Differential diagnostics for ADHD

Author: Ulrich Brennecke
Review: Dipl.-Psych. Waldemar Zdero

A careful diagnosis of ADHD always requires a thorough differential diagnosis to rule out other disorders with similar symptoms.

The prevalence of mental disorders overall is quite high in Germany at 33.3% within one year (EU: 38.8%).

Important factors that should be considered in the differential diagnosis of ADHD are, for example, acute stress reactions, unrecognized giftedness or underachievement, organic primary disorders such as sleep disorders or post-commotional syndromes or medication side effects.
Mental and psychiatric disorders whose symptoms can resemble ADHD include anxiety disorders, affective disorders, autism spectrum disorders (ASD) and borderline personality disorder (BPD).
The percentages in brackets after the headings indicate the population prevalence, i.e. they are independent of ADHD.

• 1. Differential diagnostics
  • 1.1. Differential diagnosis
  • 1.2. ADHD (ASD, OCD) - homogeneous disorders or purely dimensional grouping?
  • 1.3. Comorbidity: the difference to differential diagnosis
  • 1.4. Prevalence: frequency of mental disorders
• 2. Differential diagnosis for ADHD
  • 2.1. “Healthy“ stress reaction to a stressful situation
  • 2.2. Age-appropriate high activity level
  • 2.3. Primary organic disorders
  • 2.4. Side effects of medication
  • 2.5. Mental and psychiatric disorders

1. Differential diagnostics¶

1.1. Differential diagnosis¶

Differential diagnosis means making sure that the symptoms are not (also) caused by other causes or disorders and consequently require different treatment.

1.2. ADHD (ASD, OCD) - homogeneous disorders or purely dimensional grouping?¶

One study attempted to assign 238 people with ADHD, ASD and OCD who showed different symptoms or were healthy controls to homogeneous disorder groups based on cortex thickness in 76 cortex regions. This was done using machine learning (weak AI). No homogeneous groups could be formed.¹
This indicates that the individual differences between people with ADHD are greater than the similarities.

1.3. Comorbidity: the difference to differential diagnosis¶

While differential diagnosis means checking whether the symptoms that (here:) point to ADHD might not actually be caused by another problem, i.e. that there is no ADHD, comorbidity means that someone who suffers from one disorder (here: ADHD) is also (additionally) affected by another disorder or illness.

Comorbidity with ADHD therefore means that (here:) ADHD has been clearly identified and other problems exist in addition to ADHD.
Many disorders have very typical comorbidities - including ADHD, so it is always necessary to check these as part of a proper medical history. ⇒ ADHD - comorbidity

Most comorbidities typical of ADHD may have gene variants in common with ADHD or the common cause of early childhood stress exposure that meets a gene predisposition specific to the respective (co-)morbidity.
⇒ How ADHD develops: genes + environment

1.4. Prevalence: frequency of mental disorders¶

33.3% of all Germans and 38.8% of all EU citizens suffer from a mental disorder (within 12 months). Men and women are affected in roughly equal numbers, but with different types of disorder. The age group of 18 to 34 years is most frequently affected.²
Of these 33.3%, 1/3 (i.e. a total of 11.1% of all Germans) suffer from more than one Disorder. In these cases, there is an overt comorbidity of several disorders from different diagnostic groups. The comorbidity with regard to different individual diagnoses from the same group is significantly higher again.
Comorbidities increase with age.²

For comparison with the prevalence values (frequency of occurrence) given below:
ADHD has a prevalence of

• Children and young people together 5.29 %
  according to an international long-term meta-analysis of 102 international studies with n = 171,000 subjects³
  • Preschool children: approx. 3 %⁴
  • Young people: approx. 8 %
    • Boys approx. 6 %⁴
    • Girls approx. 2 %⁴
      (We suspect that girls are more likely to go unrecognized due to the ADHD-I subtype being more common in them)
• Adults:
  • Approx. 1 - 4 %⁴
  • Approx. 3 - 5 %⁵

This would make the lifetime prevalence of ADHD roughly equivalent to that of diabetes.⁶

Friedmann reports that the lifetime prevalence of ADHD in the US has risen from 7.8% in 2003 to 11% in 2011.⁵
This is not the result of an increase in ADHD, but rather that ADHD is now better recognized and more reliably diagnosed.

Further information on the prevalence distribution of ADHD:⇒ Frequency of ADHD (prevalence)

2. Differential diagnosis for ADHD¶

The following phenomena should be checked when examining where ADHD-typical symptoms originate from.
The relevant sections have been moved to separate articles, which are linked below.

2.1. “Healthy“ stress reaction to a stressful situation¶

2.2. Age-appropriate high activity level¶

2.3. Primary organic disorders¶

2.4. Side effects of medication¶

2.5. Mental and psychiatric disorders¶