January 10, 2022
ADHD is hypothesized to arise from 1) poor inhibitory control resulting from impaired executive functions which are associated with reduced activation in the dorsolateral prefrontal cortex and increased activation of some subcortical regions; and 2)hyperarousal to environmental stimuli, hampering the ability of the executive functioning system, particularly the medial frontal cortex, orbital and ventromedial prefrontal areas, and subcortical regions such as the caudate nucleus, amygdala, nucleus accumbens, and thalamus, to control the respective stimuli.
These brain anomalies, rendered visible through magnetic resonance imaging, have led researchers to try new means of treatment to directly address the deficits. Transcranial direct current stimulation (tDCS) is a non-invasive brain stimulation technique that uses a weak electrical current to stimulate specific regions of the brain.
Efficacy:
A team of researchers from Europe and ran performed a systematic search of the literature and identified fourteen studies exploring the safety and efficacy of tDCS. Three of these studies examined the effects on ADHD symptoms. They found a large effect size for the inattention subscale and a medium effect size for the hyperactivity/impulsivity. Yet, as the authors cautioned, "a definite conclusion concerning the clinical efficacy of tDCS based on the results of these three studies is not possible."
The remaining studies investigated the effects on specific neuropsychological and cognitive deficits in ADHD:
The fact that heterogeneity in the methodology of these studies made meta-analysis impossible means these results, while promising, cannot be seen as in any way definitive.
Safety:
Ten studies examined childhood ADHD. Three found no adverse effects either during or after tDCS. One study reported a feeling of "shock" in a few patients during tDCS. Several more reported skin tingling and itching during tDCS. Several also reported mild headaches.
The four studies of adults with ADHD reported no major adverse events. One study reported a single incident of acute mood change, sadness, diminished motivation, and tension five hours after stimulation. Another reported mild instances of skin tingling and burning sensations.
To address side effects such as tingling and itching, the authors suggested reducing the intensity of the electrical current and increasing the duration. They also suggested placing electrodes at least 6 cm apart to reduce current shunting through the ski. For children, they recommended the use of smaller electrodes for better focus in smaller brains.
The authors concluded, "The findings of this systematic review suggest at least a partial improvement of symptoms and cognitive deficits in ADHD by tDCS. They further suggest that stimulation parameters such as polarity and site are relevant to the efficacy of tDCS in ADHD. Compared to cathodal stimulation, Anodal tDCS seems to have a superior effect on both the clinical symptoms and cognitive deficits. However, the routine clinical application of this method as an efficient therapeutic intervention cannot yet be recommended based on these studies ..."
Mohammad AliSalehinejad, Vahid Nejati, Mohsen Mosayebi-Samani, Ali Mohammadi, MilesWischnewski, Min-Fang Kuo, AllesioAvenanti, Carmelo M. Vicario & Michael A.Nitsche, "Transcranial Direct Current Stimulation in ADHD: A Systematic Reviewof Efficacy, Safety, and Protocol-induced Electrical Field Modeling Results," NeuroscienceBulletin(2020),https://doi.org/10.1007/s12264-020-00501-x.
Precocious puberty (PP) is defined as the onset of secondary sex characteristics before age 8 in girls or age 9 in boys.
Because it accelerates skeletal maturation by prematurely shutting down the cartilage growth plate at the tip of long bones, it tends to lead to shorter height in adulthood. It is also known to place an additional psychological burden on children, especially girls. Girls are four to 38 times more likely to develop PP than boys.
Taiwan has a single-payer national health insurance system, called National Health Insurance, that encompasses 99.6% of the island’s population. The Ministry of Health and Welfare uses it to maintain the National Health Insurance Research Database (NHIRD), enabling researchers to conduct nationwide population studies.
Using this database, a Taiwanese study team investigated the relationship between ADHD and precocious puberty among children and adolescents (under 18). And because methylphenidate (MPH) is the only psychostimulant approved for the treatment of ADHD in Taiwan, the team also explored the effect of MPH on this relationship.
Most diagnoses of ADHD in the NHIRD are made by board-certified psychiatrists, enhancing diagnostic validity.
Of the more than 3.3 million persons born in Taiwan between 1997 and 2001, 186,681 were diagnosed with ADHD. Of these, 122,302 were prescribed MPH.
After adjusting for sex, low-income households, and neuropsychiatric comorbidities, children diagnosed with ADHD were twice as likely to be diagnosed with PP. This held equally true for boys and girls.
However, children diagnosed with ADHD and prescribed MPH were more than a third less likely to subsequently be diagnosed with PP than those diagnosed with ADHD but not prescribed MPH.
