Attention Deficit Hyperactivity Disorder (ADHD) was described a long time ago, but its etiology remains unclear. It ranks as the most prevalent behavioral disorder in children that persists well into adulthood. Hyperactive or impulsive behavior and attention lapses are core symptoms used in diagnosis. This paper reviewed current knowledge about ADHD, including the diagnostic criteria, etiology, symptoms, and treatment. Overall, this disorder manifests clinically as persistent hyperactivity and inattention. Neuropsychological deficits in executive functions underpin these symptoms. Pharmacological treatments target prefrontal cortex networks to improve cognitive functioning and behavioral performance. Further research is suggested in the area of pharmacogenetic to develop effective drugs with minimal side effects on patients.
Neuropsychological disorders are related yet varied conditions in symptomatology, complications, and etiology, with many being congenital. They manifest as lasting symptoms, mainly impaired cognitive functioning, attention problems, and hyperactive episodes. Attention Deficit Hyperactivity Disorder (ADHD) is the most prevalent clinical form of attention disorder first identified over two centuries ago. Initially, it was categorized as a form of brain damage, and psychostimulants were administered to ameliorate impulsive symptoms and motor problems in children. Over the years, advances in neuropsychology contributed to the current understanding of ADHD, notably, its neurochemical basis. This paper reviews existing knowledge about the disorder, including its diagnosis, etiological mechanisms, symptoms, and pathophysiological development. The impact of ADHD on patients’ quality of life, treatments, and directions for future research are also suggested.
ADHD is a persistent childhood-onset syndrome that presents with disruptive behaviors of variable severity. Affected children may exhibit attention deficits, impulsivity, or hyperactivity (Mahone & Denckla, 2017). These atypical behaviors are often considered to have a psychosocial rather than neurological origin, hence, the disorder is mostly under-diagnosed. Understanding its diagnosis, etiology, symptoms, impact, and available interventions would lead to better outcomes for patients.
What is Known About ADHD: Diagnosis
Although ADHD was recognized several years ago, its diagnosis remained controversial until recently, when the neurochemical framework was adopted to explain behavioral manifestations of this disorder. A review by Mahone and Denckla (2017) noted that the current diagnostic criteria are a product of neuropsychological research, notably, the continuous performance tests conducted on children diagnosed with the hyperactive reaction of childhood (ARC) in the 1980s. These measures revealed that attention is related to the hyperactive syndrome and thus became the defining descriptor of the disorder. Consequently, DSM-III described ARC as an attention deficit disorder that was revised to its current name, ADHD, after hyperactivity was included in the diagnostic criteria (Mahone & Denckla, 2017). Therefore, combined inattentive and hyperactive behavior remain the key distinguishing descriptors of ADHD.
The age of onset is a critical factor in diagnosing this disorder. Currently, ADHD is clinically recognized as a neurodevelopmental syndrome diagnosed in childhood (Shaw & Polanczyk, 2017). These diagnostic changes are based on the neurochemical basis of behavior and cognitive disruptions. Under the DSM-V, onset age of 12 years, observed inattentive, hyperactive, or impulsive behavior, and at least five symptoms for adults are required for diagnosis (Shaw & Polanczyk, 2017). Further, these behaviors must be present for several months and in multiple environments. Overall, ADHD diagnosis in adults is more challenging than in children because it is complicated by comorbidities in adulthood (Mahone & Denckla, 2017). Additionally, childhood medical history may not be available for most people.
ADHD is the most prevalent attention disorder in childhood worldwide. Its etiology is unclear, but genetic, neuropsychological, and environmental factors play a role in its onset and progression. ADHD is a heritable disorder, with first-degree relatives of affected people being five-to-ten times more likely to develop the syndrome (Mahone & Denckla, 2017). It is polygenic and multiple genes are implicated in the different disease phenotypes and presentations. Gene variants conferring a higher risk influence brain development and neurotransmitter pathways and receptors (Mahone & Denckla, 2017). These genes are ideal targets for potential treatments that reduce symptom severity and have minimal adverse effects on patients.
