Lewy Body Dementia

As the population has aged over the past 20 years, recognition of dementia has improved. With increased recognition, it is clear that not all dementia is of the Alzheimer's type. The recently described Lewy body dementia, also known as dementia with Lewy bodies (DLB), is generally recognized as among the more common “new” dementias. The eponymous inclusion bodies were first reported in 1912, whereas case reports of this new type of dementia appeared during the 1980s.

Lewy bodies are spherical, eosinophilic, cytoplasmic inclusion bodies first described in subcortical nuclei in Parkinson's disease. Diffuse Lewy body disease was first described in 1984. Patients with diffuse (i.e., cortical as well as subcortical) Lewy bodies also often have plaques. The clinical history usually includes cognitive impairment, fluctuating severity, and parkinsonian movement disorder. Autopsy series find that 15% to 25% of all elderly demented patients have Lewy bodies, many with plaques, some with tangles, and many with evidence of ischemic damage as well. Lewy body disease may be the most common group of dementias after Alzheimer's-type dementia, although most cases of dementia seen clinically are mixed in symptomatology as well as pathology. Prevalence has been cited as up to 26.3% of all dementia and up to 5% of the general population, with incidence of 0.1% to 3.2% per year for all new dementia cases. Gender distribution is even, and age of onset is after 40 years but most commonly after 75 years. Survival is thought to be approximately 8 years, but more rapid (2 years) and much more indolent (20 years) courses have been described.

Consensus guidelines for clinical diagnosis of DLB were developed by Ian G. McKeith and colleagues in 1996. First, as common to dementias, there must be progressive cognitive decline that interferes with functioning. Memory impairment might not appear early but occurs during the disease course. Loss of attention, visuospatial skills, and frontal/ subcortical skills all may be evident. The clinical picture must include at least one of the following: fluctuating attention and cognition, well-formed visual hallucinations, and spontaneous parkinsonism. Two of these features make probable DLB; one feature makes a possible diagnosis. Supportive features include antipsychotic sensitivity, syncope and transient loss of consciousness, delusions and other hallucinations, and depression.

The diagnosis of DLB is made clinically; neither laboratory studies nor imaging are helpful. Although there is association with the APOE4 allele, knowledge of APOE status is not helpful in the diagnosis of an individual or helpful in counseling family members about risk of this dementia. Overall, DLB appears to be no more familial than Parkinson's disease.

The clinical diagnostic signs of Lewy body dementia are hallucinations, fluctuating attention and performance, and (often subtle) parkinsonism. Hallucinations are most often visual, vivid, and (often) not threatening. They are well-formed, three-dimensional images often of people or animals, and the patient may find them more puzzling than distressing. Persecutory delusions can occur as well and are threatening to the patient. Fluctuation is much more marked than is seen in other dementias; it may occur day to day or more quickly. It may resemble delirium. Compared with patients with Alzheimer's disease, patients with DLB are much more likely to (a) have daytime lethargy, (b) sleep more than 2 hours during the daytime, (c) stare into space at length, and [Page 323](d) have episodes of disorganized speech. Attempts have been made to find neuropsychological differences between DLB and Alzheimer's dementia, particularly tests that can be used bedside. Executive functioning is more likely impaired, and memory (as measured by the Folstein Mini-Mental State) is less impaired in DLB than in Alzheimer's disease. Patients with DLB are more likely to be distracted by irrelevant visual stimuli during interview or testing and have more difficulty in set shifting. They may, for instance, be more likely to bring in material from a previous question than to address the current question.

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