Types and causes of ADHD

It is important to have clarity regarding the different types of ADHD, since the way they present is different and more importantly the treatment – both pharmacological and non-pharmacological such as CBT, will vary with diagnosis. There are three main subtypes of ADHD.
Dr Pablo Jeczmien MD

Three subtypes of ADHD

There are three main subtypes of ADHD which can be diagnosed – knowing which you have is key to making sure that you have the right treatment plan.

1. ADHD – inattentive
   Inattentive ADHD - commonly known as ADD accounts for about 33% of all ADHD in adults. ADD or inattentive ADHD is characterised with difficulties staying focused and attending to daily, mundane tasks. Individuals may be easily distracted by irrelevant sights and sounds, bouncing from one activity to another or becoming bored quickly.
2. ADHD – hyperactive & impulsive
   Hyperactive and impulsive ADHD accounts for 7% of all ADHD in adults. The main symptoms are related to impulsivity and hyperactivity, whilst inattention may be secondary and not as much of a problem.
3. ADHD – combined
   Combined ADHD accounts for about 60% of all ADHD in adults and, as the name suggests, is a combination of inattention and hyperactivity/impulsivity.

What causes ADHD?

There is much debate as to the cause of ADHD in adults and most experts would say ADHD / ADD is caused by several factors which include:

1. Biological
   MRI scans have shown that the brain functions differently in someone with ADHD. For instance, children with ADHD show a delay (of about three years) in the development of the part of the brain that is involved in thinking, paying attention and planning. There are also overall delays in the maturation of the outermost layer of the brain, known as the cortex and some abnormal growth in the corpus callosum, which is the brain structure that is important for the communication between the two halves of the brain.
2. Hereditary causes of ADHD
   The genetic makeup of an individual can make someone more susceptible to ADHD. Research has shown that ADHD / ADD can run in families.
3. Environmental causes of ADHD
   It is thought that a mother who smokes, drinks of takes drugs during pregnancy may increase the risk of her child developing ADHD. There have also been studies showing a link between ADHD development and exposure to lead¹. Both of these factors impact on the way the brain develops as an embryo and in infancy. There are also thoughts that early childhood trauma, such as a chaotic family life, neglect or abuse can impact on the way a child’s brain develops and this can increase the likelihood of ADHD developing.
4. Integrative Medicine
   There is a growing body of evidence that microbiota /microbiome – the bacteria that we all have in our guts - plays an important role in mental health disorders and ADHD / ADD in particular. An imbalance of the microbiota affects, among other things, the levels of essential nutrients – minerals and vitamins – and as a consequence the production of neurotransmitters involved in our normal functioning, which can then result in impaired attention, hyperactivity and impulsivity.
5. Brain Injuries
   A very small percentage of ADHD cases are linked to brain injuries.

¹ Nomura, Y et al (1998)

Download our ADHD Assessment Guide

Whilst most of those with Hyperactivity/Impulsivity can present with different degrees of Attention deficits, this is not necessarily the case the other way around; many times the symptom of Inattention presents without the other elements. Further, in some cases Hyperactivity/Impulsivity might respond better to non-stimulant medications, rather than stimulants such as Methylphenidate. Knowing the type of ADHD you have is therefore important to getting effective treatment.

Dr Pablo Jeczmien

MD MRCPsych

Consultant Psychiatrist

Brighton

Dr Pablo Jeczmien is a Consultant Psychiatrist in General Adult Psychiatry for the Sussex Partnership NHS Foundation Trust. Dr Jeczmien has a medical degree and is a Member of the Royal College of Psychiatrists.