Absence of MRI exams in epidemiological studies can leads to clinical overdiagnosis of Alzheimer's disease and underdiagnosis of vascular dementia

CORRESPONDENCE

Absence of MRI exams in epidemiological studies can leads to clinical overdiagnosis of Alzheimer's disease and underdiagnosis of vascular dementia

TO THE EDITOR

We would like to comment some methodological issues that arised from the interesting paper of Tascone et al.¹ and that did not were cleared in the discussion. Until and unless we have neuropathological confirmation of diagnostic accuracy, our conclusions must be seriously questioned since we all know that the definitive diagnoses of Alzheimer's disease (AD), vascular dementia (VaD), and other dementias are based on neuropathological criteria. Obviously, this limitation should not hinder epidemiological studies like the excellent work of Tascone et al. However, caution should be taken related to the prevalence rates of each dementia form, since some of them are almost exclusively diagnosed with expensive neuroimaging methods as is the case of MRI for the correct diagnosis of an important and frequent form of dementia: Binswanger disease or subcortical vascular dementia.² As the authors did not mentioned if they used CT or MRI scans in their patients and because MRI is an expensive method, we assume that most of their patients probably was examined with CT scans.

The predominance of AD diagnosis found by the authors is remarkable (62.8%), but is in consonance with international literature. These findings, however, may reflect an overdiagnosis of Alzheimer's disease to the detriment of vascular dementia, since individuals with silent cerebrovascular disease or even subcortical cerebrovascular disease may not be detected without using MRI scans. In fact, in their study the diagnosis of "other dementias" which comprises patients with vascular dementia (VaD) and other forms of dementia is surprisingly low (14.2%), contradicting vascular dementia rates in other studies.³ Adding contribution to this debate, we should mention that one of the most important authorities in the field postulated that the two main causes of VaD - stroke and ischemic heart disease (IHD) - may be responsible for the majority of cases of dementia in the elderly. This author remembered that cerebrovascular disease (CVD) is the second leading cause of death worldwide. About 1/3 of stroke survivors [range: 25-41%] 65 years old and above develop VaD within 3 months following the ictus. In the USA alone, 125,000 new cases/year of VaD occur after ischemic stroke (about 1/3 of the 360,000 incident cases of AD). Therefore, more than 1 million elderly people are currently affected by poststroke VaD in the USA. Besides that, IHD leading to congestive heart failure (CHF) will become the leading cause of disability worldwide. Vascular cognitive impairment occurs in 26% of patients discharged from hospitals after treatment for CHF. Cognitive dysfunction correlates with left ventricular dysfunction and systolic blood pressure below 130 mm Hg. CHF is a leading cause of hospital admissions in Western nations (4.5 million cases in the USA alone) and is a growing problem in developing countries. Furthermore, over 800,000 patients/year undergo coronary artery bypass graft (CABG) surgery worldwide, including 300,000 patients in the USA. Measurable cognitive dysfunction occurs post-CABG in 80-90% of patients at hospital discharge. Long-term (5 years) incidence of cognitive defects is 42% 4,5.

Other factor that may have contributed to the low incidence of VaD in this study should be the psychiatric orientation of their service. VaD patients, mainly those resulted from multi-infarct brain lesions, tend to seek for attention in neurological services.

Leonardo Caixeta

Vânia Lúcia Soares

Cândida Dias Soares

Cognitive and Behavioral Neurology Unit

Hospital das Clínicas/Federal University of Goiás

• 1. Tascone LS, Marques RCG, Pereira EC, Bottino C. Characteristics of patients assisted at an ambulatory of dementia from a university hospital. Arq Neuropsiquiatr 2008; 66: 631-635.
• 2. Korczyn AD. The underdiagnosis of the vascular contribution to dementia. J Neurol Sci 2005; 15:229-230: 3-6.
• 3. Korczyn AD. Mixed dementia-the most common cause of dementia. Ann N Y Acad Sci 2002;977:129-34.
• 4. Román GC. Vascular dementia may be the most common form of dementia in the elderly. J Neurol Sci 2002; 15:7-10.
• 5. de la Torre JC. Alzheimer's disease prevalence can be lowered with non-invasive testing. J Alzheimers Dis 2008; 14:353-359.

Publication Dates

• Publication in this collection
  05 June 2009
• Date of issue
  June 2009