Jon stones use of CBT in MS to justify it is silly, they have different response to activity and exertion, the MS society Facebook is full of threads on the benefits of exercise. And often when CBT is used for fatigue in other illness it is unfortunately based on the bps model and being used because the fatigue is still medically unexplained. So they might not be suggesting pediatric MS, cancers or kidney disease are psychological but they do assert psychological behavioural factors sometimes causing the fatigue to a degree and being modifiable.