Delirium is characterized by a sudden onset of symptoms. Patients often have multiple cognitive deficits such as an inability to maintain attention to external stimuli and/or perseveration, disorganized thinking (e.g., rambling, irrelevant, or incoherent speech), and reduced levels of consciousness (e.g., perhaps having difficulty staying awake during the examination), and they may have disturbed sleep patterns, psychomotor agitation or retardation, disorientation, and/or memory impairment. Symptoms usually develop over a short period of time (spontaneously in many cases), and they fluctuate throughout the course of the day. There is either evidence of a specific organic factor (e.g., intracranial trauma, the effects of drugs, nonendocrine organ disease, endocrine dysfunction, a deficiency disease such as a thiamin deficiency, systemic infection, electrolyte imbalance, or a postoperative state) or in the absence of a known organic factor, one or more can normally be presumed.
In contrast to delirium, dementia occurs most often in old age and in most cases it is caused by a primary, permanent, degenerative process affecting an individual's orientation, memory, perception, intellectual function, reasoning, and judgment. Frequently, individuals with dementia have poor impulse control and lability of mood that are not characteristic of the individual's premorbid personality. Early signs of dementia include difficulties in mental performance (e.g., memory), fatigue, and an inability to perform new or complex tasks. As the disorder progresses, everyday and familiar tasks become difficult to perform successfully, and taking care of basic needs eventually becomes impossible. Language may or may not be affected, and affected individuals often will attempt to compensate for deficits by joking, changing the subject, or by diverting the interviewer's attention.
Amnestic disorders are also characterized by an impairment of memory, but in contrast to delirium and dementia, amnestic disorders are not characterized by global deficits in intellectual and cognitive functioning. Short-term memory and recent memory are affected, and the individual usually lacks insight into these memory deficits and will try to minimize, deny, or rationalize them. Like delirium (and in contrast to dementia) the onset of amnestic disorders is usually sudden. If symptoms are of a global nature, therefore, and/or of gradual onset, an underlying dementia or possibly a brain tumor should be suspected. Amnestic disorders are not well known, however they are commonly seen among individuals with alcohol use disorders, and occasionally amnestic disorders will follow trauma such as a head injury or electroconvulsive therapy.
Several medical conditions can cause psychiatric symptoms, but for a diagnosis of Mental Disorder Due to a General Medical Condition to be made, the symptoms must be assumed to be caused by the direct physiological effects of a general medical condition. Examples of disorders falling into this category include Mood Disorder Due to a General Medical Condition (e.g., HIV or AIDS), Anxiety Disorder Due to a General Medical Condition (e.g., cancer), Catatonic Disorder Due to a General Medical Condition (e.g., head trauma, encephalitis, cerebrovascular disease, metabolic conditions), Psychotic Disorder Due to a Medical Condition (e.g., an electrolyte imbalance), and Personality Change Due to a General Medical Condition (e.g., head trauma). It is important to note than when choosing this type of diagnosis there must be evidence from the individual's history, physical examination, or laboratory tests that the mental disturbance is a direct physiological consequence of a general medical condition, that the mental disturbance cannot be better explained by another mental disorder, and that the mental symptoms cannot occur solely in the course of delirium—unless a diagnosis of Delirium due to a General Medical Condition is appropriate. It is important to consider whether the onset of the medical condition and mental symptoms occur closely in time (they usually, but not always, do, whether the signs of the mental disorder are typical or atypical (they will often be atypical), and whether the known medical condition usually produces symptoms similar to those that the individual is experiencing.
HIV disorder is often accompanied by psychological changes that will vary with the stage of illness. Whereas depression and anxiety may occur early on, more pervasive changes such as personality changes and dementia may occur later. A diagnosis of an HIV-related psychiatric disorder is made when an individual qualifies for a psychiatric diagnosis and it is believed that the disorder is a direct result of having HIV illness. In some cases it can be shown that the disorder is the direct physiological consequence of HIV infection, such as in the case of HIV-related dementia. The correct diagnosis in this case would be Dementia Due to a General Medical Condition, and HIV Disease or similar would be noted as the cause. In other cases mental symptoms may be due to a reaction to having HIV Disease, such as depression or anxiety, but not directly due to any HIV-related physiological changes. The correct diagnosis in this case would be the appropriate psychiatric disorder for which the diagnostic criteria are met, and HIV Disease would be noted as a stressor or otherwise contributing factor.