Cognitive disorders are mental conditions that cause patients to have difficulty thinking. Although symptoms of these disorders vary, they are generally marked by impaired awareness, perception, reasoning, memory and judgment.

Cognition involves the mental processing of information. Memory and thought combine to store, retrieve and manipulate this information. When something goes wrong with this process, a cognitive disorder may result.

There are four major categories of cognitive disorders:

• Delirium. A change in consciousness that develops over a short period of time, typically a few hours to days. Patients find it difficult to pay attention or to think clearly and have reduced awareness of their environment.
  
  
• Dementia. A progressive deterioration of brain function that is marked by impairment of memory, confusion and inability to concentrate.
  
  
• Amnestic disorder (amnesia). Involves a significant loss of the memory, although there is no loss of other cognitive functions as there is in dementia.
  
  
• Cognitive disorder, not otherwise specified (NOS). Includes cognitive impairment and is presumed to be due to a general medical condition or substance use and does not fit into the other categories.

A wide variety of factors can lead to cognitive disorders, including general medical conditions, brain infections and head injury. Symptoms experienced by patients vary depending on the nature of the disorder that is present, but may include rapid shifting of consciousness, confusion and impaired memory.

Cognitive disorders are typically diagnosed following physical and neurological examinations. Imaging tests, blood tests and other tests (e.g., liver function tests, thyroid tests) may also be performed.

Treatment options differ depending on which condition is present. Though delirium can usually be treated effectively by addressing the underlying condition, the prognosis may be less optimistic for patients with dementia or amnesia.