Once a patient is found to have the syndrome of dementia, it is necessary to identify the etiology. Numerous illnesses can cause dementia as broadly defined (see Table 15.1). Differentiation of these illnesses is important because some of them are reversible and some can be arrested. It is also important to identify the diseases that are neither reversible nor arrestable (e.g., neurodegenerative diseases) because some disease-specific symptomatic and neuroprotective treatments are now available and are discussed below.
Evaluation of a demented patient should always begin with a good history and examination. Histories of cognitive, neuropsychiatry, and functional impairment can be elicited from the patient, his or her caregivers, and medical records. Knowledge of patterns and timing of impairment greatly aids in establishing an etiology. Thorough
TABLE 15.1. Some Representative Causes of the Dementia Syndrome
Reversible Dementia without Persisting Deficits
Hypoxia (e.g., from anemia, decreased cardiac output, lung disease) Electrolyte imbalance (e.g., hyponatremia) Hepatic insufficiency
Endocrine disease (e.g., hyperthyroidism, Addison's disease, Cushing's disease) Some intoxications (e.g., therapeutic drugs) Bi2 deficiency (e.g., of short duration)
Normal pressure hydrocephalus (e.g., of short duration)
Arrestable Dementia with Persisting Deficits
Vascular dementia Alcoholic dementia
Trauma (e.g., dementia pugilistica) Syphilis (i.e., general paresis)
Some intoxications (e.g., lead)
Bi2 deficiency (e.g., long-standing) Normal pressure hydrocephalus (e.g., long-standing) Postencephalitic dementia
Alzheimer's disease Frontotemporal dementias
Huntington's disease Parkinson's disease Diffuse Lewy body disease
Multiple sclerosis Creutzfeldt-Jakob disease
Human immunodeficiency virus dementia
Progressive supranuclear palsy Amyotrophic lateral sclerosis
Adapted from Wright and Cummings (1996).
cognitive, neurological, and general medical examinations give objective evidence of deficits and also greatly aid in diagnosis.
The history and examination should guide the choice of medical tests in patients with dementia. Medical testing can be helpful with (1) identification of any reversible or arrestable illnesses that may be causing or worsening the dementia, and (2) identification and staging of nonreversible/nonarrestable illnesses for the purpose of appropriate treatment selection.
Laboratory studies are mainly done to screen for reversible and arrestable causes of dementia. The AAN and the American Psychiatric Association (APA) have published dementia practice guidelines in which appropriate laboratory screening studies have been suggested (APA, 1997; Knopman et al., 2001b). Tests for uncommon causes of dementia such as heavy-metal intoxication are not recommended unless the patient's history or exam suggest that this should be done. Lumbar puncture (LP) for analysis of cerebrospinal fluid is likewise not routinely done but should be considered when indicated by the history or exam. Standard surface electroencephalography (EEG) is probably not useful as a screening tool in the evaluation of dementia but should be used in certain circumstances, for example, if the patient's history suggests seizures, or if the patient may have a disease with a characteristic EEG pattern such as CreutzfeldtJakob disease.
Structural neuroimaging using noncontrasted CT or MRI is a mainstay of the dementia evaluation. Structural imaging can reveal reversible and arrestable causes of dementia such as space-occupying lesions (hematomas, tumors, hydrocephalus, etc.). In patients with neurodegenerative diseases, structural imaging can sometimes reveal patterns of atrophy and other changes that can help with diagnosis. Functional neu-roimaging using SPECT or positron emission tomography (PET) scanning measures cerebral blood flow and cerebral metabolic rate, respectively, and can reveal patterns of dysfunction characteristic of certain illnesses.
A formal neuropsychological evaluation can be used to delineate a patient's cognitive deficits and quantify their severity. A profile of relatively preserved and relatively impaired functions can be essential in differential diagnosis, particularly in the more borderline or difficult cases or when cognitive deficits are subtle or complex. Neuropsy-chological findings are also useful in addressing immediate practical needs, selecting treatments, and monitoring the patient's progress over the long-term. Table 15.2 summarizes the recommended procedures for a dementia evaluation.
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