Phenomenological Psychology

Phenomenological Psychology header image

What Are the Principal Neurodegenerative Diseases?

June 15th, 2009 by David Kronemyer · No Comments

DSM-IV defines the principal neurodegenerative diseases as delirium, dementia, amnestic disorders and cognitive disorder NOS. It classifies them as “cognitive disorders,” which is somewhat of a misnomer as many other DSM pathologies also involve cognitive dysfunction. They previously were classified as “organic mental disorders,” which also was unsatisfactory as many other DSM pathologies also have a biological etiology. A possible (albeit unsatisfactory) resolution of this nomenclature issue is that cognitive dysfunction is a necessary symptom for the “cognitive” disorders whereas it is a possible (or even probable) symptom for other disorders, though not necessary.(1) While they include a cognitive component DSM-IV excludes normal cognitive deterioration resulting from aging (“age-associated memory impairment”) and cognitive disruption caused by other psychiatric outcomes such as major depression.

The cognitive presentations they share are as follows. All involve: (1) a “cognitive” component such as amnesia, aphasia, loss of capacity to construct visuospatial relationships and disruption of executive functions. Patients may be inattentive or easily distractible and have disorganized thinking or an altered level of consciousness. They may be emotionally labile. See further descriptions infra. (2) Reduction of fine motor skills characteristic of apraxia and the ability to anticipate and coordinate future bodily movements. (3) Neurobehavioral characteristics similar to those found with major depression, including apathy and irritability. (4) Subjective mental distress and loss of ability to function in social contexts.

The cognitive and other features that make each of them distinct diagnostic entities are as follows:

Delirium. DSM-IV 293 defines delirium as a sudden change in mental functioning occurring over a short period of time. Diagnostic criteria are a disturbance of consciousness (reduced clarity of awareness of the environment) with reduced ability to focus, sustain or shift attention; accompanied by change in cognition (such as memory deficit, disorientation, language disturbance) or the development of a perceptual disturbance.

From a differential diagnosis standpoint the most significant factor is that delirium has acute onset. Its course is characterized by a sudden drop-off from baseline followed by a return to baseline once treated. Because of its quick and unexpected onset immediate medical evaluation and treatment is necessary.

It is caused by (a) a general medical condition such as shock, low blood pressure, dehydration or infection; or (b) drug reaction, sensory deprivation or substance abuse or withdrawal. Risk factors include injury, pain or stress; substance abuse; physical disease such as lung, liver, heart, kidney or brain disease; temporary physiological disruptions such as metabolic or electrolyte disorders; and even temporary psychological disruptions such as becoming disoriented or being in an unfamiliar environment.

Dementia. Dementia is a progressive loss of intellectual functioning occurring over an extended time period. The primary symptoms set forth at DSM-IV 294 are the development of multiple cognitive deficits manifested by both memory impairment and at least one or more other cognitive disturbance such as aphasia, apraxia, agnosia or other perturbation in executive ability. These cognitive deficits must cause significant impairment in social or occupational functioning and represent a significant decline from a previous level of functioning.

From a differential diagnosis standpoint dementia’s distinguishing feature is gradual onset and continuing cognitive decline. Its course is lengthy and may last from months to years during which the patient will experience a gradual decline in cognitive ability, motor skills, impulse control and emotional affect.

Dementia can be caused by thyroid disease, depression, Vitamin B12 deficiency, reaction to medication, long-term alcohol abuse or stroke. Other possible causes are Alzheimer’s disease, Pick’s disease, Huntington’s, Downs Syndrome, Creutzfeldt-Jacob, AIDS or Parkinson’s disease. The primary risk factor is age. Dementia is rare for persons under 50 years old. Other risk factors include head injury and family genetics (early onset of mutations in certain chromosomes and late onset of mutations in others).

Amnestic disorders. Amnestic disorders involve deficiencies in (a) encoding and retrieving memory; and (b) retrograde and anterograde amnesia.

(a)  Encoding and retrieving memory. Patients are disoriented in space and time. They may not know who they are or simple facts such as the day of the week or the identity of the president. To be diagnosable under DSM-IV 294.0 the patient must be (a) impaired in her/his ability to learn new information or unable to recall previously learned information; the memory disturbance must be sufficiently severe to cause marked impairment in social or occupational functioning and must represent a significant decline from a previous level of functioning; it must not occur exclusively during the course of delirium or dementia; and it must be the direct physiological consequence of a general medical condition (including physical trauma).

“Memory” typically is divided into short-term memory (retaining information for a minute or less) and long-term memory (holding it for a longer period of time). Long-term memory further subdivides into recent memory (new learning) and remote memory (old information). In order to convert new information into long-term memory one must pay attention to it (registration); then store it (encoding); then retain it (consolidation). To recall it one must be able to retrieve it. While amnestic disorders may affect any of these steps, most frequently they involve deficits in short-term memory and recent memory.

(b)  Amnesia. Retrograde amnesia is loss of information learned prior to the event; anterograde amnesia is inability to establish memory thereafter. Amnestic disorders most frequently involve anterograde amnesia. This makes sense because of the patient’s inability to encode and retrieve short-term and recent memory.

Amnestic disorders result from exposure to a substance such as an environmental toxin, medication or drug of abuse; traumatic brain injury (stroke, concussion, accidents involving oxygen deprivation to the brain); tumors; encephalitis; epilepsy; and other general medical conditions that produce a memory disturbance. A variety of psychological-type memory tests are available as diagnostic tools. In severe cases brain anatomy tests may include CT, MRI or PET scans.

Amnestic disorders are treatable and will abate (or the period of amnesia eventually shorten) with physical recovery from the underlying disorder. Memory can be rehabilitated using association techniques and memory exercises. The symptoms of memory loss also may be alleviated by primes such as lists, notes, calendars and timers.

Cognitive disorder NOS. As is typical DSM-IV at 294.9 includes a final “catch-all” category of cognitive disorder NOS, which is for presentations that are characterized by cognitive dysfunction presumed to be due either to a general medical condition or substance use that do not meet criteria for any of the other cognitive disorders. Examples include mild neurocognitive disorder and postconcussional disorder. A variety of different factors go into the diagnosis of any cognitive disorder, which this category is designed to encompass. Treatment should be the same as that for the underlying pathology possibly accompanied by memory-enhancing therapy similar to that for the amnestic disorders.


(1) If they still were called “organic mental disorder” then this would entail that organic dysfunction was a necessary component of a diagnosis whereas it would not be necessary for other DSM pathologies. This seems unlikely though particularly in the case of psychotic disorders which involve delusions or hallucinations. While the applicable DSM-IV categories do not specifically require for them to have an organic cause one heavily is implied by the text, which dwells on “associated laboratory findings” in a way unlike that for any other DSM-IV disorder. The main reason why this is interesting is because it implicates historical theory of mind problems such as the distinction between “mind” and “body.”