The prevalence of attention-deficit/hyperactivity (ADHD) in adults has not been investigated systematically, but estimates based on a prevalence of ADHD in children of 5% to 10%, and an estimated persistence rate of 50% to 60% into adulthood, suggest that ADHD may afflict as many as 2% to 4% of the population. 
The clinical interview remains the bedrock of the adult ADHD diagnosis to asses the three core features of the disorder in adults accurately: symptoms dating back to early childhood, significant impairment in at least two settings (e.g. work and home), and moderate or severe ratings for at least six of nine symptoms of inattention or hyperactivity. 
Childhood ADHD was first recognized in the early 1900s, but recognition of the disorder’s persistence into adulthood did not occur until the 1970s.
An encephalitis lethargic pandemic that occurred in the late 1910s and early 1920s provided the first clues to ADHD symptomatology, because those who survived experienced residual symptoms quite similar to those of ADHD (hyperactivity, lack of coordination, learning disability, impulsivity, and aggression): the lasting effect of the virus on the behaviour of survivors marked the first instance in which states of pathologic restlessness were attributed to neuropathology deficits rather than psychological causes. In addition, survivors suffered damage to the dopamine-rich substantia nigra, a brain region that is thought to affect ADHD symptomatology.
The Second Edition of the Diagnostic and Statistical Manual (DSM-II) described the hyperkinetic syndrome, emphasizing the motoric over-activity.
In 1980, the Third Edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM-III) emphasized for the first time inattention (with and without hyperactivity) and designated an attention-deficit disorder (ADD) classification. DSM-III briefly mentioned that it was possible for ADHD to persist into adolescence or adulthood, but it provided no description of adult symptoms.
The Revised Third Edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM-III-R)  stated that ‘‘approximately one-third of children with ADHD continue to show some signs of the disorder into adulthood”: it was the first edition that fully recognized the possibility of ADHD in adults. Adults who showed signs of ADHD were considered to have the disorder, but they had to have experienced those symptoms since early childhood. Other changes in the revised third edition included changing the name of the disorder to attention deficit/hyperactivity disorder from attention-deficit disorder.
The Forth Edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV) was the first to acknowledge that full-fledged ADHD can persist into adulthood, but in order to have the diagnosis, ADHD must begin in childhood, and evidence of the condition must be shown by age 7. Another change in the fourth edition was placing impulsive and hyperactive symptoms in the same list but keeping them separately identified.
The Text Revision of the Fourth Edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV-TR) outlines three major criteria for making the ADHD diagnosis:
- moderate severity ratings for at least six of nine symptoms of inattention or hyperactivity,
- impairment in at least two settings (such as work or school and home)
- symptoms dating back to early childhood.
Comorbidity is very common with ADHD patients, with estimates as high as 80% [4,5,]. The mood disorders, including major depression, bipolar disorder, and dysthymia, have a comorbidity rate with ADHD ranging from 19% to 37%. Dysthymia, in particular, is quite common for adults with ADHD: in some cases it may be a result of living for years with undiagnosed, untreated ADHD. In other cases, the dysthymia may be co-occurring but not connected, a correct diagnosis in this case can be very difficult.
The comorbidity rate for anxiety disorders ranges from 25% to 50%. The range for alcohol abuse is 32% to 53%, and for other types of substance abuse, including marijuana and cocaine abuse, the comorbidity rate is 8% to 32%.
The rate of comorbidity with personality disorders is 10% to 20%, and for antisocial behaviour, the rate of comorbidity is 18% to 28% [5,6–10].
For learning disabilities, particularly auditory processing problems like dyslexia and auditory processing deficits, comorbidity is 20% .
There are several key steps to diagnosing a patient, including discussion of current symptoms, childhood history and comorbidities.
Clinicians should query patients about particular aspects of their adult experience, including current functioning/presenting symptoms, family history, academic/vocational indicators, marital functioning, and physical signs. As a start, rating scales, such as the ADHD Rating Scale (ADHDRS) or the Conners Adult Attention-Deficit Rating Scale (CAARS), can be used to assess current symptoms.
Collecting some data on childhood history from a parent or older sibling, if possible, is extremely helpful. Formal records such as report cards and conduct reports are also illuminating. To assess comorbidity, one can conduct a semi-structured interview or use an assessment tool.
