Dementia is a general term referring to the gradual worsening of a person’s cognitive, behavioral and functional abilities, usually over multiple years. A specific dementia diagnosis can guide treatment and prognosis (the expected course of a disease). Dementia subtypes allow for more precise understanding than the global term but don’t convey as much information as a specific diagnosis.
Here are five subtypes of dementia:
The cortex is the gray matter, which contains brain cells. Alzheimer’s disease and Frontotemporal dementia are examples of cortical dementia. These dementias affect higher-order cognitive function, like memory and language, and behaviors, such as disinhibition (e.g., yelling in the middle of a theatrical performance). The nature of cognitive deficits and behavioral problems vary according to the type of dementia and by individual, especially early on in the disease course. For example, people with mild Alzheimer’s disease tend to have memory problems and few behavioral problems. In contrast, people in the first stages of the behavioral variant of Frontotemporal dementia may have significant disinhibition while their memory may be relatively well preserved.
This subtype affects the brainstem and related structures, which are often affected by strokes. Parkinson’s disease dementia is a classic example of subcortical dementia. Memory is not usually as impaired as it is in someone with Alzheimer’s disease. The brainstem controls basic functions such as heart rate and breathing and one’s “fight or flight” response. So, this subtype of dementia may be viewed as a dysfunction of “fight or flight,” affecting arousal, attention, mood and motivation. People with subcortical dementia may have prominent apathy and/or depression.
Others may be very disinhibited, irritable and agitated. Some people with subcortical dementia can even have a combination of symptoms like apathy and irritability.
White matter dementia
The tracts connecting brain cells are called white matter. Multiple Sclerosis and Normal Pressure Hydrocephalus (NPH) preferentially affect the white matter. Strokes commonly affect these tracts as well. Apathy, forgetfulness, inattention and depression are common features of white matter dementia.
The term Mixed Dementia is usually reserved for the specific combination of Alzheimer’s disease and Vascular dementia (dementia caused by strokes/damage to blood vessels in the brain).
A disease that affects white matter and gray matter, or cortical and subcortical regions, may cause a “combination” dementia and a mixture of symptoms, as the name implies. Examples of such illnesses include Traumatic Brain Injury, HIV and strokes/cerebrovascular disease.
The symptoms of these dementias vary by disease. Systemic causes of dementia include B12 Deficiency, thyroid dysfunction, neurosyphilis and Wilson’s disease. “Tertiary neurosyphilis” may occur decades after syphilis is contracted. Since these diseases can all be treated effectively when caught early, it is important for people with dementia to have a medical assessment, including laboratory tests. NPH can also be listed in this category and represents a key reason to obtain brain imaging when dementia is suspected.
Delays in medical attention can make a specific diagnosis more difficult, render treatment less effective and increase suffering of unknowing patients and families. Early medical attention can truly make a difference in the treatment of dementia, as well as in pinpointing a specific diagnosis.
When it comes to diagnosing illness, some physicians are “lumpers,” who prefer to group similar symptoms together to obtain a diagnosis. Other doctors are detail-oriented “splitters,” who focus on individual symptoms to distinguish one disease from another. Of course, the best diagnostician can balance pattern recognition with highlighting differences.
A good clinician aims for diagnostic specificity to optimize treatment and planning. For example, someone with cardiac disease is generally best served by knowing whether this is something like atrial fibrillation or a cardiomyopathy, an electrophysiological issue or a problem of cardiac muscles. In this example, cardiac disease is a general term. Atrial fibrillation and cardiomyopathy are specific diagnoses (and even more precision as to the root cause of these diagnoses is often possible). Electrophysiological and cardiomuscular dysfunction are subtypes of cardiac disease, lying somewhere between the general and specific. Such subtypes can improve our understanding of a disease, its course (prognosis) and its treatment.
By: Anne Lipton, M.D., Ph.D.
To listen to Dr. Lipton's presentation on dementia, Parkinson's, Multiple Sclerosis and Traumatic Brain Injury, click here.
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