Intellectual developmental disorder in adult psychiatry: A 24-year register study

Background: Intellectual developmental disorder (IDD) may pre-dispose for mental health disorders. It is sometimes debated whether the needs of this group are adequately met in general psychiatry. However, little is known about patients with IDD in the psychiatric clinical setting—occurrence, clinical diagnoses, or service use. Aims: This study aimed to assess the number of adult patients diagnosed with IDD in a psychiatric clinic, their psychiatric diagnoses, and their use of psychiatric services. Methods: Individuals with registered IDD diagnoses were identified in a university hospital adult psychiatric clinic register comprising 67 384 patients. Results: IDD had been diagnosed in 0.6% of the patients. Psychotic disorders were the most common co-existing psychiatric diagnoses (25.5%). In 21.8% no psychiatric diagnosis other than IDD was registered. More than 50% had been inpatients; 21% had been compulsorily admitted. Patients with IDD had required a mean of five hospital beds per day. Conclusions: The percentage, 0.6%, of IDD diagnoses was lower than estimates of the prevalence of IDD in the general population. This may reflect a lower need for psychiatric care, barriers to access services, or diagnostic over-shadowing. One fifth of the patients in this study had no psychiatric diagnosis beside IDD, which may be due to diagnostic difficulties, or other problems (e.g. somatic or behavioural disorders) leading to psychiatric contact. Since patients with IDD use the equivalent of five inpatient beds every year, it is suggested that it may be worthwhile to consider specialized psychiatry with expertise in IDD, even though this group is small.