Another significant etiology of ADHD in infancy or early childhood is brain injury, which has many underlying causes. Notably, alcohol and tobacco use during pregnancy are key risk factors for ADHD, suggesting that teratogens such as nicotine affect fetal brain development (Shaw & Polanczyk, 2017). Behavioral disturbances may also result from traumatic brain injury and exposure to toxins. Thus, adverse psychosocial environments affect early neurological processes, resulting in impaired cognition and disruptive behavior, such as inattention and impulsivity, which are associated with ADHD. Evidence from magnetic resonance imaging shows that ADHD is linked to poor functioning and structure of circuitry in the prefrontal cortex (PFC) (Shaw & Polanczyk, 2017). This part of the brain regulates attention and behavior and thus reduced PFC networks exacerbate ADHD symptoms in children.
Symptoms and Pathophysiology
Core ADHD symptoms usually start in early childhood and are chronic, impacting the social and educational outcomes of affected children. They include elevated inattention, hyperactivity, and impulsive behavior (Mahone & Denckla, 2017). ADHD is often associated with learning disabilities, depressive symptoms, and mood disorders in childhood. The syndrome is recognized as a developmental issue that impedes early neurological growth, delaying cognitive and socio-emotional skills. Over the past decade, ADHD has been associated with poor mental health outcomes and potential behavioral issues in patients (Agnew-Blais et al., 2018). Thus, cognitive deficits in ADHD typically manifest as secondary effects of behavioral dysfunction, problems with self-regulation, and poor psychological performance. In recent years, concerns have been raised over the development of behavioral disruptions in children with untreated ADHD, including delinquency, anxiety, and depression (Sibley et al., 2021). Thus, behavioral issues usually co-occur with mental health disorders in ADHD patients, complicating the social, physical, and emotional functioning of the affected individuals.
The chronic course and persistent effects of ADHD in adults are another area of concern. Agnew-Blais et al. (2018) explain that the long-term impact of ADHD in children persists into early adulthood and affects behavioral outcomes. They describe ADHD as a condition that typically co-occurs with multiple psychological disorders, manifesting as persistent cognitive dysfunction, anxiety, and behavioral issues, such as suicidal ideation and substance disorders, in adults. However, the symptoms of inattention, hyperactivity, and impulsive behavior are fewer in adulthood and thus a lower threshold is required for diagnosis. Guo et al. (2021) found significant cognitive impairments in most adults with ADHD, hence, a comprehensive assessment of key mental strengths and deficits is necessary to inform treatment plans. Measurement of variables such as processing speed, planning ability, and task switching would give an informative neuropsychological functioning profile of an adult with this disorder.
ADHD is characterized by multiple neurological deficits that manifest as the core clinical symptoms of this disorder. The cognitive difficulties develop from problems with reward processing in the default-mode network of the brain that results in slow responses, attention lapses, impaired memory, and inhibited self-regulation (Shaw & Polanczyk, 2017). The inhibition of the executive functions manifests as secondary symptoms of inattention and episodes of hyperactive or impulsive behavior. Additionally, the impairments result in psychomotor deficits, which impact domains such as learning, task processing, and performance.
Impact on Quality of Life
Based on the symptoms identified in this review, ADHD affects the psychological, social, and academic functioning of affected individuals. The quality of life (QoL) is primarily self-reported impaired performance due to a disease or treatment. It may be indicated by a decline in the capacity to do daily living activities and reduced socio-emotional, academic, or occupational functioning. People with symptomatic or poorly managed ADHD experience higher levels of anxiety, depressive symptoms, and daytime drowsiness than healthy individuals (Mahone & Denckla, 2017). The poor mental health outcomes contribute to lower subjective scores in QoL. Therefore, treatments targeting these symptoms would lead to better outcomes and ameliorate the effect of ADHD on QoL.
Various clinical aspects of ADHD contribute to the low satisfaction with life among patients. Social and emotional dysfunction predict feelings of being dissatisfied with one’s QoL among adults (Mahone & Denckla, 2017). These predictors are key targets for tailored treatments to improve the QoL of symptomatic individuals. Children with ADHD have lower social and academic achievement than their non-ADHD counterparts because of the neurodevelopmental effects of this disorder (Shaw & Polanczyk, 2017). They struggle with basic reading, numeracy, and verbal expression, as ADHD often co-occurs with other learning disabilities, such as dyslexia. Therefore, children with severe symptoms will have poor academic performance in preschool. Early identification and diagnosis are necessary to treat cognitive and educational impairments that may persist into adolescence and adulthood.