Barkley and other authors believe that many of the problems that adults with ADHD experience originate from poor control over executive functioning, linked to deficits in the frontal regions of the brain: when problems arise in one or more of the three areas of behavioural inhibition (inhibiting an initial response to an event, stopping a response once it has started, and protecting a response from interference and distracters), executive functioning difficulties may occur This description helps conceptualize how symptoms of both inattention and hyperactivity/impulsivity could arise from similar deficits.
Adult patients whose underlying difficulties are ADHD symptoms will often present mood symptoms; they may also have a child who has ADHD, or they could present problems at work or home.
Frequent global problems include inability to concentrate, lack of organization, inability to establish and maintain a routine, poor discipline, depression or low self-esteem, forgetfulness or poor memory, and confusion or trouble thinking clearly . Other problems include procrastination, lack of motivation, and mood liability can also occur . Common characteristics for adults with ADHD can include stubbornness, chronic conflicts with authority, difficulty in spouse and peer relationships, frequent job changes, poor frustration tolerance, and poor academic performance despite average or even above-average intelligence .
When depressive ideation is present, a distinction needs to be made between depressive symptoms resulting from living with undiagnosed ADHD and a comorbid (or primary) diagnosis of depression.
Wender believes that if the ADHD is the primary diagnosis, then it is more likely that the depression is secondary to mood liability. The mood liability seen in ADHD, however, can be difficult to distinguish from persistent and more pervasive mood changes in bipolar disorder; the longitudinal differential diagnosis with bipolar disorder is complicated further by the fact that Wozniak et. al.  have established that nearly all patients with childhood onset bipolar disorder also have ADHD. Wender et. al. believes that mood dysregulation is central to ADHD, whilst other researchers consider the high rates of mood symptoms to be caused by comorbid conditions.
Occupational and educational challenges
Adult symptoms can be quite similar to those experienced in childhood. Adults are not just grown-up children, however, and their symptoms reflect the changes in their activities and responsibilities. Some adults may not have been diagnosed as children, because the firm structure and relatively minimal demands of childhood meant their symptoms did not create noticeable problems, but later the demands of adulthood and the struggles that ensued made their symptoms overt and treatment necessary.
When a person’s roles and responsibilities change upon entering adulthood, symptom manifestation can also change, particularly the symptoms associated with hyperactivity and impulsivity. Hyperactive and impulsive symptoms decrease more rapidly with age, in comparison to symptoms of inattention. 
For example, aimless restlessness in childhood can turn into purposeful restlessness in adulthood, childhood hyperactive symptoms (like difficulty remaining seated, running and climbing excessively, squirming and fidgeting, difficulty playing quietly, and talking excessively) commonly are manifested in adults with adaptive behaviours like working two jobs, working long hours, or choosing a very active job.
For most of patients problems related to executive functioning persist in work: patients frequently present with occupational problems like difficulty finding and keeping jobs, job performance below level of competence, and inability to perform up to intellectual level in school . Many patients with ADHD will present complaining of problems at work, whether they are related to completing tasks or interacting with co-workers.
The Milwaukee Young Adult Study found that employees with ADHD are more likely to be fired, display more ADHD/oppositional–defiant disorder (ODD) symptoms on the job. Some of these symptoms resemble those of antisocial personality disorder (ASPD), however an ASPD patient’s difficulties are more often premeditated and damaging: ADHD patients instead, have no desire to violate societal norms.
Many adults with ADHD do not regulate themselves well and do not self-correct when problems arise, in part because of poor self-monitoring . Poor time management and difficulty completing and changing tasks are common manifestations of inattention.
Adults with ADHD experience significantly more grade retention, and more students with ADHD are suspended or expelled. The dropout rate is also higher, and, on average, students with ADHD in the Milwaukee Young Adult Study also had lower class rankings and lower grade point averages, their educational or vocational performance was below what one would expect based on a patient’s intelligence and education.
Relationships and family life
The constant activity of an adult with ADHD can lead to family tensions ; more than 50% of adults with ADHD will have a child who has the diagnosis, which creates additional challenges . Problems for an ADHD family can include difficulties around organization, setting and keeping routines, day-to-day supervision, stress tolerance, mood stability, and compliance with ADHD treatment plans .
Many patients who are in romantic relationships may have been to marital therapy or may be experiencing relationship strife. Common issues would be not listening/interrupting when the spouse is speaking or a disorganized or inattentive approach to household responsibilities .
