Ito_article_EU Neurology 10/03/2010 09:58 Page 108
Imaging
Progressive Supranuclear Palsy and Diffusion Tensor Imaging
Shoichi Ito
Associate Professor, The Office of Medical Education, Graduate School of Medicine, Chiba University, and Department of Neurology, Chiba University Hospital
Abstract
Progressive supranuclear palsy (PSP) is a neurodegenerative disease affecting multiple neural systems, particularly the extrapyramidal system.
Early differentiation of PSP from other diseases mainly featuring parkinsonism, such as Parkinson’s disease and multiple system atrophy, is
necessary because the therapeutic strategy and outcome are substantially different. Diffusion tensor imaging is a recently developed magnetic
resonance imaging (MRI) sequence that is able to non-invasively evaluate neural tracts. Two approaches may be used to measure diffusion
properties. One approach is to measure diffusion properties by setting the regions of interest on circular/square regions or along the tractography.
The other approach is to perform voxel-by-voxel analysis of the diffusion properties. There are several reports evaluating diffusion tensor
abnormalities in PSP, and regions with diffusion tensor abnormlities are distributed through frontal projection fibres, the anterior part of the corpus
callosum, superior longitudinal fasciculus, arcuate fasciculus, posterior thalamic radiations, internal capsule and superior cerebellar peduncles.
Here, diffusion tensor studies in PSP are reviewed and clinical applications, limitations and future perspectives of diffusion tensor analysis in PSP
are discussed.
Keywords
Progressive supranuclear palsy, diffusion-weighted imaging, diffusion tensor imaging, tractography, statistical parametric mapping, apparent
diffusion coefficient, fractional anisotropy, corpus callosum, superior longitudinal fasciculus, arcuate fasciculus, internal capsule, superior
cerebellar peduncles
Disclosure: The author has no conflicts of interest to declare.
Received: 9 March 2009 Accepted: 21 July 2009
Correspondence: Shoichi Ito, 1-8-1 Inohana, Chuo-ku, Chiba, 260-8670, Japan. E: sito@faculty.chiba-u.jp
Clinical Features of Progressive investigation of the pathophysiology of diseases. Recently, several new
Supranuclear Palsy MRI techniques have been developed, and one of the most important
Progressive supranuclear palsy (PSP) is a neurodegenerative disorder of these tools is diffusion-weighted imaging,
3
which can be used to
characterised by parkinsonism, supranuclear ophthalmoplegia, measure the diffusion of water molecules in the brain.
4
Brain diffusion
dysphagia and cognitive dysfunction. The National Institute of is influenced by tissue density, neuronal axon and vessel direction and
Neurological Disorders and Stroke (NINDS) PSP criteria are widely used capillary flow. The apparent diffusion coefficient (ADC) or mean
for clinical diagnosis.
1
However, the clinical phenotypes of pathologically diffusivity (MD) is a parameter that represents diffusion intensity, and
confirmed PSP patients are heterogeneous. Recently, PSP has been high ADC or MD values indicate increased diffusion intensity (see
clinically classified into two phenotypes: Richardson’s syndrome and Figure 1). Diffusion intensities along three orthogonal directions are
PSP-parkinsonism.
2
Those patients who have Richardson’s syndrome represented as λ1, λ2 and λ3, and MD values are calculated as [λ1, λ2,
are neurologically characterised by the classic features, including the and λ3]/3. Axial diffusivity (λ1) and radial diffusivity ([λ2 + λ3]/2) are
early onset of postural instability and falls, supranuclear vertical gaze occasionally used as additional measures to identify whether
palsy and cognitive dysfunction. PSP-parkinsonism is frequently differences in anisotropy may be caused by diffusion parallel or
misdiagnosed as Parkinson’s disease in its early clinical stage and is perpendicular to the white-matter fibres, respectively. Cytotoxic
characterised by asymmetrical onset, tremor and moderate initial oedema is a typical pathological condition in which decreased ADC
therapeutic response to levodopa. Differentiating between Richardson’s values are indicative of cerebral infarction
5,6
or other conditions. ADC
syndrome and Parkinson’s disease is not difficult, but differentiating values are increased by vasogenic oedema
7
or demyelination.
8
In
between PSP-parkinsonism and Parkinson’s disease is occasionally neurodegenerative diseases, ADC values are increased in affected
challenging. Early differentiation of these diseases is necessary because areas because of disruption of neuronal axons.
9,10
the therapeutic strategy and outcome are substantially different (e.g.
PSP patients have much worse prognosis). Diffusion Tensor Imaging
Diffusion tensor imaging was introduced as a new imaging modality in
Diffusion-weighted Imaging 1994.
11
Molecules inside neuronal axons have a low probability of
Magnetic resonance imaging (MRI) is a promising non-invasive tool crossing the myelin membrane, and thus brain diffusion in this
that supports or complements clinical diagnosis. It is also useful for the modality is usually anisotropic. Fractional anisotropy (FA) provides an
108 © TOUCH BRIEFINGS 2009
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