After studying this chapter, the student should be able to:
Define the terms dementia and mild cognitive impairment (MCI).
Understand how patients are screened and diagnosed by history, physical exam, and standardized tests.
Identify different types of dementia based on clinical presentations, neuropathology, and pathogenesis.
Explain pharmacologic and nonpharmacologic management of cognitive disorders.
One of the most striking demographic trends over the past century has been a dramatic extension of life expectancy, which has almost doubled from 44 years in 1890 to >80 years today. An unfortunate accompaniment of this change is an increase in age-related cognitive change, perhaps the most common and feared result of aging. Age-related cognitive change includes both “normal” cognitive aging and several neurodegenerative diseases causing dementia.
Among the neurodegenerative diseases, Alzheimer disease (AD) is the most common, affecting >5 million people in the United States. Interestingly, the incidence (rate of new cases per unit of population) of dementia seems to be declining worldwide, with improvement in control of vascular risk factors and other public health improvements. However, the prevalence (overall number of cases) of dementia is still growing at an alarming rate. The risk of developing dementia due to AD doubles every 5 years after age 65 years, and with the growth of the aged population, AD prevalence is expected to continue increasing dramatically.
One of the reasons it is important to define which cognitive domains are involved in a patient’s cognitive decline is the fact that each domain has a particular anatomy. Thus, identifying an impaired domain is the primary mode of localization in behavioral neurology. Episodic memory localizes to the medial temporal lobe, including the hippocampus (Chapter 20). Language is generally localized to the left hemisphere and can be more precisely localized based on the type of aphasia (Chapter 21). Visuospatial function is generally localized more to the right hemisphere and occipital, and executive function is primarily frontal.
The history is the most important part of the workup in diagnosing cognitive disorders. A collateral informant is usually helpful because the patient’s deficits may prohibit the patient from providing a reliable history. An important goal is to identify the initial symptoms, which enables inferring the initial cognitive domain involved and in turn defining the initial neuroanatomy, a key factor in differential diagnosis. Later in the course of neurodegenerative diseases, multiple brain regions invariably become involved, and thus multiple domains are affected. Elucidating the initial symptoms can suggest where in the brain the pathologic process might have started. It is important to remember that patients may use the term “memory” to refer to other cognitive domains. For example, “I can’t remember words” is likely to reflect language impairment, and “I forget ...