Subjects mainly suffer low QoL because ADHD typically co-occurs with psychological conditions. COVID-19-related restrictions are associated with changes in sleep quality and anxiety in children with ADHD, probably due to limited access to medical care during the pandemic (Sciberras et al., 2020). Further, behavioral disruptions and functional deficits may predispose these individuals to low self-esteem and poor social relationships. Further, the disorder is a lifelong syndrome, which means that it impacts the educational outcomes of students with ADHD. As a result, their employability is likely to be low, especially when this condition is not identified and treated in preschool. Among adults, inattention and impulsive behavior are associated with poor time management, procrastination, and a tendency to be easily distracted (Shaw & Polanczyk, 2017). These factors contribute to productivity loss and impact the QoL of people with ADHD.
Poor psychomotor control and behavioral symptoms such as impulsivity impact occupational outcomes, including performance and safety. Further, individuals with ADHD suffer social issues, which may include the inability to initiate and maintain relationships, low self-confidence, and disruptive behavior (Velõ et al., 2019). They find it difficult to navigate through the social environment because of impaired psychosocial functioning and poor self-regulation. As a result, adults may be predisposed to poor mental health outcomes, especially for undiagnosed cases that lack psychosocial support.
Besides ADHD symptoms, access to appropriate treatment impacts an individual’s quality of life by improving the behavioral and cognitive deficits. Non-stimulant medications, such as Atomoxetine, enhance perceived QoL of patients by ameliorating symptoms of ADHD, resulting in better self-regulation, self-esteem, and psychosocial functioning (Shaw & Polanczyk, 2017). Thus, proper diagnosis and treatment are critical to symptom improvement from the baseline, as indicated by better performance in interpersonal domains. Further, based on these findings, improved symptomatology is associated with higher QoL scores after receiving treatment.
Stimulant medications are also administered to improve primary symptoms of ADHD. Amphetamine salts are effective in reducing symptom severity in patients diagnosed with either hyperactivity or inattention (Velõ et al., 2019). As a result, individuals under treatment function better physically, emotionally, and socially, which, in turn, improve their mental health. Sleep quality is another outcome of medication that contributes to an increase in perceived QoL score. Most individuals with ADHD complain of difficulties falling asleep, wakefulness, and disturbances (Velõ et al., 2019). Treatment with psychostimulants enhances daytime functioning and nighttime sleep quality, contributing to an improvement in overall QoL.
Treatment of ADHD
ADHD has no standard treatment, but specific therapy options are recommended to relieve chronic symptoms. For children, these measures include medication, non-medication approach (psychosocial treatment, behavioral training, or education), or a combination of both (Velõ et al., 2019). The two treatment modalities are often used together to achieve optimal outcomes for the patient. Research evidence supports the utilization of combined strategies, especially for individuals with severe symptoms of ADHD. In a study that involved 579 affected children aged 7-9 years, medication and combination therapy were found to produce the most significant improvement in symptoms compared to psychosocial support (Mahone & Denckla, 2017). Thus, a long-term use of both pharmacological and non-pharmacological strategies may help alleviate severe impulsivity, hyperactivity, and inattention associated with this disorder, allowing the child to attain age-appropriate developmental, social, and academic milestones.
Overall, three non-pharmacological treatments are indicated for ADHD symptoms in childhood, with significant involvement of family members. The first one is parental behavior training, where a primary caregiver is taught better methods to help his or her child (Velõ et al., 2019). It entails regular sessions that promote healthy parent-child relationships and build skills for preventing behavioral disruptions as soon as they develop. Family members are also taught techniques for optimal organization of tasks so that the child can handle them easily. Parents also learn to establish an effective reward system to motivate and sustain positive behavior in children.
