Alzheimer’s disease and Other Cognitive Disorders
Reversible and Irreversible Cognitive Disorders
Carrie Steckl, Ph.D., edited by Natalie Staats Reiss, Ph.D.

Introduction

Often, mental health professionals classify cognitive disorders into two broad categories: those that are irreversible (i.e., not curable) and those that are reversible (i.e., curable). Dementias are irreversible, progressive, degenerative disorders that gradually reduce a person's ability to function in everyday life. A person with dementia cannot regain his or her previous level of functioning, even though some symptoms may be managed through treatment. Examples of irreversible dementias include Alzheimer's Disease, and Lewy Body Dementia,

On the other hand, the progression of reversible cognitive disorders can be halted by identifying the cause of the symptoms and properly treating the underlying disorder. With appropriate treatment, a person's previous level of functioning can be restored. Examples of reversible cognitive disorders are pseudodementia and delirium, which will be described later.
Reversible & Irreversible

The types of reversible and irreversible disorders that we discuss is this topic center are classified as "Delirium, Dementia, and Amnestic and Other Cognitive Disorders" in the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSM-IV; the "gold standard" manual used by mental health professionals to diagnose disorders). However, as dementia is the most common cognitive disorder, we will start with a discussion of this condition. Regardless of the diagnosis, the common denominator among all of the conditions discussed here is a significant problem with memory and/or other areas of cognitive functioning that represents an obvious change from the person's previous level of functioning.
Dementia
Many people mistakenly use dementia as a synonym for Alzheimer's disease. This use of the word is inaccurate; "dementia" is an umbrella-like term that refers to any brain syndrome that causes multiple cognitive deficits. In other words, saying someone has "dementia" is similar to saying that someone has a fever; you are not specifying the exact cause of the symptoms.
A person with dementia can experience all sorts of problems, including:
• Impaired Memory (especially the ability to remember recent events and newly learned facts)
• Impaired Language Skills (decreased ability to communicate to others and understand what is being communicated)
• Impaired Orientation (not knowing who one is, where one is, and/or what time it is)
• Impaired Judgment (impaired ability to make decisions regarding personal, interpersonal, financial, and/or medical affairs)
• Impaired Executive Functioning (impaired ability to plan and carry out daily tasks and make decisions).
Dementia can be caused by one medical condition or by multiple medical problems. Most dementias are caused by one of the following:
• Alzheimer's Disease, which accounts for 50-70% of all dementia cases
• Vascular Disease, which accounts for 15-20% of all dementia cases and includes strokes (disruptions in the blood supply to the brain) and transient ischemic attacks (TIAs, or mini strokes)
• Lewy Body Disease, which accounts for up to 20% of all dementia cases
We will concentrate most of our discussion on dementia due to Alzheimer's disease, Vascular Disease, and Lewy Body Disease because these conditions are most common. However, there are other medical conditions worth mentioning that can also cause dementia (at a much lower rate). They include HIV/AIDS, head trauma, Parkinson's disease, Huntington's disease, Pick's Disease, Creutzfeldt-Jakob Disease, normal pressure hydrocephalus, and Wernicke-Korsakoff Syndrome.
Mixed Dementia
Dementia caused by multiple medical conditions is called Mixed Dementia or - in the DSM-IV - dementia due to "multiple etiologies." The most common form of Mixed Dementia is dementia due to both Alzheimer's and Vascular Disease, both of which we describe below.
In cases where a clear reason for the dementia cannot be determined, the dementia is referred to as Dementia NOS (not otherwise specified). There are a couple of reasons a diagnosis of Dementia NOS might be given. For example, a person may clearly show signs of dementia, but the clinician does not have enough information to make an accurate diagnosis. In this case, the NOS is a temporary diagnosis that will be changed once the clinician has gathered more information. In rare cases, every known cause of dementia is ruled out (e.g., found not to be a cause), so a diagnosis of Dementia NOS is given because the reason for the person's symptoms is truly unknown.