Background: Despite widespread acceptance that depression can occur in adults with intellectual disability (ID), the difficulties encountered in its assessment and diagnosis have hampered the individual clinician, and meant that questions of prevalence, treatment choice and outcome remain problematic.
Methods: The present paper reviews the progress in this field since three reviews, all published in the mid-1990s, recommended further attention to three interlinked issues: diagnostic criteria, the symptoms of depression in this group and the lack of rating scales.
Results: Despite a further 11 published papers and other studies in progress, the method of diagnosis for people with severe and profound ID remains debatable, with some authors advocating adherence to standard criteria, others suggesting adding criteria to the standard ones and yet others believing that substitute criteria are called for. However, for those with mild to moderate ID, a consensus is emerging that standard diagnostic criteria are appropriate. There has been progress in examining some of the symptoms which might constitute depression in people with ID. New diagnostic criteria issued by the Royal College of Psychiatrists are to be welcomed. There is an assumption in much of the research that symptoms of behaviour commonly termed challenging or maladaptive must be atypical symptoms of depression, but none of the studies reviewed demonstrate this effectively. This is compounded by methodological flaws in the way that depressed samples are arrived at for further study. Although new rating scales have emerged, there is as yet no gold standard diagnostic tool for depression amongst people with ID.
Conclusion: It is suggested that, given these difficulties, the validity of the conceptual frameworks for depression is still in doubt. It remains the case that large-scale, collaborative, prospective studies are called for.