficit/hyperactivity disorder (ADHD) is increasingly being recognized in adults and older adults. Some of its behavioral features (e.g., distractibility, forgetfulness, impulsivity) may resemble those of mild cognitive impairment (MCI), which contributes to diagnostic uncertainty in later life. The present study aimed to systematically compare ADHD and MCI on measures of cognition and structural neuroimaging to clarify the extent of their overlap (i.e., cognitive features of ADHD that are most likely to be taken for signs of MCI) and identify potential features unique to each disorder (i.e., that may be used to guide diagnostic impressions). Methods: One hundred and six adults aged 50 years or above were recruited from a Cognitive Neurology clinic (40 ADHD, 29 MCI and 37 controls) completed a comprehensive neuropsychological battery. A subsample (n=80) underwent structural neuroimaging.Results: Memory was impaired in both patient groups, but reflected a storage deficit in MCI (supported by imaging findings of reduced hippocampal volumes) and an encoding deficit in ADHD (supported by frontal-lobe cortical thinning). Both groups performed normally on executive measures. Semantic retrieval was uniquely impaired in MCI.Conclusions: Behavioral and structural imaging features strongly suggest that ADHD and MCI are similar manifestations of separate pathophysiological processes. Although ADHD has been proposed as a risk factor or prodromal stage of neurodegeneration, we propose it is rather acting as a phenotypic mimic of MCI via overlap in memory and executive performance.

Mild Cognitive Impairment or Attention-Deficit/Hyperactivity Disorder in Older Adults? A Cross Sectional Study

“…It has been presumed that poor memory strategy selection in those individuals due to a disrupted phonological loop may lead to inefficient encoding of the material to be learned. With the deficient conversion of verbal stimuli into memory, performances in tasks involving retrieval of information both spontaneously and in response to verbal cues predictably fall below the average levels ( 39 , 41 ).…”

“…In addition, scores in executive function tasks were comparable between ADHD and MCI groups. Accordingly, previous reports suggested that severity of frontal-executive impairments in ADHD, whether inherent of the disorder or exacerbated by age-related cognitive decline, might be compatible with subtle, but measurable difficulties to perform everyday life activities, which might mimic MCI presentation ( 41 , 42 ). Longitudinal investigation of executive control in this diagnostic group may clarify about the contribution of aging to cognitive load and disability in ADHD.…”