The prevalence of ADHD in adults aged >=50 years is a question yet to be answered. In a large, epidemiological study by Kessler et al, the prevalence of ADHD in adults was estimated to be 4.4%. This important study did not include patients older than 44 years old. In contrast to this, in a European population-based study, 50% of the study sample was older than 45 years (range: 18-75 years), and the prevalence of ADHD in this sample was 1.0%-2.5%.
Some recent studies have investigated the prevalence of ADHD in adults aged >=50 years and found prevalence rates below the previous estimates for adult ADHD (Table 1). In a Dutch epidemiological study, 1,419 adult participants aged 55-85 years were studied. The prevalence of syndromatic ADHD was 2.8% and symptomatic ADHD was 4.2%. The results also showed that younger elderly adults (60-70 years) reported more ADHD symptoms than the older group (71-94 years). The Australian PATH Through Life Project also found that older-age adults (68-74 years) reported significantly lower levels of ADHD symptoms as measured by ASRS screener than middle-aged adults (48-52 years). Approximately 2.2% of the older-age adults met the suggested cut-off for the Adult ADHD Self-Report Scale (ASRS)-screener score that has been linked to a clinical diagnosis of ADHD, versus 6.2% in the middle-aged group.
In a Swedish population-based study of 2,500 persons aged 65-80 years, the authors found the prevalence of self-rated childhood ADHD to be 3.3%. A methodological problem in this study is the dependence on retrospectively experienced childhood symptoms recalled 50-70 years later. The risk for recall bias, and both under- and overestimation of symptoms, is probably high.
These three epidemiological studies indicate that the prevalence of ADHD symptoms appears to decline to 1.0%-2.8% in the oldest ages. Some authors discuss the impact of lower life length expectancy in patients with ADHD, due to greater rates of accidents, substance abuse, mood disorders, and other health issues, resulting in a relative decline of people with ADHD by age. The lack of age-appropriate diagnostic criteria for adult ADHD may also explain some of the apparent decline in ADHD prevalence in older adults, as discussed by several authors. Simon et al discuss in their meta-analysis the problem with validity of DSM criteria for diagnosing adult ADHD and assume that a strict use of the criteria may lead to an underestimation of the prevalence of ADHD in adults. Another factor is the occurrence of health-related issues in adults aged >=50 years, making the differential diagnostic assessment related to an ADHD diagnosis difficult. Examples of such issues are mild cognitive impairment (MCI), dementia, and other neurodegenerative disorders, increasing polypharmacy, sleep disturbances, chronic pain and other physical conditions, and impaired vision and hearing. Despite the lack of research on ADHD in adults aged >=50 years, and many unanswered questions about prevalence and persistence of ADHD throughout the life span, there is reason to believe that ADHD or residual ADHD persists into middle age and late adulthood in a large number of patients. A number of recent studies from different countries using national registers and prescription databases have shown that a growing number of patients aged >=50 years are assessed and treated for ADHD worldwide.
A systematic search was conducted in the databases Medline/PubMed and PsycINFO to identify studies regarding ADHD in adults aged >=50 years. Search terms were "ADHD AND older adults" published up to date. The resulting list of papers was screened to find papers for this review, and the reference lists in the relevant papers were further screened to find other papers of relevance.
The core symptoms of ADHD are persisting inattentiveness, impulsivity, and hyperactivity. Despite the persistence of symptoms, the presentation of symptoms will often change over the course of development. The overt signs of hyperactivity and impulsivity in children with ADHD will often decline with increasing age, while symptoms of inattentiveness often will continue unchanged. The motor hyperactivity in children with ADHD is in adults often replaced by an "inner" hyperactivity in the form of restlessness, excessive fidgeting and talking, inability to relax, and difficulty to sit quietly for long periods. Impulsivity in adulthood may appear as outbursts of anger, impatience, careless driving, and making decisions without thinking. Inattention will manifest as disorganization, forgetfulness, poor performance in planning and completion of tasks, task shifting, and time management. Because of this developmental change in symptom expression, many adults will not fully exhibit the criteria for the diagnosis, while still remaining significantly impaired.
In addition to the core symptoms, ADHD in adults is strongly associated with emotional dysregulation (ED). The concept of ED includes symptoms such as increased irritability, low tolerance for frustration and stress, and emotional lability. Recent research indicates, however, that ED is not as specific for ADHD as previously assumed.
ADHD in all ages is associated with the presence of psychiatric comorbidity. Studies have shown that comorbidity can have a negative impact on treatment outcome in ADHD across the life span. Recent studies indicate that psychiatric comorbidity mostly occurs during childhood and adolescence, and more seldom have onset after the age of 20 years. A recent study by Rasmussen et al suggests that living longer without receiving central stimulant (CS) treatment may lead to an increase in comorbid psychiatric problems. The comorbid disorders most strongly associated with adult ADHD are anxiety disorders, mood disorders, antisocial personality disorder, and substance use disorders.
