MS is another of the mysterious fatiguing disorders - so its worthwhile to pay attention to it The take home thing here is that while they did find anxiety and depression those factors were only weakly correlated with fatigue. Like CFS sleep has a complex but intimate association with Fatigue - the sleep factor is there but its hard to figure out. They actually have a neurological Fatigue index - they are ahead of us there. I would really like to get that. Its intriguing because its a documented neurological illness that produces fatigue where its not so prominent in other neurological illnesses.....By definition it cannot be 'psychological'. Instead MS must affect some part of the brain that effects fatigue.