It begins with delirium, followed by the syndromes of major NCD, mild NCD, and their etiological subtypes. Neurocognitive disorders including delirium, mild cognitive impairment and dementia are characterized by decline from a previously attained level of cognitive functioning. These disorders have diverse clinical characteristics and aetiologies, with Alzheimer disease, cerebrovascular disease, Lewy body disease, frontotemporal degeneration, traumatic brain injury, infections, and alcohol abuse representing common causes.
Major neurocognitive disorder was previously known as dementia and the primary feature of all neurocognitive disorders (NCDs) is an acquired cognitive decline in one or more cognitive domains. The cognitive decline must not just be a sense of a loss of cognitive abilities, but observable by others — as well as tested by a cognitive assessment (such as a neuropsychological test battery).