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Tuesday, January 29, 2013

Quantitative MRIs evade multiple sclerosis clinicoradiologic paradox

January 28, 2013

By Peter Sergo, medwireNews Reporter

Quantitative magnetic resonance imaging (MRI) can detect microstructural changes in the spinal cords of patients with multiple sclerosis (MS) that correlate with observed differences in clinical disability, according to a cross-sectional study in Neurology.

The identification of clinically relevant differences surpassed those that conventional MRI was able to detect, which were unable to explain the disconnect between spinal cord lesions and corresponding physical disability often observed in MS: the clinicoradiologic paradox.

"These findings support the concept that microstructural changes… contribute substantially to clinical disability in MS, and suggest that quantitative MRI measures have the ability to provide clinically relevant information beyond that which may be gleaned from measures of MRI lesion load alone," authors Jiwon Oh (Johns Hopkins University, Baltimore, Maryland, USA) and colleagues write.

A total of 124 patients underwent 3-T cervical spinal cord MRI and were grouped based on having two or fewer spinal lesions ("low-lesion" group) or three or more spinal lesions ("high lesions" group). The two groups were subsequently classified further based on a "low" versus "high" disability level.

The four subgroups underwent various, complementary quantitative MRI sequences that focused between the C3 and C4 vertebra of the spinal cord (axial cross-section) and provided numerous indices: fractional anisotropy, mean diffusivity, perpendicular diffusivity, parallel diffusivity, and magnetization transfer ratio (MTR).

With the exception of parallel diffusivity and MTR, the high-disability subgroups in both the low and high lesion count groups generally had a higher degree of abnormality in their MRI measures than the low-disability subgroups, enabling discrimination even after age and gender were controlled for.

The low lesion group showed a significant difference in MTR between the disability subgroups, which was not observed in the high lesion group. The authors explain that this measurement of myelin content may be less relevant to clinical disability in patients who have more spinal cord lesions due to axonal degeneration taking a larger toll or, alternatively, demyelination being too extensive.

The authors also suggest that the disability observed in patients with a high lesion load is related to the structural integrity of the tissue that remains rather than the magnitude of tissue loss, which underscores the importance of quantitative MRI indices.

"If confirmed prospectively, these techniques have the clinical utility in a variety of realms, including monitoring therapeutic efficacy, predicting disability progression, and as a surrogate outcome measure in clinical trials," Oh et al observe. "The need for predictive measures of disease progression is apparent as clinical practice of MS continues to evolve."



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