These studies indicate that cortical lesions should be considered major contributors to disease burden in patients with MS, considering the substantial amount of neuronal pathology that occurs in cortical lesions. It is possible that ambulatory decline is modulated significantly by neuronal damage in motor and sensory cortex. Further, 40% to 70% of all individuals diagnosed with MS exhibit various aspects of cognitive deficits (Rao et al., 1991; Beatty et al., 1995). Functions most commonly affected involve learning, memory, and information processing (Rao et al., 1991). Correlation between decreased cerebral metabolism and increased MRI lesion load with cognitive dysfunction in MS was demonstrated by positron emission tomography studies (Blinkenberg et al., 2000). Although cognitive impairment in MS patients has been attributed to subcortical white matter lesions, reconciliation between the anatomical location of the subcortical lesions and the identified cognitive deficits is often problematic because they do not match. It is probable given the extent and nature of damage to cortical neurons in many MS brains, however, cortical lesions provide an additional biological substrate for functional impairment.
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