Gary S. Moak, M.D.

“What is the difference between Alzheimer’s and Dementia?”  Geriatric psychiatrists all over the world hear this question frequently.  It is the most common question, bar none, posed by patients or their family members, once they have begun to face the daunting challenge of dementia.  This article will answer this important, frequently asked question, and will help you begin to understand the diagnoses of dementia.

Simply put, dementia is a category of brain diseases, whereas Alzheimer’s disease is one specific type of dementia.  Think of automobiles as a general category and Ford as a specific brand.   More medically oriented analogies include arthritis, which includes familiar types such as rheumatoid arthritis and osteoarthritis, and chronic obstructive pulmonary disease, which includes the specific diseases emphysema, chronic asthma, and bronchiectasis.

Now that we have established that Alzheimer’s disease is a type of dementia, the obvious next question is “what, exactly, is dementia?”  Most people associate Alzheimer’s disease with forgetfulness, but it (and other dementias) is much more than a memory disorder. According to the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition, Text Revision (DSM-IV-TR), published by the American Psychiatric Association, dementia is defined as a disorder that causes the development of multiple cognitive deficits including memory impairment and either aphasia, apraxia, agnosia, or executive cognitive deficits (see definitions, below).  The impairment must be sufficiently severe to interfere with normal, day-to-day functioning (job, social life, taking care of oneself, hobbies and activities).  And it must represent a clear decline from a previous level of function.

It is important to appreciate that dementia is a medical condition defined purely in behavioral terms.  There is no medical test to determine the presence of dementia.  Patients often are under the misunderstanding that dementia is diagnosed with a computerized tomography (CT) scan or magnetic resonance imaging (MRI) scan.  Such scans, and other medical-type tests, help diagnose the type of dementia present, but the determination that dementia is present is based solely upon the presence of the characteristic mental symptoms.

Alzheimer’s disease is the most common single cause of dementia.  It accounts for about two thirds of cases.  Vascular dementia and Lewy body dementia are the next most common causes of dementia.   Some patients with dementia have both Alzheimer’s and vascular dementia, a condition known as mixed dementia.  Other dementias are much less common.  This group of less frequent dementias includes dementia associated with Parkinson’s disease, frontotemporal dementia, primary progressive aphasia, normal pressure hydrocephalus, progressive supranuclear palsy, and alcohol-induced dementia.  Other conditions such as multiple sclerosis, nutritional deficiencies, head injury, and cancer chemotherapy sometimes result in dementia.  All together, the family of dementias commonly is referred to as Alzheimer’s disease and related disorders.

All dementias occur as a result of disease processes that impair functioning of the brain.  The process by which this damage occurs is different for each disease entity, and this accounts for the differences in symptoms and clinical features.  For example, Alzheimer’s disease is a condition of progressive brain cell death caused by a degenerative process.   Memory and language impairment may dominate the early course, and patients usually seem quite normal physically.  In contrast, vascular dementia is caused by circulatory problems in the brain.  It may cause patchy or random patterns of mental symptoms, and physical manifestations of stroke or poor circulation elsewhere in the body may be present. In Parkinson’s disease, executive functions may be most impaired, and the characteristic tremor, slowness of movement, and facial appearance may be present.  In frontotemporal dementia, personality and behavior changes may be the most prominent early symptoms.

Many dementias, such as Alzheimer’s, are progressive, meaning that they get worse as time goes by.  Others may not progress.  For example, with scrupulous control of high blood pressure, diabetes, and elevated cholesterol, and attention to other stroke prevention measures, vascular dementia sometimes can be prevented from getting worse.   Normal pressure hydrocephalus can be arrested by neurosurgical placement of a shunt.

So if dementia represents a general term for a category of diseases for which there are various causes, why do doctors sometimes tell people they have dementia rather than giving them a specific diagnosis?   Perhaps the most common explanation is that often the diagnosis is uncertain.  The features of the dementias overlap considerably and there are few tests that definitively distinguish the various causes one from another.  Thus, despite a careful and thorough diagnostic evaluation, the exact diagnosis sometimes cannot be made (see What is a Proper Diagnostic Evaluation for Dementia in TOPICS IN GERIATRIC PSYCHIATRY).   The presence of dementia often can be determined with confidence, but the exact cause may be hard to identify.  Because of this, physicians who are not specialists in this field may feel it is more cautious not to make a specific diagnosis.   Even those primary care physicians who are adept at recognizing the presence of dementia may have a hard time keeping up with the subtle nuances that separate these complex illnesses.

Sometimes, a less definitive diagnosis may be offered for the comfort of the patient.   As familiarity with Alzheimer’s disease has increased, more and more older patients have started to dread it.   They fear their doctors’ use of the “A-word” as much as they fear hearing the “C-word (cancer).  Patients told that they have dementia often express relief that “at least it’s not Alzheimer’s!”  Healthcare providers sometimes take advantage of this to soften the blow and make the diagnosis easier to cope with.

Finally, one additional source of confusion between Alzheimer’s and dementia has to do with the branding, labeling, and marketing of specialized services for people with Alzheimer’s disease and related disorders.  You may have noticed that many nursing homes and assisted living facilities have “Alzheimer units”.  Such programs are usually not intended exclusively for people with Alzheimer’s disease.  Most of the time, they are meant for the broader group of people with Alzheimer’s disease and related disorders.  “Alzheimer’s” has, to some extent, become shorthand for “dementia”.  Think of the way that people use “Jello” to refer to gelatin desserts or “Kleenex” to mean “tissues”.  Thus, when you hear someone talking about Alzheimer’s, remember that they might mean “Alzheimer’s disease” or they might mean “dementia”.

Definitions

Aphasia Aphasia is an impairment of language ability.  It can affect language comprehension, spoken language, or ability to read or write.  A common, early sign, of aphasia in people with dementia is difficulty naming objects or difficulty getting a desired word to come out.

Apraxia Apraxia is the inability to perform already learned, coordinated tasks despite being physically capable of the action.  For example, loss of the ability to use a knife and a fork is a utensils apraxia.

Agnosia Agnosia is the inability to recognize familiar things.  Patients with dementia may lose the ability to recognize and name familiar objects.  They may lose recognition of family members or their home.  And they may not recognize that something is wrong with them.

Executive functioning The executive functions are the command-and-control functions of the brain.  The executive functions are critical for goal-oriented behavior.  These functions include initiation, planning, sequencing, monitoring, inhibition, and judgment.

REFERENCE

Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition, Text Revision.  American Psychiatric Association, Washington, D.C., 2000.

Moak Center for Healthy Aging ©
Updated December 2008