Diagnosing ADHD Comprehensively

ADHD is a very complex condition. Two important concepts are vital to understand when it comes to diagnosis and in unpacking the complexity of ADHD– differential diagnosis and comorbidity.

Differential diagnosis is the process of identifying an underlying condition that manifests in symptoms similar to that of ADHD, but these conditions explain the symptoms better than a diagnosis of ADHD, and ADHD should not be diagnosed.

Comorbidity is the co-occurrence of ADHD with other conditions.

Understanding how ADHD can be different to (differential diagnosis) and related to (comorbidity) other conditions is key to understanding the complexity of an ADHD diagnosis.

Differential Diagnosis

Differential diagnosis is the process of distinguishing between conditions that share similar symptoms. A formal assessment is needed in order to make a differential diagnosis. This is best carried out by a clinician, who is equipped with the right tools and training to identify the existence of different conditions. Generally, differential diagnosis is important for identifying any pre-existing conditions that underlie a person’s symptoms. To provide a simple example, the symptom of a cough can be caused by many conditions: from a common cold, to seasonal allergies, to something much more serious, such as lung cancer. It is then the job of the clinician to perform a comprehensive assessment to isolate the cause of the cough, ruling out the possibility of other illnesses that could cause the cough.

Similarly, the symptoms associated with ADHD can also be caused by other conditions. For example, inattention – a common symptom of ADHD – can also be caused by a variety of other conditions (see figure below). Thus, it is the clinician’s job to conduct a precise and accurate assessment to rule out the possibility of underlying disorders that manifest as ADHD-like symptoms. Differential diagnosis is especially important for ADHD as the symptoms have a high overlap with the symptoms of many other disorders. In the next block, we’ve outlined some disorders that may look like ADHD, but would require differential diagnosis.

Figure 1: some examples of a few disorders that may present as ADHD (Note this list is not exhaustive)

ADHD Versus Mental Disorders

There is a very high overlap between the symptoms of ADHD and that of other conditions. Clinicians should be equipped with a high level diagnostic ability to discern if an ADHD diagnosis is appropriate, or if the symptoms best fall under another disorder. It is important to have an accurate diagnosis before treatment commences; a thorough understanding of the condition allows for more tailored treatment, thus facilitating the best treatment outcomes. Moreover, appropriate treatment for underlying disorders often leads to the attenuation of ADHD symptoms.

Examples of some disorders that may present similar to ADHD are listed below:

Bipolar disorder: Manic episodes in bipolar disorder and ADHD both characterise impulsivity, talkativeness, distractibility, increased activity, physical restlessness and social disinhibition. While these symptoms occur episodically in bipolar disorder, these symptoms are chronic in people with ADHD.

Depression: Symptoms of depression may include executive function impairments, such as working memory and cognitive control, and may also include inattentiveness. These, too, are core symptoms in ADHD. However, people diagnosed with a depressive disorder typically do not experience hyperactivity, which is common in ADHD.  It is important to determine when the onset of depression arose, and whether the symptoms of inattention only arose after the onset of depression. As ADHD is a developmental disorder the symptoms of inattention, hyperactivity and impulsivity should be present from extremely young ages. Depression usually arises much later, rarely before the ages of 9 or 10 years.

Anxiety: People with anxiety disorders may also experience difficulties with sustained and selective attention, which is a core symptom of ADHD. Moreover, both anxiety and ADHD may interfere with one’s social relationships. However, many cognitive dysfunctions related to memory and executive function are different in anxiety and ADHD. Anxiety can arise earlier than depression, and you can have children who are very nervous and scared, so the effects of anxiety on attention in very young ages can be harder to determine. What is however important to consider is whether the attention issues are only present during periods of heightened anxiety and whether when relaxed and calm the person can focus much better.

Borderline Personality Disorder: BPD can be associated with heightened impulsivity which is characteristic of ADHD-Hyperactive Impulsive Presentation. However the profile of BPD is more diverse with issues with mood swings, anger and irritability. they tend to have tumultuous relationships and a fear of abandonment. There is often cutting, suicidal thoughts and a certain level of paranoia. Low self-esteem and a distorted sense of self are often present.

