Diagnosis of mental disorders in people with intellectual disabilities

Abstract

Introduction Classification of mental disorders in people with intellectual disabilities (ID) continues to be a very active field since the last edition of this book (Sturmey, 1999). This chapter reviews the importance and functions of classification as well as psychometric properties that any adequate classification system must have. It then goes on to review classification in relation to intellectual disabilities, mental health and classification of mental health issues in people with ID. The final section highlights the changes that have occurred and areas for future development. The importance and functions of classification Classification is often seen as a hallmark of science: atomic theory and the Linnaean system advanced their respective folk technologies into sciences. Yet, nineteenth-century Alienists were reluctant to classify madness beyond insanity and mental deficiency. As psychiatry strived towards scientific respectability, classification progressed vigorously, especially in the twentieth century. Kraepelin (Kihlstrom, 2002) developed taxonomy of insanity into 15 aetiological classes. In the end he had to admit that the effort was in vain, and that classification by course and prognosis was more promising. The precursors of the Diagnostic and Statistical Manual (DSM) implied aetiology, but were based on presenting symptoms, as putative causes could not be observed. Presenting symptoms continue to be cardinal features of DSM and the International Classification of Disease (ICD). Critics of the early DSM-I and II noted that they were both explicitly psychoanalytical in orientation and did not guide the diagnostician as to the specific symptoms and were hence unreliable.