Adult ADHD: Risk Factor for Dementia or Phenotypic Mimic?

Abstract

Attention-deficit hyperactivity disorder (ADHD) has historically been considered a disorder of childhood and adolescence. However, it is now recognized that ADHD symptoms persist into adulthood in up to 60% of individuals. Some of the cognitive symptoms that characterize ADHD (inability to provide sustained attention or mental effort, difficulty organizing or multi-tasking, forgetfulness) may closely resemble symptoms of prodromal dementia, also often referred to as mild cognitive impairment (MCI), particularly in patients over age 50. In addition to the overlap in cognitive symptoms, adults with ADHD and those with MCI may also share a number of behavioral and psychiatric symptoms, including sleep disturbances, depression, and anxiety. As a result, both syndromes may be difficult to distinguish clinically in older patients, particularly those who present to memory clinics with subjective cognitive complaints and fear the onset of a neurodegenerative process: is it ADHD, MCI, or both? Currently, it is unclear whether ADHD is associated with incipient dementia or is being misdiagnosed as MCI due to symptom overlap, as there exist data supporting either possibility. Here, we aim to elucidate this issue by outlining three hypothetical ways in which ADHD and MCI might relate to each other, providing an overview of the evidence relevant to each hypothesis, and delineating areas for future research. This is a question of considerable importance, with implications for improved diagnostic specificity of early dementia, improved accuracy of disease prevalence estimates, and better identification of individuals for targeted treatment.

Examining the validity of the ADHD concept in adults and older adults

“…Up to 40% of adult ADHD cases persist into old age, and prevalence rates may reach 3-4% in seniors. 5,6 However, these cases are often unrecognized 19 or misdiagnosed, 20 likely in part because our current understanding of how ADHD symptoms present in older adults, relative to younger patients, is sorely lacking.…”

A model of lipid dysregulation and altered nutrient status in Alzheimer's disease

“…Then, these individuals could be followed up for several decades to test the second hypothesis that higher level of N 2 O exposures earlier in life increases AD risk in later life. Such data could clarify the question about whether these two conditions do, in fact, represent a possible continuum of brain degeneration over the lifespan [71] , perhaps due to chronic exposure to environmental N 2 O. Related to this line of inquiry, we recommend that further study specifically focus on the presence of the aforementioned AD changes in early neuropsychiatric correlates of AD.…”

Genetic Variants and Functional Pathways Associated with Resilience to Alzheimer’s Disease

“…Interestingly, genetic risk for OCD was associated with higher resilience scores, while genetic risk for ADHD was associated with lower resilience. Although there is some literature suggesting a potential link between ADHD and dementia, it is challenging because of the symptomatic overlap of the two conditions in adulthood (Callahan et al, 2017). Even less work has characterized the association between OCD and dementia, but the limited literatures suggests OCD is a risk factor for dementia (Dondu et al, 2015).…”