For girls with ADHD, who without an MPH prescription were nine times more likely than boys with ADHD to be diagnosed with PP, an MPH prescription reduced that ratio to five times more likely than boys with ADHD and prescribed MPH.
That suggests a strong protective effect of MPH.
The team concluded, “Our study found that children with ADHD were at a greater risk of PP, and girls with ADHD were a particularly vulnerable group. … MPH appeared to be protective against PP in patients with ADHD, especially in girls. However, these preliminary results need further validation.”
Maternal infections and inflammatory responses during pregnancy have been proposed as risk factors for neurodevelopmental disorders such as ADHD.
Taiwan has a single-payer health insurance system that covers virtually the entirety of its population. Its Ministry of Health and Welfare maintains the National Health Insurance Research Database (NHIRD), with detailed information on outpatient services, hospitalizations, and medical treatment for nearly 99% of all residents.
A Taiwanese study team used NHIRD to examine to examine the relationship between maternal hospitalization for infection, and early childhood infection, and subsequent ADHD in offspring. The study cohort originated with all 3,260,879 individuals born between 2001 and 2018.
The team excluded births from foreign mothers, still births, births with congenital defects, low birth weights, abnormally late births, twins, triplets, and other multiple births, culminating in a final population cohort of 2,885,662 live-born single infants across 1,893,171 families, and 1,864,660 individuals with full siblings from 872,169 families comprising the full sibling cohort.
Study participants were followed until diagnosis of a neurodevelopmental disorder, their death, or the end of 2021.
After adjusting for sex, birth year, paternal and maternal ages, birthweight, birth season, parity, delivery method, 1 minute APGAR score (evaluating baby’s appearance, pulse, grimace, activity and respiration at birth), gestational age, pregnancy and delivery complications, parental history of neurodevelopmental disorders, maternal asthma and diabetes, urbanization level of the residential area, and family’s insurance amount, offspring of mothers hospitalized for infections had 14% greater odds of being subsequently diagnosed with ADHD.
However, in the full sibling cohort of over 1.8 million, this association vanished. That held true for each of the three trimesters of pregnancy. It also held true for bacterial infections. Surprisingly, offspring of mothers hospitalized for viral infections were 24% less likely to be diagnosed with ADHD than their siblings not exposed to maternal viral infection. Because of that, they also had a 6% lower risk overall.
After the same adjustments, early childhood infection was associated with 16% greater odds of being diagnosed with ADHD.
Nevertheless, in the full sibling cohort of over 1.8 million, this association again vanished. That held true overall, as well as separately for childhood infections in months 1-6 and months 7-12. The association vanished altogether both for bacterial infections as well as for viral infections.
The authors concluded, “the results of this nationwide birth cohort study with population and sibling analyses suggest that the association between maternal infection during pregnancy and offspring neurodevelopmental risk is largely due to familial confounding factors.”
Most previous studies of suicide and self-harm risk among persons with ADHD have focused on adolescents and adults. They’ve also tended to be cross-sectional, analyzing data from a population at a specific point in time.
An Australian study team took a different approach, conducting a before-and-after study through the birth cohort of the Longitudinal Study of Australian Children (LSAC), comprising 5,107 children who have been followed up every two years since birth.
The diagnosis of ADHD was based on parents reporting that their child had received a diagnosis of ADHD at or before age ten.
Suicide and self-harm were defined as children’s self-report at age 14 of any thought or attempt of suicide and self-harm respectively over the past year.
The team adjusted for the following confounders: socioeconomic status, birth weight, ADHD medication history, maternal education level, maternal age at birth, experience in bullying victimization at age 12, and depression score based on Short Mood and Feelings Questionnaire (SMFQ).
Of the 5,107 participants, 3,696 had all the valid data required for analysis and were included in the final cohort. Of these, 3.6% were diagnosed with ADHD by age 10.
With diagnosis of ADHD at age 10 and all other factors held constant:
Both depression and exposure to bullying were statistically significant mediators for the relationship. Nevertheless, depression and exposure to bullying each accounted for well under 10% of the overall effect.
Neither socioeconomic status nor maternal factors had any significant mediating effect on outcomes.
Conclusion:
The authors concluded, “This study provides compelling evidence that children diagnosed with ADHD at the age of 10 years face significantly elevated risks of experiencing suicidal thoughts, planning, or attempts, as well as self-harm, by the age of 14 years, which underscores the critical importance of recognizing and addressing these heightened risks in children with ADHD.”
While factors like depression and bullying contribute, ADHD itself remains a key risk factor. Early intervention and strong mental health support are crucial to protecting these children’s well-being.
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