What is the role of MRI in the workup of Alzheimer disease (AD) in Down syndrome (DS)?

Updated: Nov 13, 2019
  • Author: Norberto Alvarez, MD; Chief Editor: Jasvinder Chawla, MD, MBA  more...
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Answer

Answer

Magnetic resonance imaging (MRI) studies have documented several developmental findings in persons with Down syndrome (DS), including the following:

  • Reduction in the whole brain volume (including cerebellum) and in the gray and white matter of the brain

  • Reduction in the volume of the hippocampus,

  • Focal reductions in the volume of the frontal and occipital lobes

  • Relative preservation of the temporal lobe with decreased volume of the planumtemporale and the superior temporal gyrus

MRI studies might show a decrease in the volume structures of the temporal lobe (eg, the hippocampus and the adjacent medial temporal lobe) in patients with DS who do not have dementia. Significant atrophy of the corpus callosum, an indication of neocortical atrophy (more obvious in the splenium), has also been demonstrated in persons with DS before the development of Alzheimer disease (AD).

MRI findings in symptomatic individuals are similar to those of computed tomography (CT) and reveal progressive atrophy of the brain with enlargement of the ventricular system.

MRI volumetric analysis of selective areas of the brain involving 19 adults with DS and AD and 39 adults with DS without AD found smaller volumes bilaterally in the hippocampus and caudate, right amygdala, and putamen and a larger volume of left peripheral CSF in individuals with DS and AD. This study suggests that significant reduction in medial temporal and striated volume reductions may be a reliable marker of AD in persons with DS. [85] However, age-related reduced volume in frontal, temporal, and parietal lobes, as well as an increased volume of peripheral CSF, have also been described in individuals with DS without clinical indications of dementia. [86]

These observations are in agreement with prior studies reporting cerebral atrophy and ventricular enlargement, suggesting brain atrophy, in individuals with DS when cognitive deficiencies were present, [84] or when regional differences with more involvement of the temporal horns were reported. [87]

Diffusion tensor imaging (DTI) is a noninvasive in vivo method that evaluates the microstructural properties of white matter (WM) by measuring the rate and direction of diffusion of water molecules in the neural tissue. DTI has been used extensively to study both brain aging and disease states such as AD.

Fractional anisotropy (FA) measures white matter changes and is expressed as 0, representing poor white matter integrity, or 1, representing good white matter integrity. A study involving 25 individuals with DS, 10 of whom had AD, showed lower FA values, mostly in circuits involving the frontal lobe, in adults with DS compared with controls. In these individuals, the abnormalities in the white matter were also associated with decreased performance in frontal executive functions but not with cognitive decline. [88] These findings may help us understand why frontal-dependent behavioral and executive function changes are among the earliest signs of AD. 

The summary of these observations is that CT/MRI studies in individuals with AD and DS consistently demonstrate abnormalities, even in the early stages of the disease; however, this might not be enough to establish the diagnosis of dementia, and clinical correlation is always needed. Serial CTs and or MRIs might be needed to differentiate older persons with DS who have dementia from those who do not.

In addition, CT/MRI is very useful to rule out other causes of neurological deterioration.


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