Dementia in Alzheimer's Disease

• F00 Dementia In Alzheimer's Disease
• F00.0 Dementia In Alzheimer's Disease With Early Onset
• F00.1 Dementia In Alzheimer's Disease With Late Onset
• F00.2 Dementia In Alzheimer's Disease, Atypical Or Mixed Type

F00 Dementia In Alzheimer's Disease

Alzheimer's disease is a primary degenerative cerebral disease of unknown etiology, with characteristic neuropathological and neurochemical features. It is usually insidious in onset and develops slowly but steadily over a period of years. This period can be as short as 2 or 3 years, but can occasionally be considerably longer. The onset can be in middle adult life or even earlier (Alzheimer's disease of presenile onset), but the incidence is higher in later life (Alzheimer's disease of senile onset). In cases with onset before the age of 65-70, there is the likelihood of a family history of a similar dementia, a more rapid course, and prominence of features of temporal and parietal lobe damage, including dysphasia or dyspraxia. In cases with a later onset, the course tends to be slower and to be characterized by more general impairment of higher cortical functions. Patients with Down's syndrome are at high risk of developing Alzheimer's disease.

There are characteristic changes in the brain: a marked reduction in the population of neurons, particularly in the hippocampus, substantia innominata, locus ceruleus, and temporoparietal and frontal cortex; appearance of neurofibrillary tangles made of paired helical filaments; neuritic (argentophil) plaques, which consist largely of amyloid and show a definite progression in their development (although plaques without amyloid are also known to exist); and granulovacuolar bodies. Neurochemical changes have also been found, including a marked reduction in the enzyme choline acetyltransferase, in acetylcholine itself, and in other neurotransmitters and neuromodulators.

As originally described, the clinical features are accompanied by the above brain changes. However, it now appears that the two do not always progress in parallel: one may be indisputably present with only minimal evidence of the other. Nevertheless, the clinical features of Alzheimer's disease are such that it is often possible to make a presumptive diagnosis on clinical grounds alone.

Dementia in Alzheimer's disease is at present irreversible.

Diagnostic Guidelines

The following features are essential for a definite diagnosis:

(a) Presence of a dementia as described above.

(b) Insidious onset with slow deterioration. While the onset usually seems difficult to pinpoint in time, realization by others that the defects exist may come suddenly. An apparent plateau may occur in the progression.

(c) Absence of clinical evidence, or findings from special investigations, to suggest that the mental state may be due to other systemic or brain disease which can induce a dementia (e.g. hypothyroidism, hypercalcaemia, vitamin B12 deficiency, niacin deficiency, neurosyphilis, normal pressure hydrocephalus, or subdural haematoma).

(d) Absence of a sudden, apoplectic onset, or of neurological signs of focal damage such as hemiparesis, sensory loss, visual field defects, and incoordination occurring early in the illness (although these phenomena may be superimposed later).

In a certain proportion of cases, the features of Alzheimer's disease and vascular dementia may both be present. In such cases, double diagnosis (and coding) should be made. When the vascular dementia precedes the Alzheimer's disease, it may be impossible to diagnose the latter on clinical grounds.

Includes:
* primary degenerative dementia of the Alzheimer's type

Differential Diagnosis
Consider: a depressive disorder (F30-F39); delirium (F05); organic amnesic syndrome (F04); other primary dementias, such as in Pick's, Creuzfeldt-Jakob or Huntington's disease (F02.-); secondary dementias associated with a variety of physical diseases, toxic states, etc. (F02.8); mild, moderate or severe mental retardation (F70-F72).

Dementia in Alzheimer's disease may coexist with vascular dementia (to be coded F00.2), as when cerebrovascular episodes (multi-infarct phenomena) are superimposed on a clinical picture and history suggesting Alzheimer's disease. Such episodes may result in sudden exacerbations of the manifestations of dementia. According to postmortem findings, both types may coexist in as many as 10-15% of all dementia cases.

F00.0 Dementia In Alzheimer's Disease With Early Onset

Dementia in Alzheimer's disease beginning before the age of 65. There is relatively rapid deterioration, with marked multiple disorders of the higher cortical functions. Aphasia, agraphia, alexia, and apraxia occur relatively early in the course of the dementia in most cases.

Diagnostic Guidelines

As for dementia, described above, with onset before the age of 65 years, and usually with rapid progression of symptoms. Family history of Alzheimer's disease is a contributory but not necessary factor for the diagnosis, as is a family history of Down's syndrome or of Iymphoma.

Includes:
* Alzheimer's disease, type 2
* presenile dementia, Alzheimer's type

F00.1 Dementia In Alzheimer's Disease With Late Onset

Dementia in Alzheimer's disease where the clinically observable onset is after the age of 65 years and usually in the late 70s or thereafter, with a slow progression, and usually with memory impairment as the principal feature.

Diagnostic Guidelines

As for dementia, described above, with attention to the presence or absence of features differentiating the disorder from the early-onset subtype (F00.0).

Includes:
* Alzheimer's disease, type 1
* senile dementia, Alzheimer's type

F00.2 Dementia In Alzheimer's Disease, Atypical Or Mixed Type

Dementias that do not fit the descriptions and guidelines for either F00.0 or F00.1 should be classified here; mixed Alzheimer's and vascular dementias are also included here.