Amnesia refers to the loss of memory. Anterograde amnesia, in particular, refers to the ability to lay down new memories. Persons with anterograde amnesia may not remember a conversation that occurred just minutes ago but are likely to remember basic facts ("who is the president of the United States?") and childhood events. The condition may be very temporary, for example, following a concussion, or it may be permanent, as in Korsakoff's Syndrome (neuronal loss due to severe thiamine deficiency). Anterograde amnesia has a number of potential causes, including acute alcohol intoxication ("blacking out"), prolonged alcoholism, head trauma, stroke, or the use of certain benzodiazepines (such as Ativan or Rohypnol) or sleep-inducing drugs (such as Ambien).
A much more common form of memory loss is dementia, which is distinct from anterograde amnesia. Persons with amnesia, although they may have severe deficiencies of memory, are otherwise unaffected. Their intelligence, judgment, awareness, and personality are typically unchanged. In dementia, memory difficulties are frequently accompanied by other cognitive impairments that impact the patient's ability to function in day-to-day life, such as difficulty with words, problems with movement, and personality changes such as agitation.
Persons with anterograde amnesia may not perceive any symptoms, or they may be profoundly confused and disoriented. The diagnosis is typically made when a friend or family member notices memory issues and brings the amnestic individual to a doctor. The doctor is likely to perform a general assessment of memory and cognitive ability, such as the Mini Mental State Examination, and to interview the patient to understand the extent of the symptoms and to begin to rule out potential causes. Family history of dementia, or history of drug use, for example, may help the doctor make an appropriate diagnosis. Doctors may perform additional tests, including brain scans (such as CT or MRI) to rule out tumors, blood tests in case of thiamine deficiency, or psychiatric tests to evaluate the potential contribution of psychological conditions such as depression.
The Mayo Clinic has a helpful explanation of the disorder and its treatment.