specific lesions or related to single neurotransmitter abnormalities.
The most commonly neglected component of the biopsychosocial model is the role played by socio-cultural forces in dual diagnosis. Over the past three centuries, attitudes and values about individuals with IDD changed dramatically. These changes impact the social risk factors on the epidemiology, availability and types of habilitation and treatment services for those with IDD and mental disorders. In industrialized societies, urbanization and changing modes of living and working placed new occupational and educational demands that changed the niche occupied by individuals with ID. For example, many individuals with IDD now live in a society where there are fewer less technologically demanding jobs (requiring basic skill sets) and these jobs are often subject to increasing competition. These social changes are complicated by smaller families, greater geographic mobility and the problem of isolation from traditional sources of family support. Today families rely upon “professional services” to fill this void (8).
These social and cultural changes are redefining our sense of community. Historically, attitudes such as relative pessimism by medical providers about a lack of effective interventions and prognosis; marginalization and socio-economic segregation of individuals and their families; and lack of community-based resources contributed to out-of-home residential placement. Governmental actions focused mainly on developing programs that eventually became large custodial institutions (25). As an outgrowth of the Civil and Human Rights movement and numerous lawsuits, there is a shift to community care, inclusion, freedom of choice, active treatment and protection from various forms of restraint. But these changes are quite vulnerable to economic downturns; legislative battles ensue over cost-effectiveness instead of treatment efficacy. Unfortunately, there has been a resurgence of ambivalence about placing group homes in residential neighborhoods as well as availability and adequate resources for staff and educators. Finally, limitations on funding and access to an integrated system of comprehensive health and mental health care (26) are present in many states. The care of high service users such as those with dual diagnosis is especially vulnerable to these socio-political forces (8, 27–29). This unfortunate scenario may underlie the recent trends toward increasing use of psychotropic drugs (30, 31).
It is also important to recognize a selection bias inherent in most mental health referrals. Since referrals arise due to disruptive, destructive, self-injurious behaviors or irritable/aggressive behaviors we must maintain a high index of suspicion for unrecognized psychiatric or medical/neurological disorders. Sorting out these generic referrals is the function of differential diagnosis. The following steps are useful in this process:
Data collection and decision making: Collect medical, psychiatric and developmental histories—both indirect reports and direct observations—and data from available rating scales. Convert this information into a timeline to create a visual representation of behavioral or symptom change through time. Converting behavioral information into a graphic format permits the clinician to track both behavioral data but also to integrate syndrome change (e.g. bipolar disorder); severity and intensity measures; and findings from serial mental status and rating scales. The Assessment of Dual Diagnosis (ADD) (32), the Emotional Problems Scale: Behavior Ratings Scale (EPS-R) (33) and The Diagnostic Assessment for the Severely Handicapped-II (34) are informant–based rating scales that cross-walk with the DSM-IV TR. The ADD and EPS-R were developed for patients with mild to moderate IDD whereas the DASH-II was developed for patients with SPIDD. Treatment response can also fit into this scheme (15).
Management of medical/neurological and laboratory data: Include and integrate relevant baseline medical studies, available information on genetic an