Delirium is characterized by a sudden onset, fluctuating course, a short duration (often lasting from hours to weeks), and is primarily related to a somatic (or medical) disturbance. In comparison, dementia has typically a long, slow onset (except in the cases of a stroke or trauma), slow decline of mental functioning, as well as a longer trajectory (from months to years).Some mental illnesses, including depression and psychosis, may produce symptoms that must be differentiated from both delirium and dementia. These are differently diagnosed as pseudodementias, and any dementia evaluation needs to include a depression screening such as the Neuropsychiatric Inventory or the Geriatric Depression Scale. Physicians used to think that people with memory complaints had depression and not dementia (because they thought that those with dementia are generally unaware of their memory problems). However, researchers have realized that many older people with memory complaints in fact have mild cognitive impairment the earliest stage of dementia. Depression should always remain high on the list of possibilities, however, for an elderly person with memory trouble. Changes in thinking, hearing and vision are associated with normal ageing and can cause problems when diagnosing dementia due to the similarities. Given the challenging nature of predicting the onset of dementia and making a dementia diagnosis clinical decision making aids underpinned by machine learning and artificial intelligence have the potential to enhance clinical practice. Cognitive testing
Various brief cognitive tests (5–15 minutes) have reasonable reliability to screen for dementia, but may be affected by factors such as age, education and ethnicity.
In 1907, Bavarian psychiatrist Alois Alzheimer was the first to identify and describe the characteristics of progressive dementia in the brain of 51-year-old Auguste Deter. Deter had begun to behave uncharacteristically, including accusing her husband of adultery, neglecting household chores, exhibiting difficulties writing and engaging in conversations, heightened insomnia, and loss of directional sense. At one point, Deter was reported to have "dragged a bed sheet outside, wandered around wildly, and cried for hours at midnight." Alzheimer began treating Deter when she entered a Frankfurt mental hospital on November 25, 1901. During her ongoing treatment, Deter and her husband struggled to afford the cost of the medical care, and Alzheimer agreed to continue her treatment in exchange for Deters medical records and donation of her brain upon death. Deter died on April 8, 1906, after succumbing to sepsis and pneumonia. Alzheimer conducted the brain biopsy using the Bielschowsky stain method, which was a new development at the time, and he observed senile plaques, neurofibrillary tangles, and atherosclerotic alteration. At the time, the consensus among medical doctors had been that senile plaques were generally found in older patients, and the occurrence of neurofibrillary tangles was an entirely new observation at the time. Alzheimer presented his findings at the 37th psychiatry conference of southwestern Germany in Tübingen on April 11, 1906; however, the information was poorly received by his peers.