The Diagnostic Overlap Problem: Why Misdiagnosis Is the Rule, Not the Exception
Most clients who arrive with a complex or treatment-resistant presentation haven't failed treatment. They've been treated for the wrong thing. The overlap between OCD, ADHD, eating disorders, and anxiety makes misdiagnosis not a clinical failure but a structural feature of how these conditions present.
Why these conditions overlap.
OCD, ADHD, eating disorders, and anxiety are not cleanly separable categories. They share neurological substrates, behavioral patterns, and phenomenological features that make differential diagnosis genuinely difficult not just for generalists, but for experienced clinicians who haven't seen enough presentations of each to recognize the variations.
The DSM categories are clinically useful, but they weren't designed to describe how these conditions actually appear in living people. A person with OCD and ADHD doesn't present as two discrete diagnostic pictures side by side. The conditions interact. The ADHD affects how the OCD presents. The OCD affects how the ADHD is experienced. The result is a clinical picture that fits neither diagnosis cleanly and that often receives the diagnosis the treating clinician is most familiar with.
The diagnostic errors that occur most often.
OCD diagnosed as generalized anxiety.
OCD is not an anxiety disorder, though it was historically categorized as one. The distinction matters clinically because treatment for generalized anxiety which targets the anxious cognitions and aims to reduce their frequency or intensity often makes OCD worse. OCD is maintained by the compulsion cycle, not by the anxious content alone. Treatment that doesn't target the compulsions doesn't interrupt the mechanism.
The distinguishing features: OCD doubt is intrusive, ego-dystonic, and returns despite reassurance. GAD worry tends to be more ego-syntonic the client recognizes it as their own thinking style and is more diffuse across life domains. OCD compulsions are organized around specific feared outcomes. GAD doesn't produce the same compulsive response pattern.
ADHD diagnosed as anxiety or depression.
Undiagnosed ADHD in adults is commonly accompanied by secondary anxiety and depression that develop in response to years of inconsistency, shame, and apparent underperformance. When clients present with this picture, the anxiety and depression are visible and the ADHD underneath them is not. Treatment addresses the secondary conditions. The primary condition remains unaddressed.
The distinguishing question: Is the anxiety produced by ADHD-generated consequences missed deadlines, forgotten commitments, the chronic gap between intention and action or is it primary? Anxiety that remits significantly when ADHD is effectively managed was not primary anxiety.
ADHD misread as trauma.
ADHD's emotional dysregulation, rejection sensitivity, difficulty with relationships, and history of shame and inconsistency can produce a trauma-like clinical presentation. Clients with undiagnosed ADHD have often experienced genuine relational and academic adversity as a result of the condition, which adds real trauma to the picture. The two are not mutually exclusive. But treating ADHD symptoms as trauma-based when they're neurobiologically rooted leads to trauma-focused treatment that doesn't touch the core deficit.
ARFID misread as picky eating or sensory issues.
ARFID in adults is underdiagnosed because the clinical literature focuses heavily on children, and because adults have developed sophisticated compensatory strategies that make the restriction less visible. An adult who has eaten from a narrow food list their entire life, who manages social eating through careful selection or advance research, and who doesn't experience significant distress about body weight or shape is often labeled a picky eater. The functional impairment and nutritional risk are missed.
What accurate assessment requires.
Differential diagnosis at the overlap requires two things that generalist training often doesn't provide: familiarity with how each condition presents in its more varied and subtle forms, and willingness to hold multiple hypotheses simultaneously rather than landing on the most available explanation.
Practically, this means asking about compulsions when the presentation looks like anxiety. Asking about executive function when the presentation looks like depression or treatment resistance. Asking about eating patterns and food history when the presentation involves ADHD. Asking about trauma when the presentation looks like pure ADHD. These conditions are not mutually exclusive, and the clinical instinct to find the most parsimonious explanation often produces an incomplete one.
For clients reading this: if you've had multiple diagnoses that haven't quite fit, or treatments that haven't worked the way they should, the diagnostic picture not your response to treatment may be where the problem lives.
