Delirium and dementia are the most common causes of lack of mental functioning according to the Merck Manual. People with either or both of these disorders are unable to increase, retain, and use knowledge in the normal fashion. Delirium and dementia may occur together, but their medical definitions are quite different.
Delirium starts quite suddenly, causes changes in mental functioning, and is often reversible according to the medical definition. Delirium affects mainly attention. People with delirium are often disoriented, unable to think clearly, and may be hyper one minute and in a sleep-like state the next. There are many causes of delirium. It may occur at any age. It is more common in older people because of changes in the brain that occur with age. Delirium affects 15 percent to 50 percent of hospitalized people who are 70 or older, according to the Merck Manual. It is common among nursing home residents.
A person with dementia gets worse over time. The disease slowly progresses and is most often irreversible. Dementia usually affects a person's short-term memory first. The other problems that a person with dementia may have include difficulty with language, planning ahead and judgment, simple mathematical calculations, and movement according to the medical definition. Age is a common risk factor for dementia. As the disease progresses, mental functions....read all of Medical Definition of Delirium & Dementia