Adult ADHD: Risk Factor for Dementia or Phenotypic Mimic?

Brandy L. Callahan,Daniel Bierstone,Donald T. Stuss,Sandra E. Black

doi:10.3389/fnagi.2017.00260

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.

Highlights

Attention-deficit hyperactivity disorder (ADHD) is a neurodevelopmental disorder characterized by cognitive deficits and/or behavioral disturbances
Considered exclusively a childhood disorder, it is recognized that in 40–60% of cases, symptoms persist into adulthood and old age ADHD and mild cognitive impairment (MCI)
We propose that future work should aim, in particular, to clarify how ADHD and MCI differ in terms of specific executive functions

Summary

Introduction

Attention-deficit hyperactivity disorder (ADHD) is a neurodevelopmental disorder characterized by cognitive deficits (inability to sustain attention) and/or behavioral disturbances (inability to regulate motor behavior). Current criteria (American Psychiatric Association, 2013) include guidelines for diagnosing adults with ADHD; symptom onset must necessarily have occurred in childhood. Memory problems have been reported in adult ADHD, manifesting primarily as complaints of forgetfulness (Rosler et al, 2010). These symptoms can be explained by impaired frontal-lobe functioning, as the frontal cortex is well-known to be involved in memory encoding and retrieval processes (Moscovitch and Winocur, 2002)

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