Dementia: Update for the Practitioner

Recognition of Vascular Dementia, Dementia with Lewy Bodies, and Frontotemporal Dementia
Lawrence S. Honig, M.D., Ph.D.

Prevalence of Non-Alzheimer's Dementias

Considerations of dementia prevalence are complicated by the fact that different disorders may occur in overlapping fashion. For example, Lewy-body dementia clearly overlaps with Alzheimer's disease. Dementia with Lewy bodies is present in about 15 and 30 percent of cases diagnosed by the pathologist as also having Alzheimer's disease. Conversely, of cases showing Lewy-body dementia, 60 to 90 percent also have Alzheimer's pathology. Thus, to a degree, the pathological hallmarks of Alzheimer's disease—plaques, tangles, and the associated synaptic and neuronal loss—are features in the large majority, but definitely not all, of Lewy-body dementia cases. Different series will then show Lewy-body dementia, Alzheimer's disease, or combination diagnosis, depending on the exact pathological criteria espoused for Alzheimer's disease—how frequent plaques, how extensive tangles, and in what locations do these findings prompt diagnosis of Alzheimer's disease?

Furthermore, the newest staining techniques and greater sensitivity of these neuropathological tests show that Lewy bodies may be present in up to 60 to 65 percent of Alzheimer's brains. Thus, if the criterion for Lewy-body dementia is that there is at least one Lewy body, then 60 percent of dementias will be termed Lewy-body disease.

In most series, frontotemporal dementia (FTD) represents 5 to 10 percent of cases. This number may again relate in part to underrepresentation of Alzheimer's and overrepresentation of the atypical dementias in autopsy series at university medical centers. Nonetheless, FTD does occur in a significant number of people with dementia, often in those with earlier onset, in their 40s or 50s. Frontotemporal dementia may be more troubling to affected individuals and their families because patients may still be employed while suffering early symptoms.

Vascular dementia, like Lewy-body dementia overlaps with Alzheimer's disease. Strokes are extremely common in the elderly. Depending on the radiologist reading the CT or MRI, the majority of elderly people may have a lesion that would qualify as a stroke, stroke-like micro-vascular disease, or cerebrovascular disease. Diagnosis of vascular dementia is dependent on the criteria used. If the criteria are a stroke and dementia, then depending on the radiologist, a very large fraction of elderly patients could be diagnosed with vascular dementia.

In pathological series, infarcts are seen in about 35 percent of cases. Neuropathological infarcts are seen less often than the radiologist sees them, but more often than clinically denoted. Clinical strokes occur in about 10 percent of people over the age of 65 or 75, pathological strokes are described by the neuropathologist in about 35 percent of cases, and radiological signs may be present in over 70 percent of cases.

Depending on the series and the criteria, vascular dementia represents somewhere between 5 and 20 percent of cases. A large number of cases have mixed Alzheimer's pathology and vascular pathology.

Doing a history and examination allows us to detect some of the features of these atypical dementias. In many cases, neuroimaging can be helpful, and in a few cases other laboratory tests can be useful in differentiating between these atypical disorders and Alzheimer's disease. This is the rationale for performing certain laboratory testing, including thyroid functions, tests of B12, and infection status, and other tests like spinal-fluid analysis, EEG, SPECT, and PET.


	Symptoms Generally Inconsistent with Alzheimer's Disease Sudden onset Presenting focal neurologic findings -e.g., hemiparesis, hemianesthesia, hemianopia Seizures early in the course of the illness Presenting Sx of abnormal gait/coordination Preservation of memory function

	Certain signs and symptoms are generally inconsistent with diagnosis of Alzheimer's disease. Courtesy of Dr. Lawrence Honig


	Signs Atypical for Alzheimer's Disease Dominant non-memory Sx -e.g., language, praxis, visuospatial dysfunction Prominent behavioral, personality, psychotic Sx Early parkinsonism -e.g., resting tremor, bradykinesia, cogwheeling Early prominence of bulbar/brainstem signs Unexplained motor or reflex asymmetries Unexplained (early) UMN signs (e.g., Babinski) Unexplained LMN signs (e.g., fasciculations)

	Certain signs and symptoms are atypical for Alzheimer's disease and thus more suggestive of an atypical dementia. Courtesy of Dr. Lawrence Honig


	Atypical Dementias Chronic dementias of the elderly atypical for Alzheimer's disease Parkinsonian syndromes - PD and Lewy-body dementias, PSP, CBGD, etc. Focal cortical syndromes - Frontotemporal Dementias, PSP, CBGD Vascular syndromes Rare genetic, metabolic, toxic, structural disorders

	There are a number of chronic dementias of the elderly that are atypical for Alzheimer's disease. Courtesy of Dr. Lawrence Honig


	Symptoms and Signs of Atypical Dementia

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