Comorbidity patterns in children aged 6-12 years diagnosed with ADHD in South Kerala: a cross-sectional study

INTRODUCTION

Attention deficit hyperactivity disorder (ADHD) is a multifaceted neurodevelopmental disorder that affects individuals throughout the lifespan and is characterized by widespread heterogeneity in its underlying causes, clinical presentations, and responses to treatment.^1,2 ADHD is primarily characterized by persistent and developmentally inappropriate levels of inattention, hyperactivity, and impulsivity, arising from widespread and subtle alterations in gene expression across multiple brain regions that influence overall brain function.³ ADHD is most frequently diagnosed during the school years, although it can occur across all age groups. Growing evidence indicates that ADHD is a major contributor to the global burden of neurodevelopmental conditions among children and adolescents.⁴ An umbrella review of meta-analyses has reported considerable variability in the estimated prevalence of ADHD across studies ranging from 5.9 to 14%.⁵ Despite this heterogeneity, the global prevalence of ADHD among children and adolescents was estimated to be approximately 8.0% (95% CI: 6.0-10.0%).⁵

The prevalence of ADHD among children in India is consistent with the worldwide prevalence with some exceptions. In India, the reported point prevalence of ADHD among children and adolescents also shows wide variation, ranging from 1.3% to 28.9% across studies.⁶ The pooled prevalence has been estimated at 7.1% (95% CI: 5.1-9.8%), which is broadly comparable to global estimates. Sex-specific analyses indicate a higher prevalence among males (9.4%; 95% CI: 6.5-13.3%) than females (5.2%; 95% CI: 3.4-7.7%), with substantial heterogeneity observed across studies.⁶ This heterogeneity is often attributed to the presence of other childhood-onset conditions.⁷ Research suggests that approximately 60-100% of children diagnosed with ADHD also meet criteria for at least one comorbid disorder, many of which persist into adulthood.^7,8 Comorbidities associated with ADHD encompass a broad range of psychiatric, developmental, and neurological conditions, including oppositional defiant disorder, conduct disorder, anxiety and depressive disorders, learning disabilities, tic disorder, sleep disorders, and epilepsy, and is frequently associated with poor academic performance.^7-9 The presence of these comorbidities along with increasing the clinical heterogeneity of ADHD; also contributes to greater functional impairment, variability in symptom severity, and challenges in treatment and long-term outcomes.^7-9

ADHD frequently co-occurs with oppositional defiant disorder and conduct disorder, with comorbidity rates ranging from 30% to 50% in both epidemiological and clinical populations.¹⁰ Oppositional defiant disorder involves persistent patterns of negativistic, hostile, and defiant behaviour, whereas conduct disorder represents a more severe condition marked by chronic rule-breaking behaviours such as aggression, property destruction, deceitfulness, theft, and truancy.¹¹ Both disorders typically emerge before puberty, highlighting the importance of early identification and intervention to reduce the risk of long-term impairment, social dysfunction, and delinquent outcomes.^10,11 Anxiety disorders commonly co-occur with ADHD, with approximately 25% of children with ADHD meeting criteria for one or more anxiety disorders in both epidemiological and clinical samples.¹² This comorbidity is associated with greater psychosocial impairment, increased academic and behavioural difficulties, higher rates of additional psychopathology, and poorer long-term outcomes compared to ADHD alone.¹² Children with ADHD were also reported to have poorer cognitive and academic performance compared to their peers, including lower academic achievement, increased grade repetition, and greater need for special educational support.^11,13 An estimated 25% to 50% of people with ADHD also experience sleep problems, including insomnia, frequent awakenings, delayed bedtimes, and a higher risk of developing sleep disorders which often begin in childhood and may worsen with age.¹⁴ Sleep issues can further worsen core ADHD symptoms like focus, attention, and emotional regulation.¹⁴

ADHD being a clinically heterogeneous condition, often complicated by a range of comorbidities; screening for these comorbid conditions is essential to ensure appropriate management of children presenting with complex difficulties. Understanding the patterns and impact of comorbidity in ADHD is therefore critical for early identification, targeted intervention, and improving the overall prognosis of affected children. Our study therefore aimed to assess the comorbidities associated with children diagnosed with ADHD aged 6-9 years.

METHODS

The study adopted a cross-sectional design and was conducted at the child development centre (CDC); a tertiary care institution providing diagnostic and therapeutic service for children with neurodevelopmental disorders in south Kerala from June to December 2023.

The sample size was determined using Open Epi version 3.1, based on a previously reported prevalence of 31% ODD among children with ADHD from an earlier study.¹⁵ Using a 95% confidence level and an absolute precision of 6%, the required sample size was calculated to be 205 participants.