Gender and cultural consideration
As children, girls with ADHD have similar rates of mood, anxiety, and learning disorders as boys. Girls, however, have lower rates of conduct and oppositional disorder than boys: this is a reason why girls with ADHD could have been under-identified. In epidemiological and adult samples, the ratio is close to 2:1.
Rates of ADHD prevalence are similar across cultures . Cultural differences, however, can play a major factor in whether ADHD symptoms are seen by individuals as problematic, and, if they are, whether a person seeks care and stays compliant. Cultural differences in terms of expectations at home, in school, and in the community affect whether people seek treatment, as do attitudes and beliefs about illness, choice of care, access to care, degree of trust towards institutions and authority figures, religious beliefs, and tolerance for certain behaviours .
Adults with the disorder have dealt with their symptoms for years, and most have developed compensatory strategies to minimise the impact of symptoms. This affects diagnosis in a few ways: for example, elaborate coping strategies make impairment seem less severe than it is. When rating symptom severity, clinicians must account for the degree of compensation. Sometimes individuals chose jobs below their potential, or chose a spouse who provides organisational assistance to compensate for these difficulties.
Rating scales are useful for assessing whether a patient meets the DSM-IV diagnostic criteria necessary for an adult ADHD diagnosis. Rating scales also can be useful in assessing current symptoms. In terms of diagnosis and severity, the use of the 18 core DSM-IV symptoms has been established as valid and reliable.
There are several diagnostic systems and rating scales that assess domains outside of the traditional DSM-IV core symptoms. Although they may provide useful clinical information, until further investigation, the relationship of these additional domains to ADHD itself remains unclear. For instance, while functional impairments, such as social and occupational deficits, are important features of ADHD, they are not specific only to ADHD and are frequently present in individuals without ADHD who have other disorders.
The Conners Adult ADHD Diagnostic Interview for DSM-IV is a clinician-administered interview that assesses the presence of the 18 DSM-IV defined symptoms for childhood and adulthood. A diagnosis of ADHD, including subtype, then can be established.
Barkley’s Current Symptoms Scale-Self-Report Form is a self-report scale of 18 symptom items that correspond to the symptoms listed in the DSM-IV diagnostic criteria. Barkley also developed a Childhood Symptoms Scale-Self-Report Form, Developmental Employment, Health, and Social History Form, and Work Performance Rating Scale-Self-Report Form, all of which can be sent to patients to complete before their first clinic visit. In addition, the Current Symptoms Scale-Other Report Form provides observer ratings.
The Brown ADD Scales Diagnostic Form is clinician-administered. The clinician asks the patient about the clinical history of his or her family and about the patient’s physical health, substance use, and sleep habits. The clinician also obtains collateral data from an observer/significant other and screens for the full array of comorbid disorders.
Current symptom surveys
Current symptom surveys can be divided into clinician-administered and self-report forms. Some scales are normed and can provide population comparisons. Because symptoms like internalized restlessness, feeling disorganized, and easily getting distracted are not always apparent to observers, self-report scales are an effective way to capture the symptoms of adults with the disorder .
The ADHD-RS is an 18-item rating scale based on the DSM-IV criteria for ADHD, The ADHD-RS has been developed and standardized as a clinician-administered rating scale for children, but it can be used as an adult scale if the clinician has been trained.
The Brown ADD Scale is a frequency scale with 40 items. This assessment has normed, standardised, validated clinician-rated, and self-report forms.
The Wender-Reimherr Adult Attention Deficit Disorder Scale (WRAADS) is intended to measure the severity of the target symptoms of adults with ADHD using the Utah Criteria and was developed by Wender and Reimherr. The WRAADS may be particularly useful if the clinician wishes to assess possible mood liability symptoms of ADHD.
The full Adult ADHD Self-Report Scale (ASRS) Symptom Checklist-v1.1 is an 18-item scale that can be used as an initial symptom assessment to identify adults who might have ADHD. The scale queries patients about the 18 symptom domains identified by DSM-IV, with modifications to assess the adult presentation of ADHD symptoms. Neither the six-item screening version, nor the full 18-item symptom assessment version, is meant to be a stand-alone diagnostic tool.
From “Diagnosis and evaluation of adults with attention-deficit/hyperactivity disorder”;
Psychiatr Clin N Am 27 (2004) 187–201
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