In the first post, I defined dementia as a nondescript umbrella term that is commonly used to refer to any acquired (not congenital) condition in which there is a progressive, often irreversible, decline in cognitive and functional abilities from a prior baseline. It affects one or more of the following cognitive abilities: memory and learning, complex attention, language skills, social cognition, perceptual-motor skills, and a broad category called executive dysfunction. I also emphasized in the introductory post that dementia is not solely diagnosed based on cognitive dysfunction; rather, diagnosis requires an impairment in the ability for independent living.
The topic for this post is the diagnostic process involved in a dementia work-up. Currently, clinical history remains the most critical diagnostic tool. Since individuals with dementia are often unaware of their deficits (called anosognosia) or defend against them, an interview with a family member(s) or other knowledgeable informants is indispensable to supplement the affected person’s account. The history should focus on the cognitive domains impacted, the severity of the impairment, and course of onset (gradual or sudden) and progression (steadily progressive, fluctuating, stepwise, etc.) of the deficits. An account of the day-to-day functional impairment (paying bills, cooking, cleaning, laundry, driving, self-care, etc.) is absolutely essential to the diagnosis. Many brief rating instruments are available that can assist in identifying and cataloguing the cognitive and functional deficits as we shall discuss in a future post.
Next, a comprehensive medical history should be obtained that captures relevant medical and neurological issues, and a family history of dementia which is especially important for young-onset (age < 65) cases. Common medical conditions that may manifest with cognitive symptoms include thyroid and other hormonal irregularities, nutritional deficiencies such as folate and vitamin B12, systemic or central nervous system infectious or inflammatory processes, tumors, toxins, head trauma, seizures, and substance or medication effects, to list a few. Young-onset dementia might suggest the need for genetic testing to identify certain known genetic defects associated with Alzheimer’s and other types of dementia. Finally, careful psychiatric history should be obtained since many psychiatric conditions are associated with cognitive deficits.
The physical and neurological exam may identify other clues to the underlying pathophysiology. For example, individuals with neurological conditions may manifest focal deficits such as numbness, weakness, tremor, rigidity, slowed movements, recurrent falls, swallowing and speech deficits, or visual field cuts. Those with cardiovascular risk factors may display irregular heart rhythm, blood pressure abnormalities, carotid bruits, and much else. Some dementia conditions produce specific physical findings such as the golden-brown eye discoloration (Kayser-Fleischer rings) of Wilson’s disease. Such focalizing findings on the physical exam often dictate further laboratory, neurophysiological, and neuroimaging work-up.
Much of the laboratory testing for dementia attempts to identify reversible conditions that produce cognitive deficits. Examples include thyroid function, nutritional deficiencies, and infectious or inflammatory processes, to list a few. In some situations, measurement of cerebrospinal fluid (fluid that surrounds and cushions the brain and spinal cord) beta-amyloid and tau levels (protein abnormalities) may increase or decrease the certainty of an Alzheimer’s diagnosis.
While a brain imaging study such as a CT or MRI is often helpful in the overall diagnostic process, a neuroimaging study is not a prerequisite for a dementia diagnosis. Structural neuroimaging studies which provide a static picture of the brain can often identify specific patterns of brain shrinkage and other types of damage (for example, strokes) that guide the treatment process. Likewise, functional neuroimaging studies that measure metabolic activity in various brain regions also provide pictures that may be more characteristic of one type of dementia than another. More recently, chemical compounds have been developed that can bind to the beta-amyloid plaques present in the brains of individuals with neurodegenerative conditions to assist in the differential diagnosis of dementia. I will discuss these patterns in future posts when we discuss specific types of dementias.
Finally, when confronted with a highly unusual or atypical presentation, medical specialists such as neurologists, cardiologist, medical geneticists, psychiatrists, and neuropsychologists may need to be involved. The key point should be that one physician (geriatrician, geriatric psychiatrist, neurologist, etc.) coordinates all the care and synthesizes the history and workups to best educate the affected individual and their family members.
In the next post, I will focus specifically on the phenomenology and course of Alzheimer’s disease.