Children aged 6-9 years attending CDC clinics with a primary diagnosis of ADHD using INCLEN diagnostic tool for attention deficit hyperactivity disorder AIIMS modified (AIIMS-modified INDT ADHD tool) were consecutively included in the study.¹⁶ Children with audio-visual impairment, with IQ<85 and autism spectrum disorders were excluded from the study. Demographic details of the participants and developmental characteristics were assessed using a structured questionnaire. Children with the primary diagnosis of ADHD were administered Vanderbilt assessment scale-parent informant questionnaire to find out the type of ADHD (predominantly inattentive subtype, predominantly hyperactive/impulsive subtype or ADHD combined inattention/hyperactivity).¹⁷ Children’s sleep health questionnaire (CSHQ) was used to identify sleep problems.¹⁸ Epilepsy was diagnosed with the help of INDT-EPI tool.¹⁹ Psychopathological comorbidities like depressive disorder, anxiety disorder, Tic disorder, conduct disorder, and oppositional defiant disorder were diagnosed using diagnostic and statistical manual of mental disorders (DSM 5) criteria.¹ LD was assessed using The National Institute for Mental Health and Neurosciences index for Specific Learning Disabilities (NIMHANS SLD Battery).²⁰

Statistical analysis

Data were analysed using statistical software IBN SPSS version 26. Descriptive statistics were used to summarize demographic variables. The association between ADHD subtypes and comorbid conditions was examined using Chi-square tests of independence.

Ethical considerations

This study adhered to the ethical principles set forth in the Declaration of Helsinki. Ethical clearance was obtained from the institutional ethics committee before commencement of the study. parental written informed consent and participant verbal assent were obtained from all study participants.

RESULTS

The mean age of study participants was 7.1±1.0 years. The study included 206 participants, more than half were aged 6-7 years (65.5%) and predominantly males (85.4%). About 62.6% were living in rural areas and 40.3% belonged to nuclear families. Regarding birth and developmental history, 80.6% were full-term births, and 77.7% had normal developmental milestones. Most participants had normal vision (80.1%) and hearing (99.0%). The sociodemographic details of study participants are depicted in Table 1.

Among the 206 participants, the most common ADHD subtype was the combined inattention/hyperactive type, observed in 137 children (66.5%). Predominantly inattentive subtype was reported in 54 participants (26.2%), while the predominantly hyperactive/impulsive subtype was the least frequent, occurring in 15 participants (7.3%) (Table 2).

In the present study, oppositional defiant disorder (ODD) was the most common comorbidity, observed in 51 participants (24.8%) followed by conduct disorder (CD) in 15 participants (7.3%). Sleep-related comorbidities were identified, with clinically significant sleep disorders present in 16 participants (7.8%). Specific sleep problems included bedtime resistance in 14 (6.8%), sleep duration issues in 7 (3.4%), night walking in 5 (2.4%), sleep onset delay in 8 (3.9%), sleep anxiety in 10 (4.9%), parasomnias in 11 (5.3%), sleep-disordered breathing in 5 (2.4%), and daytime sleepiness in 12 (5.8%). Epilepsy was reported in 3 participants (1.5%). Specific learning disability (SLD) was present in 21 participants (10.1%), with dysgraphia in 5 (2.4%), learning difficulty in 6 (2.9%), and mixed learning problems in 10 (4.9%). Academic-related difficulties were highly prevalent, with problems in studies reported by 161 participants (78.1%). Poor academic performance was reported by 105 (51.0%), poor memory by 26 (12.6%), poor concentration by 114 (55.3%), and poor reading skills by 115 (55.8%) of children. However, other known comorbidities including depressive disorder, anxiety disorder and tic disorder were not found in the study sample (Table 3).

Association between ADHD subtypes and comorbid conditions

A statistically significant association was observed between ADHD subtypes and oppositional defiant disorder (ODD) (χ²(2) =20.35, p<0.001), with the highest prevalence noted in the combined ADHD subtype (45.3%), followed by the hyperactive-impulsive (26.7%) and inattentive subtypes (11.1%). A significant association was also found between ADHD subtype and conduct disorder (CD) (χ²(2) =8.99, p=0.01). CD was most frequently observed in children with the combined ADHD subtype (19.7%), while no cases were identified in the hyperactive-impulsive subtype. No statistically significant associations were observed between ADHD subtypes and other comorbid conditions.

