To investigate the pathophysiology of fatigue in MS, we assessed cerebral glucose metabolism (CMR-Glu) in 47 MS patients using PET and 18F-fluorodeoxyglucose. Applying the Fatigue Severity Scale (FSS), we first compared MS patients with severe fatigue (MS-FAT, n = 19, FSS > 4.9) and MS patients without fatigue (MS-NOF, n = 16, FSS < 3.7) on a pixel-by-pixel basis using Statistical Parametric Mapping (SPM95). Second, we compared FSS values of all 47 patients covering the whole range of this scale with CMRGlu using an analysis of covariance (SPM95). In addition, we determined global CMRGlu by region-of-interest analysis. Sixteen healthy subjects served as control subjects (CON). Global CMRGlu was significantly lower in both MS groups compared with CON (CON 43.3 +/- 6.9 mumol/100 mL/min, MS-FAT 34.7 +/- 4.4, MS-NOF 35.4 +/- 4.5) but was not related to fatigue severity. Comparing the two MS groups, SPM95 analysis revealed predominant CMRGlu reductions bilaterally in a prefrontal area involving the lateral and medial prefrontal cortex and adjacent white matter, in the premotor cortex, putamen, and in the right supplementary motor area of MS-FAT. In addition, there were CMRGlu reductions in the white matter extending from the rostral putamen toward the lateral head of the caudate nucleus. FSS values were inversely related to CMRGlu in the right prefrontal cortex. CMRGlu in the cerebellar vermis and anterior cingulate was relatively higher in MS-FAT than in MS-NOF patients. CMRGlu of both regions showed positive correlations with FSS values. Our data suggest that fatigue in MS is associated with frontal cortex and basal ganglia dysfunction that could result from demyelination of the frontal white matter.

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More than 50 % of patients with multiple sclerosis (MS) suffer from cognitive deficits. Attention is one of the most frequently affected cognitive functions. It has been shown that MS patients suffer from a specific but not necessarily from a generalized decrease in performance and that different severity grades of impaired attentional processing can be distinguished. Little is known about patterns of brain activation in MS patients with different grades of attentional deficits. The objective was to examine if different severity grades in attentional impairment are reflected by altered patterns of brain activation in specific attention tasks. In the present study cerebral activation induced by three attention tasks of different complexity was assessed in 14 MS patients and seven healthy controls by functional MRI (fMRI). Based on their performance on the tests recorded off-line with a computerized test battery and during the fMRI investigation, patients were classified as mildly and severely impaired. MS patients with mild impairment showed increased and additional activation of brain areas which were in part not activated in normal subjects. Those were located mainly in the frontal cortex and posterior parietal cortex. This effect decreased with increasing task complexity and was strongest for the alertness task. In MS patients with severe impairment no additional activation was found in prefrontal structures and activation in the premotor cortex was not significantly different from controls. These findings suggest that compensation in MS patients is in part achieved by functional integration of frontal and parietal association areas. The extent of compensation seems to depend on the brain's capacity to access additional brain structures. Exhaustion of this capacity may finally lead to severe cognitive impairment.

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This is the first long-term follow-up of patients who discontinued natalizumab. We did not observe a clinical, radiographic, or immunologic rebound phenomenon after discontinuation of natalizumab therapy.