ADHD Versus Physical Issues

Sleep Disorders: Sleep disorders can often interfere with a range of cognitive and behavioural functions. The most common type of sleep disorder to create attention problems is obstructive sleep apnoea (OSA); a condition where the airway is obstructed during sleep. Common symptoms include excessive snoring, fragmented sleep and daytime sleepiness. During sleep, obstructions to the airway lead to period of hypoxia, where the brain is deprived of oxygen supply. People with OSA may experience  decreased attention span, poor memory and problems with executive functions. However, getting appropriate sleep treatment, such as continuous positive airway pressure (CPAP) therapy, will often improve these ADHD-like symptoms (although improvement may take a few months if this has been an ongoing issue).

Other issues with sleep can include sleep onset disorder (ie. issues falling asleep) as well as sleep maintenance disorder (issues staying asleep and waking in the night). Both of these disorders can result in poor sleep, fewer hours sleep, and fatigue during the day. Less sleep is associated with cognitive issues such as poor attention. If there are concerns with sleep and attention issues, best to treat the sleep issues as a priority and then determine whether the attention issues remain. Note: It can taken several weeks to months to see improvements in attention if there is a sleep disorder, and the longer the sleep disorder has gone on, the longer it will take to get good brain recovery.

Medications: Many medications have as a warning ‘may cause drowsiness’. If one is taking a medication daily then one should consider whether this medication is affecting attention skills and creating symptoms of ADHD.

Absence Seizures: Over the years we have seen several children who have come in for ADHD assessments and during the assessment they are generally attentive and then become completely unfocused and unresponsive for a brief period. In some cases you could see their eyes flicker slightly, but in none of these children did they look highly unusual to the non-trained eye. These children were diagnosed with a type of epilepsy called absence seizures. After the seizures inattention then became more pronounced, which is very common after a seizure. If you see this person staring as if in a trance, and being unresponsive for 5-15 seconds (typically), you should speak to your GP about a referral to a neurologist.

Various Medical Disorders: Many medical disorders can make you feel awful, irritable and tired. Low energy and needing to sleep is a common way the body responds when sick in order to help the body rest and promote healing. Thyroid issues are one type of common disorder than can get diagnosed as depression or we have even had a few referrals questioning ADHD. If you have other medical symptoms along with inattention or fatigue we recommend a general health check up by your GP along with blood tests or other recommended tests so make sure there are no medical issues that may be causing current symptoms of inattention.

ADHD versus Sensory Processing Issues

Sensory processing is important for everyday functioning; it is how the brain transforms signals from the environment into meaningful information. Problems with sensory processing, especially if they are present in childhood, can interfere with the typical development of cognitive and behavioural functioning.

Visual Processing: People with visual processing problems may show symptoms of inattentiveness in relation  to visual information. We have over the years seen many children who have been struggling to focus and when assessed it was found that all their issues were visual in nature. They were then referred on to optometrists/ orthoptists/ behavioural optometrists who then diagnosed visual issues. Following treatment by these clinicians the attention issues resolved. There are numerous types of visual processing issues that people can present with such as convergence, divergence, fixation and other ocular-motor movement disorders. On a basic level people can have issues with their eye muscles, which may be fatiguing when having to fixate in a single place, or when required to read and track visual information for extended period. These people may struggle to maintain their visual focus when reading or looking at visual information. They may need to move their focus into the distance to ‘reset’ their eyes and relax their muscles. While appearing to fit some of the symptoms of ADHD, these symptoms are related to difficulties in visual processing. Left untreated, visual problems in childhood can lead to a lifetime of attentional problems, which can be misdiagnosed as ADHD. Note: these higher level visual issues are not related to basic visual acuity for which glasses are usually prescribed. These visual issues are usually much more subtle and can be missed by basic optometrists as they are often not trained in this more intensive type of assessment.

Auditory Processing Issues: Children with patterns of ear infections that may have led to hearing loss (usually requiring the insertion of grommets), are at a higher risk for auditory processing difficulties. These may include issues with hearing certain sounds, frequencies or even hearing speech when there is background noise. This can then create issues with maintaining focusing when listening to people speak, especially when there is background noise. This can again look like ADHD, but it is usually evident that the issues are more auditory in nature, and visual attention is usually uncompromised.