DISCUSSION

The present study provides a comprehensive overview of the ADHD subtypes and associated comorbidities in children aged 6-9 years. The combined subtype predominated in the study group, with inattentive presentations also common while hyperactive/impulsive forms were less frequent. Comorbidities were prevalent, particularly disruptive behaviour disorders, with half of the children with oppositional defiant disorder. Conduct disorder was also found along with frequent sleep-related and academic difficulties. Specific learning disabilities were present in nearly one fourth of the children while epilepsy was rare. Anxiety-depressive and tic disorders were not observed. Overall, the findings highlight the clinical heterogeneity of ADHD and the importance of comprehensive assessment in this population.

Regarding ADHD subtypes, the combined inattentive and hyperactive/impulsive subtype was the most prevalent (66.5%), followed by the predominantly inattentive subtype (26.2%). This finding is consistent with previous studies reporting the combined subtype as the most common presentation in clinical samples. Clinical studies have also reported that the combined type is the most prevalent presentation, followed by the inattentive type, with the hyperactive/impulsive type being the least common.^21,22 The relatively lower prevalence of the predominantly hyperactive/impulsive subtype (7.3%) in children aged 6-9 years may be because hyperactive symptoms at this age often occur together with inattentive symptoms, leading to a higher proportion of combined presentations.

Comorbid conditions observed in our study underscores the clinical complexity of ADHD. Oppositional defiant disorder (ODD) emerged as the most common comorbidity (24.8%), followed by conduct disorder (7.3%). The significant association between ADHD subtypes and ODD, with the highest prevalence seen in the combined subtype, suggests that children exhibiting both inattentive and hyperactive-impulsive symptoms are at greater risk for oppositional behaviours. Similarly, the significant association between ADHD subtype and conduct disorder, predominantly affecting the combined subtype, highlights the need for early identification and targeted behavioural interventions in this group. Numerous studies have reported comorbidities, overlapping symptoms, and shared risk factors among cases of ADHD, oppositional defiant disorder and conduct disorder both in clinical and epidemiological samples.²³ Twin and family studies indicate strong genetic contributions to ADHD and shared familial aetiology with ODD and CD, with particularly strong genetic links between hyperactive–impulsive ADHD and both ODD and CD.²⁴ Prior findings demonstrate that combined and hyperactive ADHD subtypes present with behavioural problems supporting emotional dysregulation as a core component of ADHD with comorbid disruptive behaviour disorders.^25,26

Sleep-related problems were identified in a considerable proportion of participants, with bedtime resistance, parasomnias, sleep anxiety, and daytime sleepiness being commonly reported. Sleep disturbances in children with ADHD have been widely documented and may exacerbate core ADHD symptoms, impair emotional regulation, and negatively affect academic performance.²⁷ Although sleep disorders were prevalent, no significant association with ADHD subtypes was observed, suggesting that sleep problems may be a common pervasive issue in ADHD irrespective of subtype.

Specific learning disabilities were found in our study with mixed learning difficulties being the most frequent. Additionally, academic difficulties were found in more than three fourth of the study participants including problems in studies poor concentration, poor reading skills, and poor academic performance. Overall, there is an estimated comorbidity rate of 31 to 45% between SLD and ADHD in previous studies.²⁷ These findings reinforce the strong relationship between ADHD and academic underachievement and emphasize the need for comprehensive educational assessment and individualized academic support. Epilepsy was identified in a small proportion of children consistent with previous studies reporting a modest but notable association between ADHD and seizure disorders.²⁸ While no subtype-specific association was found, the coexistence of epilepsy further complicates clinical management and necessitates a multidisciplinary approach. However, other known comorbidities including depressive disorder, anxiety disorder and tic disorder were not found in the study sample.

The relative absence of certain psychiatric comorbidities observed in the present study may be partly attributable to the age range of the study population. Several comorbid conditions, particularly internalizing disorders such as anxiety and depression, tend to emerge or become more clinically evident at later developmental stages. As assessments in this study were conducted during an early phase of childhood, some conditions may not yet have fully manifested or may have been less readily detectable, potentially leading to an underestimation of their prevalence compared with reports from studies including older children and adolescents. However, the study provides valuable insight into the early clinical profile of psychiatric comorbidities in young children with ADHD, underscoring the importance of early identification and assessment.

CONCLUSION

Overall, the findings of this study highlight the high burden of comorbidities, particularly disruptive behaviour disorders and academic difficulties, among children with ADHD, especially those with the combined subtype. Early screening for comorbid conditions, along with integrated behavioural, educational, and family-based interventions, is essential to improve long-term outcomes in this population.

Funding: No funding sources

Conflict of interest: None declared

Ethical approval: The study was approved by the Institutional Ethics Committee

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