The amnestic disorders are a group of disorders that involve loss of memories previously established, loss of the ability to create new memories, or loss of the ability to learn new information. As defined by the mental health professional's handbook, the Diagnostic and Statistical Manual of Mental Disorders , fourth edition, text revision (2000), also known as DSM-IV-TR , the amnestic disorders result from two basic causes: general medical conditions that produce memory disturbances; and exposure to a chemical (drug of abuse, medication, or environmental toxin). An amnestic disorder whose cause cannot be definitely established may be given the diagnosis of amnestic disorder not otherwise specified.
The amnestic disorders are characterized by problems with memory function. There is a range of symptoms associated with the amnestic disorders, as well as differences in the severity of symptoms. Some people experience difficulty recalling events that happened or facts that they learned before the onset of the amnestic disorder. This type of
amnesia is called retrograde amnesia. Other people experience the inability to learn new facts or retain new memories, which is called anterograde amnesia. People with amnestic disorders do not usually forget all of their personal history and their identity, although memory loss of this degree of severity occurs in rare instances in patients with dissociative disorders.
Causes and symptoms
In general, amnestic disorders are caused by structural or chemical damage to parts of the brain . Problems remembering previously learned information vary widely according to the location and the severity of brain damage. The ability to learn and remember new information, however, is always affected in an amnestic disorder.
Amnestic disorder due to a general medical condition can be caused by head trauma, tumors, stroke , or cerebrovascular disease (disease affecting the blood vessels in the brain). Substance-induced amnestic disorder can be caused by alcoholism, long-term heavy drug use, or exposure to such toxins as lead, mercury, carbon monoxide, and certain insecticides. In cases of amnestic disorder caused by alcoholism, it is thought that the root of the disorder is a vitamin deficiency that is commonly associated with alcoholism, known as Korsakoff's syndrome. The causes of transient global amnesia, or TGA, are unclear.
In addition to problems with information recall and the formation of new memories, people with amnestic disorders are often disoriented with respect to time and space, which means that they are unable to tell an examiner where they are or what day of the week it is. Most patients with amnestic disorders lack insight into their loss of memory, which means that they will deny that there is anything wrong with their memory in spite of evidence to the contrary. Others will admit that they have a memory problem but have no apparent emotional reaction to their condition. Some persons with amnestic disorders undergo a personality change; they may appear apathetic or bland, as if the distinctive features of their personality have been washed out of them.
Some people experiencing amnestic disorders confabulate, which means that they fill in memory gaps with false information that they believe to be true. Confabulation should not be confused with intentional lying. It is much more common in patients with temporary amnestic disorders than it is in people with long-term amnestic disorders.
Transient global amnesia (TGA) is characterized by episodes during which the patient is unable to create new memories or learn new information, and sometimes is unable to recall past memories. The episodes occur suddenly and are generally short. Patients with TGA often appear confused or bewildered.
The overall incidence of the amnestic disorders is difficult to estimate. Amnestic disorders related to head injuries may affect people in any age group. Alcohol-induced amnestic disorder is most common in people over the age of 40 with histories of prolonged heavy alcohol use. Amnestic disorders resulting from the abuse of drugs other than alcohol are most common in people between the ages of 20 and 40. Transient global amnesia usually appears in people over 50. Only 3% of people who experience transient global amnesia have symptoms that recur within a year.
Amnestic disorders may be self-reported, if the patient has retained insight into his or her memory problems. More often, however, the disorder is diagnosed because a friend, relative, employer, or acquaintance of the patient has become concerned about the memory loss or recognizes that the patient is confabulating, and takes the patient to a doctor for evaluation. Patients who are disoriented, or whose amnesia is associated with head trauma or substance abuse, may be taken to a hospital emergency room.
The doctor will first examine the patient for signs or symptoms of traumatic injury, substance abuse, or a general medical condition. He or she may order imaging studies to identify specific areas of brain injury, or laboratory tests of blood and urine samples to determine exposure to environmental toxins or recent consumption of alcohol or drugs of abuse. If general medical conditions and substance abuse are ruled out, the doctor may administer a brief test of the patient's cognitive status, such as the mini-mental state examination or MMSE. The MMSE is often used to evaluate a patient for dementia , which is characterized by several disturbances in cognitive functioning (speech problems, problems in recognizing a person's face, etc.) that are not present in amnestic disorders. The doctor may also test the patient's ability to repeat a string of numbers (the so called digit span test) in order to rule out delirium . Patients with an amnestic disorder can usually pay attention well enough to repeat a sequence of numbers where as patients with delirium have difficulty focusing or shifting their attention. In some cases the patient may also be examined by a neurologist (a doctor who specializes in disorders of the central nervous system)
If there is no evidence of a medical condition or substance use that would explain the patient's memory problems, the doctor may test the patient's memory several times in order to rule out malingering or a factitious disorder . Patients who are faking the symptoms of an amnestic disorder will usually give inconsistent answers to memory tests if they are tested more than once.
DSM-IV-TR specifies three general categories of amnestic disorders. These are: amnestic disorder due to a general medical condition, substance-induced persisting amnestic disorder, and amnestic disorder not otherwise specified. The basic criterion for diagnosing an amnestic disorder is the development of problems remembering information or events that the patient previously knew, or inability to learn new information or remember new events. In addition, the memory disturbance must be sufficiently severe to affect the patient's social and occupational functioning, and to represent a noticeable decline from the patient's previous level of functioning. DSM-IV-TR also specifies that the memory problems cannot occur only during delirium, dementia, substance use or withdrawal.
There are no treatments that have been proved effective in most cases of amnestic disorder, as of 2002. Many patients recover slowly over time, and sometimes recover memories that were formed before the onset of the amnestic disorder. Patients generally recover from transient global amnesia without treatment. In people judged to have the signs that often lead to alcohol-induced persisting amnestic disorder, treatment with thiamin may stop the disorder from developing.
Amnestic disorders caused by alcoholism do not generally improve significantly over time, although in a small number of cases the patient's condition improves completely. In many cases the symptoms are severe, and in some cases warrant long-term care for the patient to make sure his or her daily needs are met. Other substance induced amnestic disorders have a variable rate of recovery, although in many cases full recovery does eventually occur. Transient global amnesia usually resolves fully.
Amnestic disorders resulting from trauma are not generally considered preventable. Avoiding exposure to environmental toxins, refraining from abuse of alcohol or other substances, and maintaining a balanced diet may help to prevent some forms of amnestic disorders.
See also Dissociative amnesia
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American Academy of Child and Adolescent Psychiatry. P. O. Box 96106, Washington, D.C. 20090. (800) 333-7636. <www.aacap.org> .
Tish Davidson, A.M.