The amnestic disorders are a broad category that includes a variety of diseases and conditions that present with amnesia or loss of memory. Three types exist: (1) amnestic disorder due to a general medical condition (such as head trauma), (2) substance-induced persisting amnestic disorder (such as due to carbon monoxide poisoning or chronic alcohol consumption), and (3) amnestic disorder not otherwise specified (NOS) for cases in which the etiology is unclear. There are two modifiers for this condition: (1) transient, for conditions lasting less than 1 month, and (2) chronic, for conditions lasting more than 1 month.

Most common form is caused by thiamine deficiency associated with alcohol dependence. May also result from head trauma, surgery, hypoxia, infarction, and herpes simplex encephalitis. Typically, any process that damages certain diencephalic and medial temporal structures (e.g., mammillary bodies, fornix, and hippocampus) can cause the disorder. See Table 8-1.

The essential feature is the acquired impaired ability to learn and recall new information coupled with the inability to recall past events. Impaired recent, short-term memory and long-term memory is caused by systemic medical or primary cerebral disease. Patient is normal in other areas of cognition.

Amnestic disorders are diagnosed according to their etiology: amnestic disorder resulting from a general medical condition, substance-induced persisting amnestic disorder, and amnestic disorder NOS.