Chapter 027. Aphasia, Memory Loss, and Other Focal Cerebral Disorders (Part 12)

The patient with an amnestic state is almost always disoriented, especially to time. Accurate temporal orientation and accurate knowledge of current news rule out a major amnestic state. The anterograde component of an amnestic state can be tested with a list of four to five words read aloud by the examiner up to five times or until the patient can immediately repeat the entire list without intervening delay. In the next phase of testing, the patient is allowed to concentrate on the words and to rehearse them internally for 1 min before being asked to recall them. Accurate performance...
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Chapter 027. Aphasia, Memory Loss, and Other Focal Cerebral Disorders (Part 12) Chapter 027. Aphasia, Memory Loss, and Other Focal Cerebral Disorders (Part 12) The patient with an amnestic state is almost always disoriented, especiallyto time. Accurate temporal orientation and accurate knowledge of current newsrule out a major amnestic state. The anterograde component of an amnestic statecan be tested with a list of four to five words read aloud by the examiner up to fivetimes or until the patient can immediately repeat the entire list without interveningdelay. In the next phase of testing, the patient is allowed to concentrate on thewords and to rehearse them internally for 1 min before being asked to recall them.Accurate performance in this phase indicates that the patient is motivated andsufficiently attentive to hold the words online for at least 1 min. The final phase ofthe testing involves a retention period of 5–10 min, during which the patient isengaged in other tasks. Adequate recall at the end of this interval requires offlinestorage, retention, and retrieval. Amnestic patients fail this phase of the task andmay even forget that they were given a list of words to remember. Accuraterecognition of the words by multiple choice in a patient who cannot recall themindicates a less severe memory disturbance that affects mostly the retrieval stageof memory. The retrograde component of an amnesia can be assessed withquestions related to autobiographical or historic events. The anterogradecomponent of amnestic states is usually much more prominent than the retrogradecomponent. In rare instances, usually associated with temporal lobe epilepsy orbenzodiazepine intake, the retrograde component may dominate. The assessment of memory can be quite challenging. Bedside evaluationsmay only detect the most severe impairments. Less severe memory impairments,as in the case of patients with temporal lobe epilepsy, mild head injury, or earlydementia, require quantitative evaluations by neuropsychologists. Confusionalstates caused by toxic-metabolic encephalopathies and some types of frontal lobedamage interfere with attentional capacity and lead to secondary memoryimpairments, even in the absence of any limbic lesions. This sort of memoryimpairment can be differentiated from the amnestic state by the presence ofadditional impairments in the attention-related tasks described below in the sectionon the frontal lobes. Many neurologic diseases can give rise to an amnestic state. These includetumors (of the sphenoid wing, posterior corpus callosum, thalamus, or medialtemporal lobe), infarctions (in the territories of the anterior or posterior cerebralarteries), head trauma, herpes simplex encephalitis, Wernicke-Korsakoffencephalopathy, paraneoplastic limbic encephalitis, and degenerative dementiassuch as Alzheimers or Picks disease. The one common denominator of all thesediseases is that they lead to the bilateral lesions within one or more components inthe limbic network, most commonly the hippocampus, entorhinal cortex, themammillary bodies of the hypothalamus, and the limbic thalamus. Occasionally,unilateral left-sided lesions can give rise to an amnestic state, but the memorydisorder tends to be transient. Depending on the nature and distribution of theunderlying neurologic disease, the patient may also have visual field deficits, eyemovement limitations, or cerebellar findings. Transient global amnesia is a distinctive syndrome usually seen in latemiddle age. Patients become acutely disoriented and repeatedly ask who they are,where they are, what they are doing. The spell is characterized by anterograde amnesia (inability to retain newinformation) and a retrograde amnesia for relatively recent events that occurredbefore the onset. The syndrome usually resolves within 24–48 h and is followed by thefilling-in of the period affected by the retrograde amnesia, although there ispersistent loss of memory for the events that occurred during the ictus.Recurrences are noted in ~20% of patients. Migraine, temporal lobe seizures, and transient ischemic events in theposterior cerebral territory have been postulated as causes of transient globalamnesia. The absence of associated neurologic findings may occasionally lead tothe incorrect diagnosis of a psychiatric disorder. The Prefrontal Network for Attention and Behavior Approximately one-third of all the cerebral cortex in the human brain islocated in the frontal lobes. The frontal lobes can be subdivided into motor-premotor, dorsolateral prefrontal, medial prefrontal, and orbitofrontal components. The terms frontal lobe syndrome and prefrontal cortex refer only to the lastthree of t ...