The second approach is psychosocial therapy offered by a professional. Behavioral training combined with motivational interviewing improves social skills and behavioral and emotional control when delivered by a competent therapist in community settings (Fallah & Ortiz, 2021). The third method includes school-based programs, including special education, which help children with ADHD overcome academic deficits by providing an optimal learning environment and activities. ADHD co-occurs with learning disabilities, which usually manifest as reading and numeracy difficulties (Mahone & Denckla, 2017). Educational interventions are designed to assist the child to succeed in these functional and academic domains.
Pharmacological treatments, either alone or in combination with psychosocial therapy, are commonly used to ameliorate ADHD symptoms. They include stimulants and non-stimulant medications that produce a calming effect on hyperactive behavior (Velõ et al., 2019). An important consideration when using pharmacological strategies includes the side effects of the drugs. Most children benefit from the psychostimulants prescribed for the hyperactivity or inattention subtypes of the disorder. These medications enhance neurotransmitter activity, which helps improve ADHD symptoms, usually for a short time (Mahone & Denckla, 2017). Thus, psychostimulants may be short-acting or long-acting and are administered orally or via transdermal patches.
Commonly used stimulants offer symptom relief when taken in the correct dosage. Children may be given amphetamines or methylphenidates, which have been approved for children aged six and above (Velõ et al., 2019). The main concerns with stimulant drugs include heart problems, such as elevated heart rate, hypertension, and psychotic or manic episodes after prolonged use. Thus, these side effects must be monitored so that the medications are discontinued if the disruptive behavior worsens. Non-stimulant medications are also indicated as better options where stimulants produce adverse effects. They include Atomoxetine that elevates norepinephrine concentrations in the brain and Guanfacine that targets PFC to improve attention and impulse control (Mahone & Denckla, 2017). However, non-stimulants act much more slowly than stimulants and may not cause immediate symptom relief.
Pharmacological treatments have been compared with non-pharmacological interventions to determine the most effective strategy for ameliorating ADHD symptoms. A review by Mahone and Denckla (2017) found that methylphenidate titration thrice a day combined with intensive psychotherapy is standard care for ADHD. Further, a medication-alone strategy is less effective than non-pharmacological interventions in ameliorating symptoms when comorbidities are absent. The superiority of behavioral therapy is due to the adverse effects of medications in children. Besides behavioral treatments, diet and cognitive training have been used to improve ADHD symptoms with variable levels of efficacy. Overall, the effectiveness of pharmacological or non-pharmacological interventions depends on a careful assessment to detect and treat comorbidities that affect treatment outcomes.
Currently, ADHD stands as one of the most under-diagnosed and undertreated psychological disorders worldwide. In my view, the chronic course of ADHD symptoms and lifelong effects that do not diminish even in adulthood will require family-based interventions where practitioners work with a person with this disorder across his or her lifespan. The studies assessed have shown that combination therapy (medication plus behavioral training) may alleviate cognitive and behavioral impairments when delivered for a prolonged period, such as several months or even years (Velõ et al., 2019). Future research should examine the long-term outcomes of family-based intervention provided throughout a person’s life. Access to social supports within the family or community should ameliorate ADHD symptoms when used with other interventions.
Stimulant drugs are associated with adverse outcomes on patients and alternative medications (non-stimulants) take a long period to reach a full effect. Further research should focus on developing non-stimulants agents with high efficacy, but fewer adverse effects. Most existing non-stimulant drugs, such as Atomoxetine and Guanfacine, have been developed for pediatric populations (aged above six years), which makes them less effective in adults and preschoolers. Future medications should be tested in multiple cohorts so that they can be prescribed for all patients, regardless of age or gender.
In conclusion, many questions remain about ADHD etiology that need further investigation. The identification of putative variants influencing the expression of neurotransmitters and their receptors will lead to medicines tailored for each ADHD subtype that has been characterized. ADHD has also been hypothesized as a polygenic condition that involves additive gene effects. With the recent advances in human genome sequencing, further research should aim to identify all genes associated with increased ADHD risk. This approach will improve our understanding of the genetic etiology of this disorder. Additionally, the effect of gene-environment interactions on symptom severity requires further investigations to identify psychosocial support systems associated with better outcomes.
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