When someone seeks an assessment for ADHD or autism, they’re often looking for clarity.

They may have spent years wondering why everyday life feels harder for them than it seems to for other people. This might include difficulties with staying focused, managing emotions, coping with change, dealing with noise or busy environments, keeping organised, making friends, or understanding social situations.

For many people, an assessment can feel like an important step towards finally understanding themselves, or their child, better.

But a good assessment doesn’t only ask:

‘Is this ADHD?’

Or

‘Is this autism?’

It also asks:

What else might be going on?’

This is why the pre-assessment forms we ask patients to complete are so important.

We know these forms can feel long and sometimes repetitive. Some questions may be difficult to answer, especially if they ask about childhood, school experiences, family history, mental health, or day-to-day challenges. Patients sometimes wonder why so much information is needed before the appointment even begins.

The reason is that these forms help us build a fuller and more accurate picture. They allow us to understand not only the symptoms or traits someone is experiencing now, but also how long they’ve been present, where they show up, how they affect daily life, and whether something else may also be contributing.

They also help us use the assessment time more effectively. By reading the forms beforehand, your clinician can ask more focused questions, explore important themes in more depth, and avoid relying only on what can be covered in a single appointment.

Completing the forms as fully and honestly as possible can make a real difference to the quality of your assessment. It helps us understand you as a whole person, not just a list of symptoms.

This is where something called a differential diagnosis comes in.

 

What is a differential diagnosis?

A differential diagnosis simply means looking at different possible explanations for a person’s difficulties.

Many conditions can share similar signs. For example, difficulties with concentration may be linked to ADHD, but they can also be linked to anxiety, low mood, poor sleep, stress, trauma or a learning difficulty.

In the same way, finding social situations difficult may be linked to autism, but it can also be linked to social anxiety, communication difficulties, past bullying, low confidence, or feeling overwhelmed.

So, rather than jumping to one conclusion, your clinician takes time to understand the whole picture.

This may include:

  • What you were like as a child.
  • What school, work, home and relationships have been like.
  • Whether difficulties happen in one setting or several.
  • Whether there are sensory sensitivities.
  • Whether sleep, anxiety, mood or health problems may be involved.
  • Whether there are other neurodevelopmental differences, such as dyslexia or dyspraxia.
  • What your strengths are, as well as your struggles.

A differential diagnosis isn’t about dismissing someone’s concerns. It’s about making sure the explanation is accurate and helpful.

 

Why can ADHD, autism and other conditions look similar?

ADHD and autism can affect attention, emotions, behaviour, communication and daily life. But these areas can also be affected by many other things.

For example, a child who is distracted in class may have ADHD. But they may also be anxious, struggling to understand the work, having trouble sleeping, or feeling overwhelmed by noise in the classroom.

An adult who avoids social events may be autistic. But they may also have social anxiety, depression, trauma-related difficulties, or simply feel exhausted from trying to cope all day.

This is why context matters.

The same behaviour can have different causes in different people.

 

Conditions that can look like ADHD

ADHD can involve difficulties with attention, impulsivity, restlessness, organisation and emotional regulation. However, other conditions can create similar difficulties.

Anxiety

When someone is anxious, their mind may feel busy all the time. They may struggle to focus because they are worrying, overthinking or scanning for danger.

This can look like distractibility or restlessness.

Depression or low mood

Depression can affect concentration, motivation, energy and memory. A person may find it hard to start tasks, finish things, or keep up with daily responsibilities.

This can sometimes look like inattentive ADHD.

Sleep difficulties

Poor sleep can have a huge impact on attention, patience, memory and mood. Children who are tired may even appear more hyperactive rather than sleepy.

Before deciding that attention difficulties are due to ADHD, it’s important to understand sleep patterns too.

Trauma or chronic stress

People who have experienced trauma or ongoing stress may be constantly on alert. They may be easily startled, emotionally reactive, distracted, avoidant, or quick to feel overwhelmed.

These experiences can overlap with ADHD traits.

Learning differences

Dyslexia, dyscalculia, language difficulties or processing difficulties can make school or work feel much harder. A person may seem distracted or avoidant when the real issue is that they’re struggling to access the task.

Physical health issues

Pain, hearing or vision problems, thyroid difficulties, epilepsy, medication side effects, hormonal changes or substance use can all affect concentration, energy, emotions and behaviour.

 

Conditions that can look like autism

Autism can involve differences in social communication, sensory processing, routines, flexibility, interests and emotional regulation. But again, other things can sometimes look similar.

Social anxiety

A person with social anxiety may avoid social situations because they fear being judged, embarrassed or rejected.

An autistic person may avoid social situations because they feel confusing, unpredictable, exhausting or overwhelming.

The outward behaviour may look similar, but the reason behind it may be different.

OCD

OCD can involve repetitive behaviours, rituals and distress around uncertainty. Autism can also involve routines, repetition and a preference for predictability.

In OCD, rituals are often driven by intrusive thoughts or fears. In autism, routines may help the person feel calm, safe or regulated.

Communication difficulties

Some people have language or communication difficulties that affect how they understand others or express themselves. This can sometimes be mistaken for autism, or it may exist alongside autism.

Intellectual disability or developmental delay

Some people have broader developmental or learning difficulties that affect communication, independence and daily living. Autism may also be present, but assessment needs to take the person’s overall developmental level into account.

Mental health difficulties

Anxiety, depression, eating disorders, trauma and other mental health conditions can all affect social confidence, communication, flexibility, sensory tolerance and emotional wellbeing.

 

Can someone have more than one diagnosis?

Yes.

This is very common.

A person can be autistic and have ADHD. They can also have anxiety, depression, OCD, dyslexia, dyspraxia, sleep problems or other difficulties.

This is why assessment isn’t just about finding one label. It’s about understanding the person’s full profile.

Sometimes a diagnosis explains most of what someone is experiencing. Sometimes there are several things happening at once. Sometimes a person may not meet the full criteria for ADHD or autism, but they may still have very real difficulties and need support.

 

What should a good assessment feel like?

A good assessment should feel thoughtful, respectful and curious.

It shouldn’t feel like a tick-box exercise.

The clinician may ask about early childhood, school experiences, friendships, family life, work, relationships, mental health, physical health, sleep, sensory experiences and day-to-day coping.

They may use questionnaires, interviews, reports from school, information from parents or partners and clinical observation.

For children, it can be especially important to understand how they manage at home and school. Some children mask their difficulties in one setting and then become exhausted or distressed in another.

For adults, it can be helpful to explore how they’ve learned to cope over time. Many adults, especially women and people who were missed in childhood, may have developed strategies to hide or compensate for their difficulties.

 

Why does differential diagnosis matter?

Getting the right explanation matters because it helps guide the right support.

For one person, the next step may be ADHD medication, coaching and workplace adjustments.

For another, it may be autism-informed support, sensory strategies and help with communication needs.

For someone else, it may be therapy for anxiety, support with trauma, a sleep assessment, or screening for a learning difficulty.

The aim isn’t simply to give someone a label.

The aim is to understand what is really going on, so that support can be tailored to the person’s needs.

 

A final thought

Seeking an assessment can feel emotional. Some people feel hopeful, some feel nervous, and some worry they will not be believed.

Differential diagnosis isn’t about questioning whether your difficulties are real. It’s about taking those difficulties seriously enough to look at them carefully.

Whether the outcome is ADHD, autism, both, another explanation, or a combination of factors, the most important thing is that you come away with a clearer understanding of yourself or your child – and a better idea of what might help next.

 

Sources and further reading