Attention-deficit/hyperactivity disorder (ADHD) and autism spectrum disorder (ASD) in adult psychiatry. A 20-year register study

Abstract

Objective: Attention-deficit/hyperactivity disorder (ADHD) and autism spectrum disorder (ASD) are increasingly recognized in adults. This study aimed to assess trends in diagnostic practice, diagnostic delay and comorbidity regarding ADHD and ASD in adult psychiatric patients.

Methods: Individuals with diagnosed ADHD or ASD were identified in an adult psychiatry register comprising 56,462 patients.

Results: ADHD was diagnosed in up to 2.7% and ASD in 1.3% of the patients. Most cases were diagnosed within 2 years of first contact with adult psychiatry, but some patients were treated for 10 years or more before being diagnosed with ADHD or ASD. Seventy per cent of ADHD and 56% of ASD patients were treated as outpatients only. Other psychiatric diagnoses were registered in about 60%. Affective disorders were common in patients with ADHD. Psychoses and intellectual disability were more common in ASD patients. Psychoactive substance use-related disorders were considerably more common in those with ADHD. Concomitant ADHD and ASD were seldom diagnosed in this clinical material.

Conclusion: ADHD and ASD were probably much underdiagnosed in the studied group of psychiatric patients. Other psychiatric diagnoses were common, but not ADHD with concomitant ASD.