Note: Treatment of visual and auditory issues need to be done a a basic processing level. Classic ADHD medications can help with these issues as they can give the person more mental energy to be able to persevere with these processing issues, however it is better to try and treat the core issue in these cases rather than mask them with medication. If you are concerned you may have either visual or auditory processing issues, or even basic vision or hearing problems, having these assessed first can minimise the risk of misdiagnosis.

ADHD vs Other Neurodevelopmental Disorders

Intellectual Disability: When a person has overall low functioning an IQ test should be conducted before a diagnosis of ADHD is even considered. For example, if someone has poor language and poor comprehension skills, along with very low learning capacity, and generally struggles with memory and other cognitive skills, a broader intellectual assessment should be conducted. ADHD should not be diagnosed in case where low IQ or an intellectual disability better account for the attention weaknesses. Often psychologists will conduct an IQ test as part of every ADHD diagnosis, not just to look at overall functioning, but also to look to see if there are any specific weakness on a general screening that may not just be related to attention. IQ tests can screen for potential language issues, visual processing issues as well as general intellectual concerns. Typically in people with ADHD measures of working memory and processing speed are lower compared to more abstract reasoning skills and this can be used to supprt a diagnosis of ADHD if these issues are found.

Language Disorder: Standard IQ tests also have measures of verbal skills, and if these areas come out very low compared to other skills referral to a speech therapist to assess for a language disorder should be considered before. Receptive language disorders reflect deficits in being able to comprehend verbal language. As one can imagine if a child has issues comprehending what they are hearing, they will struggle to pay attention, and will appear as highly inattentive. This will be present both at home, and particularly in the classroom. This is likely to affect reading comprehension and general learning, and the deficits are likely to be more widespread than ADHD alone. If there are language concerns these will need to be formally assessed and considered as a differential diagnosis before ADHD is diagnosed.

Autism Spectrum Disorder (ASD): Prior to the latest DSM diagnostic criteria (Edition 5), one could not be diagnosed with ADHD if they had ASD. Since 2013 this requirement has now been removed as it has been recognised that many people with ASD also have ADHD. It is however still important to consider if there are signs. People with ASD and ADHD can both have significant social issues, although they are usually quite different in nature. It is usually more helpful to screen the non-social issues as these are more unique to ASD, such as have issues with flexible behaviour, being rigid, having repetitive motor movements, having fixations/obsessions, or having sensory issues. Often in the context of having both ADHD and ASD, it is the ASD that often causes more severe issues and is seen as the primary diagnosis. Whilst there are numerous medications and types of therapy for ADHD that can normalise some functioning, unfortunately the prognosis in ASD is often more severe and there are no medications for it. People with more severe levels of ASD can access the NDIS in Australia, and hence getting this diagnosis first is helpful as the NDIS may then pay for additional assessment and therapies. Unfortunately, the NDIS does not fund ADHD as a stand alone disorder. See NDIS for more details : https://www.ndis.gov.au/.

Procedures for Assessing ADHD?

Standardised Attention & Executive questionnaires

In order for ADHD to be even considered as a diagnosis according to the international benchmark of diagnosis (DMS-5), a minimum of 6 criteria for inattention symptoms (5 for adults) &/or 6 criteria for hyperactive/impulsive symptoms (5 for adults) need to be met, in TWO OR MORE areas (e.g.., home, work etc). To make this as objective as possible it is recommended that standardised forms are completed by multiple people. In the case of a child as a minimum this should include at least one parent and a teacher who knows them well.  If the child is old enough then can also complete a self-rating. For an adult this should include a self-rating as well as an observer rating where possible. Also having a parent of an adult complete a rating based on symptoms they noted prior to age 12 is important as this is a critical part of the ADHD criteria (ie. that the symptoms were present before age 12).

We recommend that these rating scales  are standardised. Standardised questionnaires compare the person to people the same age, which gives you a score not only of whether they are meeting criteria, but also how severe the issues are. Some people may meet criteria, but there scores are only very mild and are not really at any significantly disordered level. Standardised scores are also a very good way of then precisely measuring changes following any interventions.