Most studies of comorbidity in adult ADHD are done in samples of young adults up to 40 years. The developmental alteration of comorbid disorders into middle-aged and older samples is poorly understood. We have identified only a few studies presenting data on comorbidity in samples of adults aged >=50 years. A Dutch study, with average sample age 71 years (range: 60-94 years), found that participants with ADHD had more depressive and anxiety symptoms than participants without ADHD. In another paper presenting data from the same study, the authors found that older adults with ADHD had significantly lower self-esteem and sense of mastery, and higher levels of neuroticism and social inadequacy, than older adults without ADHD. Self-esteem and sense of mastery partly explained the association between ADHD and depressive symptoms. Semeijn et al found that the risk of depression in older adults with ADHD was partly explained by serious conflicts and adverse life events. In this study, lower cognitive functioning was also explained by depressive symptoms.
In a sample of adults aged >=50 years with ADHD from Norway (mean age: 55.7 years), 46.7% of the participants reported psychiatric comorbidity, depression 36.7%, anxiety 26.5%, and bipolar disorder 24.5%. The sample was recruited from the national ADHD organization, and not necessarily representative for adults aged >=50 years with ADHD. In a small study of 27 patients from the US, recruited from psychiatrists in private practice, 63% of the participants reported having other mental health conditions, depression 54%, anxiety 42%, and bipolar disorder 8%.
In the older population, the prevalence of dementia increases steadily with advancing age. MCI is a diagnosis designed as a predictor of prodromal degenerative dementia, and its prevalence in the geriatric population is estimated to 16%. MCI includes cognitive problems in older ages that do not meet the criteria for dementia, and results in no or minimal functional impairment. In a review by Ivanchak et al, the authors discuss the role of ADHD as a predisposing factor for MCI and more manifest degenerative disease in late life, but conclude that such an association is less than convincing. On the contrary, a clinical study from Argentina found an association between childhood ADHD and dementia with Lewy bodies, but not with Alzheimer's disease. The authors have no explanation for this association between ADHD and dementia with Lewy bodies, but discuss the role of dopaminergic dysfunction in both diseases.
There has been a growing interest in somatic comorbidity in ADHD. A number of somatic diseases have been found to have an association to ADHD in children, adolescence, and young adults, such as obesity, musculoskeletal pain, asthma, and allergy. The association between somatic diseases and ADHD in older adults is largely unknown. In Lensing et al's study of 149 adults aged >=50 years with ADHD, 46.6% reported co-occurring somatic disorders. Hypothyroidism 20.6%, hypertension 19.1%, fibromyalgia 16.2%, and arthritis 16.2% were the most common disorders. Another finding from the same sample showed that 73.7% of the patients reported moderate-to-severe pain/discomfort on EuroQoL, in comparison to 43.8% in the age- and sex-matched population norm. In a small sample of eleven clinically recruited patients with mean age 61.6 years, 55% had somatic disorders like hypertension, type 2 diabetes, and ischemic heart disease. In a study comparing 23 older adults with 208 controls without ADHD, the authors could not find significant differences in a number of somatic diseases, like chronic lung disease, cardiovascular disease, diabetes, arthritis, and cancer. In an adjusted regression analysis, they found, however, that the number of ADHD symptoms was associated with the presence of chronic lung disease, cardiovascular disease, and number of somatic diseases. Interestingly, the authors found no association between ADHD and an unhealthy lifestyle.
A number of controlled follow-up studies have shown that ADHD in young adults is associated with impairment in several life domains, such as academic, occupational, and social functioning. In a study of 148 adults aged >=50 years with ADHD (mean age 55.7 years), compared to an age group-matched reference sample, the ADHD patients were significantly more often single (41.5% versus 25.2%) and less frequently employed (48.8% versus 69.2%). Surprisingly, in this study the level of education was not different between groups. The study showed that adults aged >=50 years with ADHD reported significantly reduced quality of life compared to population norms. A Dutch study that recruited patients with a mean age 68 years also found a significantly higher level of divorced/never married in the ADHD group compared to the non-ADHD group (26.1% versus 10.1%). They also found that ADHD was associated with having fewer family members in their network and experiencing emotional loneliness. Because of the presence of only a few studies, relatively small samples, and different age groups, it is not possible to draw definitive conclusions about impairment in adults aged >=50 years with ADHD. However, the results indicate that the negative impact of ADHD seems to persist into late adulthood. In a paper based on a study of 24 clinically referred older adults with ADHD, Brod et al found that the quality of life suffers from the accumulated negative impact of ADHD symptoms and impairments on their professional, economic, social, and emotional well-being. At the same time, none of the patients in this study indicated worsening of ADHD symptoms with aging, and some stated that living with ADHD got easier with age. Similar findings are also described by the patients in the paper by Henry and Jones.