A 70-year-old patient with no psychiatric history presents to your office complaining of memory problems. The patient frequently misplaces items, forgets appointments, and has difficulty completing tasks. You observe that the patient interrupts you frequently and misinterprets your instructions during cognitive screening. The patient is concerned about having dementia. That’s on your differential, but could it be attention-deficit/hyperactivity disorder? Even in an older patient, it’s worth considering.
Until recently, attention-deficit/hyperactivity disorder (ADHD) was considered primarily a disorder of childhood and adolescence. The modern conceptualization of ADHD originated in the mid-19th century, largely because of political and societal changes that made formal, classroom-based schooling accessible to many more children (Atten Defic Hyperact Disord. 2014;6[3]:125-51). Although symptoms must cause dysfunction in two or more settings to meet DSM-5 criteria for the disorder, ADHD remains best understood as a classroom problem.
Dr. Kalya Vardi
A growing body of evidence, however, reveals that ADHD symptoms persist into adulthood in two-thirds of cases (J Atten Disord. 2015 Sep 22. pil: 1087054715604360); (Psychol Med. 2015 Jan 23;1-12). Older adults might be especially prone to misdiagnosis given that they and their clinicians might be more concerned about the possibility of a neurodegenerative disorder.
The DSM-5 clearly defines ADHD as a neurodevelopmental disorder that begins in childhood. Nonetheless, the manual says that ADHD can be diagnosed retrospectively in adults who have at least five inattentive or hyperactive symptoms (compared with six or more for children) and who recall having “several” inattentive or hyperactive symptoms prior to age 12. ADHD symptoms attenuate in adulthood. Remission rates vary considerably across studies, but even among adults who no longer meet criteria for the diagnosis, residual symptoms are common and continue to interfere with functioning (Psychol Med. 2006;36:159-65); (Psychol Med. 2015;23:1-12); (J Atten Disord. 2015 Sep 22). Inattentive symptoms are more likely to persist than hyperactive-impulsive symptoms (Atten Def Hyperact Disord. 2015 Jun 12).
To date, little research has focused on ADHD symptoms in the geriatric population. Investigators of a recent cohort study of noninstitutionalized Dutch adults over 60 years old estimate that the prevalence of ADHD in this population is 2.8% with an additional 1.4% reporting functional impairment because of subsyndromal disease (Br J Psychiatry. 2012 Oct;201[4]:298-305).
Dr. Ellen Lee
Since attention is requisite to virtually all cognitive tasks, inattention can negatively affect functioning in a variety of ways. Patients and clinicians could easily misinterpret inattentive symptoms as deficits in other cognitive domains, such as memory. A thorough developmental history should clarify the diagnosis by identifying whether or not cognitive symptoms were present in childhood. Standardized scales, such as the Wender Utah Rating Scale and the Barkley Childhood Symptoms Scale, can help clinicians elicit a history of childhood ADHD symptoms and assess the validity of retrospective self-reports. Since inattention is a nonspecific symptom, the differential diagnosis also should include depression, anxiety, and delirium, among others.
Neuropsychological testing can clarify the diagnosis by quantifying patient performance across cognitive domains, comparing patient performance to normative data, and controlling for motivational factors. The pattern of cognitive deficits is well established and unique for most forms of dementia in their early stages. For example, rapid forgetting is the “first and worst” symptom of Alzheimer’s disease, the most common form of dementia. Attention typically is the next cognitive domain affected in Alzheimer’s disease, preceding visuospatial and language involvement (Brain. 1999 Mar;122[Pt. 3]:383-404). As dementias progress and more cognitive domains are affected, neuropsychological testing might be less helpful in differentiating dementias from each other and teasing out comorbidities such as ADHD, depression, anxiety, and substance use disorders. From another perspective, preexisting ADHD exacerbates cognitive deficits, impairing function and mimicking more advanced neurodegenerative disease. Therefore, identifying and treating comorbid ADHD may improve functioning in patients with dementia.
ADHD and Alzheimer’s disease might share some pathophysiologic mechanisms. Dysregulated cholinergic and noradrenergic activity have been observed in both conditions (Science. 2000 Dec 22;290[5500]:2315-9; (J Neuropathol Exp Neurol. 2011 Nov;70[11]:960-9). Research also suggests that cholinesterase inhibitors might disproportionately slow the decline of attention in Alzheimer’s disease, relative to their effects on disease progression in other cognitive domains (J Alzheimers Dis. 2014;40[3]:737-42). However, small case-control studies have not shown an association between ADHD and Alzheimer’s disease, and cohort studies in the elderly are lacking (Eur J Neurol. Jan;18[1]:78-84); (J Aging Res. 2011;2011. doi:10.4061/2011/729801).
Though ADHD affects a relatively small proportion of the elderly population, it presents a unique challenge when evaluating patients for suspected neurodegenerative disorders. Clinician awareness, detailed history-taking, and neuropsychological testing are essential to diagnosing ADHD in the geriatric population. Appropriate treatment of ADHD might improve functional outcomes for patients, including those with comorbid dementia. Although ADHD and Alzheimer’s disease have some neurobiologic similarities, further research is needed to clarify how these disorders interact, both biologically and clinically.