Defined as a clinical syndrome involving progressive deterioration in multiple areas of cognitive functioning, dementia is a major cause of disability, institutionalization, and increased mortality among the elderly.1 Although it can occur in younger persons too, dementia is typically associated with aging. It is often seen as a disease that cannot be prevented or cured. However, there is increasing evidence that some types of dementia can be successfully treated or even reversed.
In the case of the most common senile dementia, Alzheimer disease (AD), treatments are now available that can significantly slow the rate of cognitive decline. Other types of dementia, such as those resulting from vasculitis or other forms of inflammation, can be halted or reversed if they are properly diagnosed and treated in a timely manner.
EPIDEMIOLOGY
Currently, 24 million persons worldwide are thought to have some form of dementia. This number is likely to increase by 100% in the next 20 years as the number of persons older than 65 years doubles from about 500 million to almost 1 billion.1
AD is the most common dementing disorder, affecting approximately 4.5 million persons in the United States.2 Vascular dementia (VaD) is the second most prevalent dementia after AD in persons older than 65 years.1 However, the frequency distribution of dementia subtypes is somewhat different in younger persons.
A study of the relative frequency of various types of dementia among patients younger than 65 years who had been referred to a tertiary center in Athens, Greece, found that of a total of 107 patients with presenile dementia, 38 (35.5%) had AD, and 27 (25.2%) had frontotemporal dementia (FTD).3 Another 15 patients (13.9%) had dementia caused by metabolic deficits, such as folic acid(Drug information on folic acid) or vitamin B12 deficiency.
The researchers also reported that VaD and Lewy body dementia (LBD), both of which are common in elderly persons, were relatively rare in this patient population (7.4% and 2.8%, respectively). Dementia was secondary to other neurodegenerative diseases in 12 (11.2%) of the patients.
Although AD and FTD accounted for the majority (≈60%) of all cases of presenile dementia, dementia was due to potentially reversible causes in a significant proportion (13.9%) of patients.
DIFFERENTIAL DIAGNOSIS
Dementia may be reversible in a considerable number of patients, not only those under age 65 years.4,5 Therefore, it is extremely important to properly diagnose dementia in patients presenting with steadily deteriorating cognitive functioning.
Neuroimaging is a tool that is becoming increasingly important in the diagnosis and assessment of dementia, according to a recent article by Jennifer L. Whitwell, PhD, and Clifford R. Jack, MD, of the Department of Radiology, Mayo Clinic, Rochester, Minnesota.2 In their article, published in Neurologic Clinics, they describe different current neuroimaging modalities and discuss their advantages and disadvantages.
CT scans are relatively inexpensive, are widely available, and can often be helpful in determining the cause of rapid decline in cognitive function, the authors point out. They note, however, that MRI has a number of advantages over CT in the differential diagnosis of dementia. These include better tissue contrast and resolution as well as the ability to detect focal temporal lobe abnormalities.
Furthermore, MRI does not involve the use of ionizing radiation, which carries some risks, especially when serial studies involving repeated measures over time are required, Whitwell and Jack note. Moreover, because MRI is more sensitive to vascular changes (especially in subcortical regions) than CT, it is better able to identify the typical features of VaD, which include cortical infarctions, lacunar infarcts, and diffuse white matter hyperintensities, the authors contend.
In addition to structural and functional MRI, positron emission tomography and single-photon emission CT are also being used to aid in the differential diagnosis and early detection of dementia. These imaging techniques also can be used to track disease progression and to monitor the effects of various treatments.2
One of the most important developments in the field of neuroimaging in the past decade has been the ability to image amyloid in the brain.2 Amyloid plaques and neurofibrillary tangles are the hallmark pathological features of AD. The ability to identify plaques in living subjects has the potential to revolutionize diagnosis and management, the authors note.
Although in the past neuroimaging of dementia has focused on AD, research is increasingly being done with patients with non-AD dementias, such as FTD, VaD, and LBD. According to a review article by Paul M. Kemp, MD, and Clive Holmes, MD, of the Department of Nuclear Medicine, Southampton University Hospitals Trust, United Kingdom, it is very important to differentiate AD from LBD.6 LBD is the third most common type of dementia after AD and VaD. Differential diagnosis can be challenging because there is considerable overlap in the clinical presentations of AD and LBD, especially during the early stages, the authors note.
Most important, antipsychotics (neuroleptics) must be used with great caution in patients with cerebral Lewy bodies because antipsychotics can provoke a parkinsonian crisis in up to 80% of patients with LBD, which can be fatal in about 50%.6 The first-line treatment of psychotic symptoms in patients with LBD are acetylcholinesterase inhibitors. If antipsychotics are used as the second-line treatment, they should be introduced with extreme caution and at a low dosage.6
