It also removes the frustrating "and/or" element of our current ADHD diagnostic label (i.e., attention-deficit [and/or] hyperactivity disorder), which has watered down the diagnosis to something largely unfalsifiable IMO. The emphasis on hyperkinesis also fits with the neurobiological models of the disorder that implicate frontostriatal circuitry (which is admittedly a literature I take with a large grain of salt).
Given its origins as "hyperkinesis" and the subcortical link I mentioned above, I've posed questions to pediatric colleagues about whether they think of (hyperactive-impulsive) ADHD as a movement disorder. All have said that they do not.
I have to say, I really struggle with the concept of lumping ADHD (I am assuming strict reference to the predominately hyperactive subtype, based on description) into the category of movement disorders. You alluded to some overlap in dopaminergic dysfunction and basal ganglia involvement between ADHD and movement disorders,
but the clinical and pathological features remain distinct. You referenced Parkinson's and Huntington's disease correlates and referenced dopaminergic processes implicit in those, but I feel like the comparison is a bit lacking in neuropathophysiological distinctions that make each condition so unique.
For a simple example, if it was truly all treated "dopaminergically" as you alluded to, why not treat PD and HD with stimulant medications, which is not considered routine or best practice approach? In fact, VMAT2 inhibitors are actually the only recommended treatment for the choreatic movements in HD, which is interesting in that these are also what are sometimes recommended in tic/Tourette's treatment too... which I feel is much more representative of a movement disorder than ADHD. Conversely, why not treat ADHD with Sinemet? It also does not speak to why alpha-2-adrenergic agonists and an SNRI like Strattera that blocks NET, has demonstrated efficacy in treating the hyperactivity (hyperkinetic?) symptoms.
While I am not personally, the biggest proponent of a2a agonists, I have to recognize that they act by stimulating presynaptic alpha-2 receptors, thereby inhibiting the release of
norepinephrine. This results in decreased neuronal firing in the locus coeruleus and enhanced prefrontal cortical function, which is associated with better regulation of attention, impulse control, and activity level. I have preference for Strattera, which
treats hyperactivity in ADHD by selectively inhibiting the presynaptic norepinephrine transporter, increasing norepinephrine levels in the PFC, which improves behavioral control and reduces hyperactive/impulsive symptoms. Regardless, it's more PFC vs. basal ganglia.
For more on the specifics about how they differ, Movement disorders such as Parkinson's and Huntington's are defined by involuntary motor abnormalities, tremor, rigidity, bradykinesia, chorea, dystonia,
arising from specific neurodegenerative changes in motor control circuits, particularly the basal ganglia and related pathways. Parkinson's disease, for example, is characterized by progressive loss of dopaminergic neurons in the substantia nigra and the presence of Lewy bodies, leading to hallmark motor symptoms and pathologically confirmed neurodegeneration. Huntington's disease is marked by involuntary choreic movements and cognitive decline, with selective neuronal loss in the caudate and putamen.
While ADHD does involve increased voluntary activity (hyperactivity), these movements are purposeful and not due to abnormal motor system function. Neuroimaging and neurobiological studies show that ADHD is associated with delayed cortical maturation and dysfunction in frontostriatal and mesolimbic circuits, but not with the neurodegenerative changes or involuntary motor phenomena seen in movement disorders .
Although there is some overlap in dopaminergic dysfunction and basal ganglia involvement between ADHD and movement disorders, the clinical and pathological features remain distinct. ADHD does not present with the involuntary, progressive motor symptoms or structural brain changes (e.g., substantia nigra degeneration) that define Parkinson's or Huntington's disease. Motor control difficulties in ADHD are subtle, often related to executive dysfunction and response inhibition, and do not meet criteria for movement disorder diagnosis.
Happy to discuss further and can certainly produce cited literature (excluded from here because this is already a long post lol) if you would like.
