Differential diagnosis in neurodivergent patients: What looks similar does not have to be the same
The diagnosis of neurodivergent patients can be particularly challenging in adulthood. Concentration problems, social difficulties, sensory sensitivity, emotional dysregulation, or a need for routines are not specific features of a single diagnosis. They can occur in autism spectrum disorder (ASD), ADHD, anxiety and depressive disorders, obsessive-compulsive disorders, trauma-related disorders, or personality disorders.
For psychotherapeutic practice, this means: It is not the individual symptom that is crucial, but its developmental course, its function, and its context.
Developmental course instead of snapshot
ASD and ADHD are neurodevelopmental disorders. Therefore, it is of central importance in diagnosis whether relevant features have already existed in childhood and adolescence.
Especially in adults, the current symptomatology may be altered by compensation and adaptation strategies. A non-conspicuous clinical observation does not automatically rule out an ASD. Conversely, a conspicuous screening value is not sufficient for a diagnosis. Therefore, the diagnosis should bring together various sources of information and consider the entire developmental course.
Helpful questions include:
What particularities existed in childhood and adolescence?
What were social relationships and academic demands like?
Were there early difficulties with attention, organization, or impulse control?
How were changes, routines, or sensory stimuli handled?
What compensation strategies have been developed throughout life?
ASD, ADHD, or both?
ASD and ADHD show a significant phenomenological overlap. Difficulties with attention, self-organization, impulse control, or emotional regulation can occur in both disorders. At the same time, ASD and ADHD can also coexist.
In differential diagnosis, it should therefore not be asked which disorder a single symptom "belongs" to. What is crucial is the entire pattern.
In cases of attention problems, for example, it may be relevant whether these have existed since childhood and across situations or have only appeared in connection with depression, anxiety disorders, or other stressors.
In social difficulties, the question arises whether there are primarily difficulties in social communication, whether social situations are avoided due to fear of negative evaluation, or whether multiple factors are interacting.
Common differential diagnoses
Anxiety and depressive disorders can also produce features that appear neurodivergent at first glance. Concentration problems, social withdrawal, or exhaustion must therefore always be considered in a temporal context.
A similar challenge exists in distinguishing between ASD and obsessive-compulsive disorder. Routines and repetitive behaviors can occur in both. What is crucial, among other things, is their function: Do they serve, for example, to create predictability and regulation or to reduce compulsive anxieties?
Personality disorders are also among the relevant differential diagnoses. There are both overlaps and possible comorbidities. Therefore, an already existing diagnosis should not be hastily used as an explanation for all difficulties.
In trauma-related disorders, social avoidance, hyperarousal, sensitivity to stimuli, or difficulties in emotion regulation may be at the forefront. It is particularly important to clarify, when the respective features first appeared.
What is part of a sound differential diagnosis?
A careful diagnosis should connect various sources of information:
clinical history and current symptomatology
developmental and school history
standardized screening and diagnostic instruments
information from the social environment, if available
current functional impairments
systematic examination of relevant differential diagnoses and comorbidities
A screening can provide an important clue, but it does not replace clinical diagnosis. Standardized diagnostic procedures should also always be interpreted in the context of the history and the overall clinical picture.
The overall clinical view remains crucial
Especially with complex adult patients, there is rarely one finding that makes the diagnosis clear. Therefore, contradictory information is not unusual.
The central question is not: “Which test is correct?”
But: "How can the various findings be explained in the context of individual developmental history and diagnostic criteria?"
Good differential diagnosis therefore takes into account both neurodevelopmental peculiarities and psychological comorbidities. The goal is not only to achieve the most precise diagnosis possible but also to create a case concept that makes the actual difficulties of the patients understandable and enables appropriate therapeutic planning.
Sources
Arbeitsgemeinschaft der Wissenschaftlichen Medizinischen Fachgesellschaften (AWMF): S3-Leitlinie „Autismus-Spektrum-Störungen im Kindes-, Jugend- und Erwachsenenalter – Diagnostik“.
Carroll, H. M., Thom, R. P. & McDougle, C. J. (2025). The differential diagnosis of autism spectrum disorder in adults. Expert Review of Neurotherapeutics, 25(6), 635–648.
National Institute for Health and Care Excellence (NICE): Autism spectrum disorder in adults: diagnosis and management (CG142).
National Institute for Health and Care Excellence (NICE): Attention deficit hyperactivity disorder: diagnosis and management (NG87).
Taurines, R. et al. (2012). ADHD and autism: differential diagnosis or overlapping traits? A selective review. BMC Medicine, 10, 155.
World Health Organization (WHO): Clinical descriptions and diagnostic requirements for ICD-11 mental, behavioural and neurodevelopmental disorders (2024).