This study set out to determine the prevalence and associated factors of attention deficit hyperactivity disorder among children attending the pediatric neurology and psychiatry clinics at Mulago National Referral Hospital.
The prevalence of ADHD
The prevalence of ADHD in our sample was 11.7% which is higher than the prevalence reported in prior African samples. A prior study found the prevalence of ADHD to be 6% among school children ages 7–9 years, from ten randomly selected schools in Kinshasa, Congo [
15]. Adewuya et al. found a prevalence of 8.7% among primary school children ages 7–12 years in Nigeria [
9]. The prevalence of ADHD in the clinic sample was higher than the prevalence found in the previously reported school samples. This difference is likely attributable to the different types of sample settings, i.e. a school versus a clinic. Children attending the neurology and psychiatry clinics from this sample are typically referred from other hospitals for specialized care and are often referred because an underlying neurologic or psychiatric condition is already suspected. The prevalence in this sample might not be a true reflection of the overall burden of illness in the country. Of note, some studies have indicated that culture and geographical location may have little or no influence on the prevalence of ADHD [
1,
9]. While the prevalence of ADHD in Africa was previously reported between 5.4 and 8.7% [
8,
9,
16,
17] in school going children samples, and 1.5% among the general community [
18]. Our finding of the prevalence of ADHD at 11.7% in a clinic sample is higher probably because the study participants in this study were obtained from a clinical setting; which is a highly specialized population. Other experts have argued that the variability of ADHD/HD prevalence estimates may be best explained by the use of different case definitions and that no variability of the actual prevalence across geographical sites should be found when case definitions are the same [
19‐
21].
Factors associated with ADHD
In this study, the male participants were three times more likely to have ADHD than the female participants. In this study the prevalence of ADHD was 8.4% in males and 3.3% in female participants aged 4–18 years. However, the observation in this study has been previously reported in other studies. Peter Szatmari et al. [
22] reported a prevalence of 9% among boys and that of 3.3% among girls, in an Ontario child health survey. Steven P Cuffe in a national health survey of a household population in the United Stated of America observed a prevalence of 6.8% among males and that of 2.5% among female children [
23]. Although this study did not categorize the subtypes of the ADHD among the study participants, this observation of a higher prevalence of ADHD in male children can be explained by the fact that female children have the inattentive type of the ADHD; as observed by Biederman et al. [
24]. Although, our study did not investigate any specific etiological factors associated with ADHD, these findings suggest that this may be worthwhile for future research to explore the possible mechanisms.
This study also observed that age less than 10 years was significantly associated with ADHD. Children less than 10 years were four times more likely to have ADHD. This observation might be attributed to having more children below 10 years (56%) attending the neurology and psychiatry clinics. Reported studies on ADHD among children have been done on different age groups. Biederman et al observed a decline in ADHD symptoms with increasing age among different age groups of children with ADHD over a period of 4 years [
25]. This possibly explains why more children with age less than 10 years had symptoms for ADHD compared to those with age of more than 10 years.
This study also found that abnormal vaginal discharge during first trimester of maternal pregnancy was significantly associated with ADHD. This finding could be explained by a possibility of the fetus being exposed to perinatal infections like TORCHES (Toxoplasmosis, Rubella, and Cytomegalovirus, Herpes simplex, Human immunodeficiency virus and syphilis). In this study, systematic screening for these maternal viral infections in the first trimester of pregnancy was not done. Mann Joshua et al. observed that school aged children born to mothers with a history of genitourinary infections were more likely to have ADHD. The study also observed that these mothers reported symptoms of abnormal vaginal discharge and urinary tract infections during their pregnancies [
26]. This could possibly explain the relationship between abnormal vaginal discharge and ADHD in this study.
This study found that a child whose primary caretaker had either no education or had primary education as their highest level of education was significantly associated with ADHD. This could be explained by the possibility that the caretaker of this child may have had undiagnosed ADHD in childhood which negatively impacted on their educational attainment. Biederman et al. in an overview of ADHD noted that 5–66% of children with ADHD persist with the disorder to adulthood and that parents of children with ADHD were likely to have ADHD [
3]. Sixty-four percent of the study participant had mothers as their primary caretakers. It is possible that some of these mothers had undiagnosed ADHD which persisted into adulthood.
This study also found that epilepsy was significantly protective against ADHD. This is a surprising finding because scientifically, epilepsy is thought to possibly increase the likelihood of having ADHD. Koneski et al. [
27] in a review article identifies possible common pathophysiological mechanisms between epilepsy and ADHD, which may help further understand the high prevalence of ADHD among epilepsy patients. The finding of epilepsy being protective against ADHD in this study could be explained by having epilepsy as the most common condition among study participants (71%) and yet a smaller proportion of the participants had ADHD (11.7%) compared to the bigger proportion of the participants (88.3%) who did not have ADHD. It might also be due to the fact that some of the AEDs, such as phenobarbital and benzodiazepines might have a negative effect on attention. The co-morbid conditions observed among participants with ADHD in this study were; epilepsy, autism spectrum of disorders, conducts disorders and intellectual disabilities.
Larson et al. in a meta-analysis to determine patterns of comorbidity among children aged 6–17 years in the United States of America observed that children with ADHD had at least one co-morbid condition like learning disability, conduct disorder and anxiety disorder [
28]. Spencer et al. [
29] has reported that opposition defiant disorder and conduct disorder co-occurred in 30–50% of children with ADHD. Adewuya et al. in a study among Nigerian school children of aged 7–17 years found that opposition defiant disorder, conduct disorder and anxiety disorder were co-morbid in those with ADHD [
9]. The co-morbid conditions differ in these studies as we may speculate that clinicians may be reporting only dominant comorbidities among this population.
This study had the following limitations: recall bias for mothers, especially regarding vaginal discharge and delayed milestones. It is especially difficult to establish an ADHD diagnosis in children younger than age 4 or 5 years, because their characteristic behavior is much more variable than that of older children. However, in this study only a few children were less than 5 years. We did not describe comorbidities like tic or anxiety disorders. The associated factors that were found to be significant in this study would require more exploration so that more information to be obtained from caretakers of study participants to ascertain their true associations, given that this was cross-sectional survey and it may not clearly explain these associations from our results.
Despite these limitations, this study is important because it is the first study in Uganda that estimated the prevalence and the associated factors of ADHD among children. Also, study participants who were presumed to be having ADHD using the DBRS were re-assessed by the child psychiatrist to confirm the diagnosis based of ADHD and its co-morbidities.