Study: Mild Cognitive Impairment and ADHD Uniquely Impair Older Adults
Though the symptoms of ADHD and mild cognitive impairment overlap in older adults, a new study found that they impair distinct areas of the brain, and called into question the purported link between ADHD and dementia.
January 26, 2022
Memory is impaired in both older adults with ADHD and those with mild cognitive impairment (MCI). However, distinctions do exist; those with MCI experience a storage deficit (indicated by relatively smaller hippocampi) and those with ADHD encounter an encoding deficit (indicated by frontal lobe thinning.) This finding comes from a new study published in the Journal of Attention Disorders that also found reason to question previous findings that ADHD may be a risk factor for dementia.1
ADHD is not well-recognized in older adults, in part because patients’ cognitive difficulties are often mistaken for MCI. To establish the shared and unique cognitive and imaging characteristics of older adults with ADHD or MCI, participants from a cognitive neurology clinic (40 with ADHD, 29 with MCI, and 37 controls) underwent neuropsychological assessment by a team of researchers from the University of Calgary and University of Toronto.
Older adults with ADHD and those with MCI both displayed normal executive functioning. Participants with ADHD performed similarly to controls in a context with added semantic structure, indicating a frontally mediated encoding deficit in ADHD and a temporally mediated storage deficit in MCI. Only participants with MCI showed robust semantic retrieval deficits. Additional brain differences included reduced hippocampal volumes in MCI (potentially indicating a primary storage memory deficit), and cortical thinning in the middle frontal gyrus for ADHD, which impacts working memory abilities.
Previous literature has speculated that ADHD may be a risk factor for dementia. Researchers concluded that, although both disorders display dementia-like features, “the pathological processes underlying ADHD and MCI are fundamentally distinct, and that their putative association in prior work is more parsimoniously explained by ADHD mimicking the MCI phenotype.”
Differentiating the symptoms of ADHD from those of MCI in older adults is relevant to clinical practice, say the researchers, and needed to inform diagnostic impressions and improve clinical services to older adults.
1 Callahan BL, Ramakrishnan N, Shammi P, et al. Cognitive and Neuroimaging Profiles of Older Adults With Attention Deficit/Hyperactivity Disorder Presenting to a Memory Clinic. Journal of Attention Disorders. November 2021. doi:10.1177/10870547211060546