1.2.2 ADHD and comorbidities
It is quite common to find that individuals with ADHD are also diagnosed with comorbid conditions. For example, autism is often comorbid with ADHD in children and adolescents, but there are other comorbidities too. The results of a study of 5028 children with ADHD in the US are shown in Figure 2 to illustrate this.
You might have heard of many of the conditions shown in Figure 2. The most prevalent comorbid condition shown in the figure is labelled ‘learning disability’. This category includes dyslexia, which can cause difficulties with reading and writing, and dyscalculia, where individuals have difficulty with numerical and mathematical concepts. The second most common comorbid condition is conduct disorder, which you may be less familiar with (although it was also mentioned by Dr Iris Rathwell in Activity 1). This is a condition associated with high levels of antisocial behaviour.
From Figure 2, can you identify any common features of the comorbid conditions shown?
They are all related to learning, behaviour or mental health.
In addition to the conditions shown in Figure 2, ADHD can also show comorbidity with physical conditions, for example asthma, obesity, irritable bowel syndrome and insomnia (Matza et al., 2005; Hodgkins et al., 2011).
Comorbid conditions may occur simultaneously but independently, or they may share a causal pathway, meaning they are not entirely independent of each other. So far, there is little understanding of the exact relationship between ADHD and the conditions that are commonly comorbid with it. A better understanding of the relationships can help scientists and healthcare professionals understand and treat the individual conditions and also to develop effective treatment for the two where they co-occur. The presence of comorbidities can also add another layer of complication to diagnosis, which, as you will see in the next section, is already quite complex.