Two of the most commonly used standardised questionnaires in adults are the Conners Adult ADHD Rating Scale (CAARS) and the Behaviour Rating Inventory of Executive Functioning (BRIEF). In children there are several Conners scales (Comprehensive Behaviour Rating Scales and the shorter Conners 3), as well as the BRIEF and CEFI. We recommend for children the longer Conners form (CBRS) as this actually screens for ADHD as well as several behavioural disorders (ODD,CD), anxiety disorders (OCD, GAD, phobias), major depression and even Autism Spectrum. This can be important to have formulate a comprehensive diagnosis of comorbidities or consider other differential diagnoses.

Formal Attention & Executive Assessment

If enough evidence is present at the initial consultation and standardised rating questionnaires,  the clinician can perform a formal cognitive assessment in order to determine the precise processing issues underlying the noted problems. Common tests include:

Intellectual Functioning: Weschler Scales (adult, child or preschool). These measure verbal intellect/reasoning,  nonverbal intellect/reasoning, working memory, processing speed and some versions measure visual-spatial skills/

Objective Attention & Executive Testing

Domains may include:

• Sustained attention (Visual & auditory)
• Switching attention (Visual & auditory)
• Selective attention (Visual & auditory)
• Impulse control (Visual & auditory)
• Attention Span (Visual & auditory)
• Working memory (Visual & auditory)
• Planning
• Time management
• Perseveration
• Strategy generation
• Self-monitoring

Other Processing Tests to Make a Differential Diagnosis

If issues are noted on an initial consultation with any of the following, specific tests should be added to the battery to precisely evaluate the full cognitive profile.

Learning/ academic assessment: If issues are noted with learning or academic skill, and concerns are present regarding a potential learning disability, a concurrent learning disability assessment can be conducted as part of the ADHD assessment. Areas tested could include: Reading tests (decoding, comprehension, reading fluency and speed), Writing tests (spelling and essay composition), Numeracy tests. One of the most commonly used tests in Australia is the Weschler Individual Achievement Test- Version 3.

Memory: If issues are noted with significant levels of memory problems, formal memory testing may be recommended. Most of the time issues with memory are more related to issues with attention processing and encoding of the information, rather than true memory retrieval. That is, the information was never properly laid down in memory stores in the first place. However, for people who are highly forgetful the following tests may also be recommended: Visual immediate memory (memory encoding), Verbal immediate memory (memory encoding), Visual delayed memory (retrieval), Verbal delayed memory (retrieval), Visual recognition memory (retrieval vs encoding), Verbal recognition memory (retrieval vs encoding). Common tests include the WRAML, Children’s Memory Scale, Weschler Memory Scales.

Visual processing: If issues are noted with vision such as skipping lines when reading, having problems maintaining eye contact with visual tasks or other people, seeing fine details, missing social cues, struggling with remembering visual information etc., visual assessment will also be conducted. Both functional visual issues (issues with occular-motor movement) as well as higher level visual issues (eg. discrimination, spatial skills, figure-ground) can be assessed. Sometimes visual issues can explain the issues with focus, and if all visual issues are visual in nature this should be assessed and treated (if required) before a diagnosis is confirmed).

Auditory processing: If issues are mainly noted with attention when listening to information, particularly when there is background noise, the primary issue may be one of auditory processing rather than a true attention deficit. Hence tests of basic auditory processing, auditory figure ground should be screened. If issues are found referral to an audiologist may be recommended.

Neuromarkers on Brain Scans

Whilst brain scans are not diagnostic in regards to ADHD, there is a large push in the scientific field to try and find a biomarker on a brain scan so that ADHD can be diagnosed in a more objective manner. In the same way a blood test can be use to identify diabetes or high cholesterol, it is recognised that we need some form of measure of the brain if we ever want to be able to diagnose ADHD with a high level of objectivism. Technically a brain scan could be a very useful tool in the future in understanding whether issues are noted at a physiological level. The most commonly researched scan is the EGG, often using quantitative methodology (ie. qEEG).  There are several different brainwave patterns noted in patients with ADHD, and there are some (although limited) centres conducting these types of scan in Australia. We are excited to see where this field goes, and the AAI is actively researching this area with great interest.