CLINICAL HANDBOOK OF SCHIZOPHRENIA

CHAPTER 42INTELLECTUAL DISABILITYAND OTHERNEUROPSYCHIATRIC POPULATIONSRICHARD B. FERRELLTHOMAS W. McALLISTERConditions or disorders that alter the motor, sensory, or mental functions of the centralnervous system (CNS) may also alter the likelihood of CNS-based disorders or illnesses.These conditions or disorders may also change the symptomatic presentation of psychiatricillnesses, such as schizophrenia. They may also affect response to psychopharmacological,psychotherapeutic, and behavioral treatments. CNS disorders that result in intellectualdisability (ID) are a category of such conditions. We think that these ideas areimportant to the proper understanding and treatment of persons with schizophrenia whoalso have ID or other neuropsychiatric illnesses. Conditions such as Alzheimer’s disease,Parkinson’s disease, Huntington’s disease, multiple sclerosis, epilepsy, cerebrovasculardisease, and traumatic brain injury are often associated with psychotic symptoms or maydirectly cause psychosis. In this chapter we use ID as a paradigm or example of a neuropsychiatricdisorder that can occur concomitantly with schizophrenia. ID is not, however,a single disease or even a disease-state, as are the disorders we named earlier. Its causesare often multiple, obscure, speculative, or unknown. Demonstration of anatomical pathologyor of CNS pathophysiology, if it exists, is frequently still beyond the reach of currentscience.Although some evidence points to the increased susceptibility to schizophrenia ofpersons with ID, it is possible that individuals with ID may also develop schizophrenic illnessfor reasons not related to ID. Our ignorance of the causes of both ID and schizophreniastill greatly exceeds our knowledge. Our purpose is to survey important neuropsychiatricissues and recent findings with respect to the evaluation and treatment ofschizophrenia in intellectually disabled people.437