Detecting cognitive fatigue in multiple sclerosis: method matters.

BACKGROUND: Fatigue is a frequently reported and debilitating symptom in multiple sclerosis (MS). Cognitive fatigue (CF) can be defined as decreased performance with sustained cognitive effort. The effectiveness of the Paced Auditory Serial Addition Task (PASAT) and the Computerized Test of Information Processing (CTIP) at detecting CF was examined, as was the impact of methodology. Subjective fatigue was measured using the Fatigue Impact Scale (FIS). The relationship between objective and subjective fatigue was examined. METHODS: 70 MS and 72 healthy controls (HC) completed the PASAT (3″ and 2″), CTIP, and FIS as part of a larger battery. RESULTS: The MS and HCs performed worse on cognitively demanding tasks. Depending on methodology, PASAT performance varied between groups at the 3″ inter-stimulus interval (ISI) and the MS group showed greater susceptibility to CF as their ability to meet task demands declined as the task progressed. CTIP performance for both groups varied differently over time depending on task. The relationship between subjective and objective measures of fatigue varied depending on methodology, with PASAT generally correlating well with the Cognitive Dimension of the FIS. CONCLUSIONS: The PASAT is a sensitive measure of CF in MS. Additional information is obtained with different scoring methods, with percent dyad scoring method being most sensitive to CF. The ability to detect a relationship between objective and subjective measures varied with methodology.

Activation patterns in multiple sclerosis on the Computerized Tests of Information Processing.

RATIONALE: Multiple sclerosis (MS) patients exhibit cognitive deficits that negatively impact quality of life. The Relative Consequence Model suggests that problems with information processing speed (IPS) may be the basis for many of these cognitive difficulties. OBJECTIVE: To investigate, with functional magnetic resonance imaging (fMRI), if an IPS task (the Computerized Test of Information Processing (CTIP)) would reveal neurophysiological differences between MS patients and matched controls. METHODS: Performance and neural activation were investigated in twelve cognitively impaired MS patients and 12 matched controls as each performed the CTIP. The CTIP measures reaction time (RT) and errors on three tasks (simple RT, choice RT and semantic search RT) with increasing cognitive demands. RESULTS: Participants demonstrated increased RT with increased task complexity. Patients showed longer RTs for the choice RT condition than controls but the pattern of performance across tasks did not vary between groups. Errors were not significantly different between groups. Imaging results for both the choice and the semantic search conditions revealed significant differences between groups involving a compensatory increase in activation in MS participants compared to controls in prefrontal cortex and right temporal gyri. However, there were also areas of decreased activity in MS participants when compared with controls in left temporal gyri. CONCLUSIONS: Significantly different neural activation patterns between MS patients and controls were associated with IPS, as measured by the CTIP.