Is ADHD And Parkinson's Disease Linked?
Yes, there is a potential link between these two conditions arising mainly from epidemiological studies.
Recent studies suggest a potential link between attention-deficit/hyperactivity disorder (ADHD) and Parkinson's disease (PD). Epidemiological evidence indicates that ADHD diagnosis is associated with an increased risk for diseases of the basal ganglia and cerebellum, including PD, possibly due to deficits in striatal dopamine shared by both disorders [27]. However, the magnitude of the direct effect of ADHD on neurodegeneration is yet to be determined and the mechanism of how or why ADHD is associated with an increased risk of developing a neurocognitive disorder is still unclear [28].
What Is ADHD?
Attention Deficit Hyperactivity Disorder, more commonly known by its acronym ADHD, is a mental health condition.
ADHD is characterized by unusual levels of hyperactivity, impulsivity, and problems with attention [1]. It is considered a neurodevelopmental disorder and is usually first diagnosed in childhood and can continue into adulthood [2, 3] (although it can be diagnosed in adults as well [4]).
People affected by ADHD usually have problems focusing on a single task or sitting still for long periods. This can interfere with their daily life and may affect their studies, work, relationships, or even home life [1]. Some less known symptoms of ADHD include fatigue, problems with eye contact, aphantasia or even hypermobility.
Individuals affected by ADHD can also act more impulsively than others, ultimately making it harder for them to perform well in school or work [2].
The prevalence of ADHD is estimated by the American Psychiatric Association to be 2.5% of adults and 5.3% of children [5, 2, 6].
What Is Parkinson's Disease?
Parkinson’s disease (PD) is a neurodegenerative disorder affecting the motor system [7, 8, 9, 10, 11].
It is characterized by the progressive loss of dopaminergic neurons in the substantia nigra part of the brain [7, 8, 9, 10, 11].
The clinical manifestation of such progressive loss of dopaminergic neurons can be observed as slowness of movement or impaired movements. People affected by PD also have problems with balance, impaired posture, coordination of muscles, and we can observe resting tremor or rigidity [12, 8, 13, 14, 15, 16, 17, 9, 18, 11].
In addition to these motor symptoms, we can also observe neuropsychiatric manifestations of the disease such as depression, anxiety, and cognitive impairment. Some patients may even experience apathy, a lack of interest or enthusiasm, and sleep problems [12, 19, 13, 14, 15, 16, 9, 18].
The causes of Parkinson's are not entirely understood. Some research suggests that PD can be caused by head injuries, childhood stress, or even benzodiazepine use.
PD affects roughly 1% of the population over the age of 60 years [20].
What Are The Differences In Available Treatment For ADHD And Parkinson's Disease?
Interestingly, treatments for both ADHD and PD work on modifying dopamine levels in the brain, although the specific medications and therapeutic approaches differ significantly.
ADHD
The primary treatment for ADHD is stimulant medications. Examples of such may be amphetamine/dextroamphetamine (Adderall) or methylphenidate (Concerta, Ritalin) [21]. These drugs work on the principle of increasing dopamine levels in the brain, which helps stimulate focus and attention [21].
Other drugs, considered as non-stimulant drugs, and cognitive behavior therapy are also often recommended [21].
What are some non-stimulant drugs for ADHD
Non-stimulant drugs for ADHD include **viloxazine**, a selective norepinephrine reuptake inhibitor, and **atomoxetine**. Other options include **guanfacine** and **clonidine**, which are alpha-2 adrenergic receptor agonists. Antidepressants such as **bupropion** and **venlafaxine** may also be used. These drugs are often chosen when patients do not respond to or cannot tolerate stimulants, or when there's a risk of substance abuse [27], [28], [29], [30], [31], [32], [33], [34], [35], [36], [37].
On the other hand, the primary treatment for PD is dopamine replacement therapy, usually done using levodopa. This drug helps alleviate motor symptoms and improve the activities of daily living [22]. It works on the principle of dopamine agonist and thus works as a replacement for dopamine. Other drugs that can also serve as dopamine agonists are monoamine oxidase B inhibitors [23].
However, in advanced stages of PD, surgeries like deep brain stimulation or levodopa-carbidopa intestinal gel infusion are recommended [23].
Recent research suggests lixisenatide as a potential drug against Parkinson's.
What Is The Difference In Diagnosis ADHD And Parkinson's Disease?
Although ADHD and PD are two distinct conditions, they both affect the central nervous system. They share several neurochemical changes, although they have their own diagnostic criteria [21].
ADHD
ADHD is typically diagnosed based on a pattern of inattention and/or hyperactivity. Often, tools like ADHD Rating Scale-IV are used to determine whether an individual has such a condition [24, 25].
PD
PD is primarily diagnosed based on the presence of motor symptoms and MRI scans determining a brain volume change. In particular, the clinician is looking for symptoms like bradykinesia, rigidity, or tremors. Although cognitive symptoms may appear as well, they don’t make the primary basis for diagnosis [26].
Interestingly, patients with ADHD have a 2.4-fold increased risk of basal ganglia and cerebellum diseases, which include PD [17]. However, this does not mean that the presence of ADHD directly means that the individual will develop PD, but may suggest a potential link between these two diseases [17].