Autism in a Psychiatric Inpatient Population

Background: Previous studies suggest that autism spectrum disorders (ASD) are over-represented and under-diagnosed in adult psychiatric populations.  Adults in state psychiatric hospitals, many of whom received their diagnoses prior to the changing conceptualization and increased awareness of ASD, may have undiagnosed ASD. ASD symptoms may appear similar to the negative symptoms of schizophrenia. Four studies have estimated the prevalence of ASD in adult psychiatric populations (inpatient and outpatient) to be between 0.6% and 5.3%; no more than 10% of subjects in these studies who were found to have ASD were previously diagnosed as such. Instead, they were most commonly diagnosed with schizophrenia.

Objectives: The objective of this study was two-fold: to validate the previous prevalence estimates of ASD among psychiatric inpatients and to identify characteristics that discriminate between severely impaired adults with ASD and other psychiatric disorders.

Methods: The sample included 322 civilly-committed patients in one state psychiatric hospital in Pennsylvania.  Nursing staff completed the Social Responsiveness Scale (SRS) for each patient as part of standard of care. All patients with scores ≥ 100 on the SRS and a stratified random sample of those with lower scores were consented to conduct in-depth chart reviews and contact family members to conduct the Autism Diagnostic Interview-Revised (ADI-R). Chart reviews focused on developmental history, paying particular attention to age of onset and clinical features indicative of ASD.  Data on medications, self-injurious behaviors, and physical/mechanical restraints were collected for each consented patient.  Patients also completed clinical interviews and a neurobehavioral battery to assess the presence and severity of psychotic symptoms and cognitive impairment.  Case conferences with two psychiatrists and the team of assessing psychologists were held for all patients. 

Results: Eighteen percent of patients received a SRS score ≥100. ADI-R administration and case conferences are ongoing. Of the patients with completed case conferences (n=108), 9% meet criteria for certain or highly probable ASD. Formal analysis of characteristics that discriminate between severely impaired adults with ASD and other psychiatric disorders is ongoing.  Preliminary results indicate that unresponsiveness to medications, lack of recreational drug use, and documentation in charts indicating that the patient “responds to internal stimuli” but no clear documentation of hallucinations/delusions discriminate between the presence of ASD and other psychiatric disorders.

Conclusions: Almost one in 10 adults in this state psychiatric hospital met criteria for ASD, a much larger proportion than has been found in most previous studies. Previously validated screening and diagnostic instruments including the Social Responsiveness Scale (SRS) and the Autism Diagnostic Interview-Revised (ADI-R), did not demonstrate the same accuracy in this sample as they have in the general population. Improved screening and diagnostic assessments for more severely impaired adults with ASD, especially those that discriminate ASD from other psychiatric disorders, may have important implications for their treatment and supports.  The results of this study will aid in efforts to determine the prevalence of ASD among institutionalized adults, increase understanding of the prevalence of ASD in adults, and guide policy and practice regarding diagnostic practices and service delivery to adults with ASD.