Cognitive Disorders 697
What distinguishes amnestic disorder from delirium, which may involve mem-ory problems? With amnestic disorder, the memory problem is the sole cognitive
impairment—there is no signifi cant change in consciousness or attention or other
mental processes—as was the case for Ms. A in Case 15.3. Impaired memory is
also the key symptom of dissociative amnesia (see Chapter 8), but with that disor-
der, the impairment is generally limited to particular types of memories—traumatic
or otherwise stressful ones. Moreover, amnestic disorder is diagnosed only when
there is strong reason to believe that the memory problems are related to a medical
condition or substance use; in contrast, the impaired memory of dissociative amne-
sia is thought to be caused by psychological trauma. And, although it is normal to
have some memory problems with advanced age, a diagnosis of amnestic disorder
indicates memory problems that are signifi cantly more severe than those due sim-
ply to aging.
Is amnestic disorder an appropriate diagnosis for Mrs. B.’s problems? No;she has other cognitive problems—revealed by her poor performance on the Trail
Making Test.
Understanding Amnestic Disorder
Amnestic disorder is caused exclusively by one of two types of neurological factors:
substance use or a medical condition. However, the disorder typically has different
courses of development in the two cases: When the disorder is caused by chronic sub-
stance abuse or exposure to a toxin, memory usually becomes impaired gradually.
(One medical condition that gradually leads to amnestic disorder is chronic malnu-
trition.) In contrast, when amnestic disorder is caused by stroke or trauma to the
head, memory becomes impaired rapidly. Let’s consider the two types of causes in
more detail.
Substance-Induced Persisting Amnestic Disorder
When substance use causes the memory impairment and the amnesia lasts signifi -
cantly longer than the period of intoxication or withdrawal, the disorder falls un-
der the DSM-IV-TR diagnosis of substance-induced persisting amnestic disorder. To
make this diagnosis, there must be evidence from the individual’s history, a physical
examination, or laboratory tests that the impaired memory was caused by substance
use, exposure to certain toxins, or the effect of a medication.
Typically, people with this disorder have, or have had, substance dependence.Alcohol is the most common substance that leads to amnestic disorder; in DSM-IV-
TR it is referred to as alcohol-induced persisting amnestic disorder. Alcohol reduces
the absorption of the vitamin thiaminefrom food; thiamine is found in nuts, bread,
and some fruits, vegetables, and meats (Hochhalter et al., 2001). Severe thiamine
defi ciency can lead to signifi cant memory problems, specifi cally the amnestic dis-
order called Korsakoff’s syndrome. Memory symptoms often emerge after age 40,
usually abruptly, although subtle memory problems are often evident earlier. Un-
fortunately, the symptoms are likely to remain stable or diminish only somewhat
over time, even with sustained sobriety (Kapur & Graham, 2002; Victor, Adams, &
Collins, 1989).
Amnestic disorder can also be caused by environmental toxins such as lead,mercury, and carbon monoxide. In addition, relatively high doses and prolonged
intake of a barbiturate (such as Seconal) or a benzodiazepine (such as Valium; see
Chapter 9) may cause amnestic disorder. Amnestic disorder caused by such sub-
stances has a better prognosis than does that caused by alcohol. Once the individual
tapers off the use of the drug, the memory problems usually clear up.
Amnestic Disorder Due to a General Medical Condition
A variety of medical conditions can lead to amnestic disorder (O’Conner &
Lafl eche, 2006) by damaging brain areas involved in memory: the hippocampus,