This might be what you are thinking of. Right Arcuate Fasciculus Abnormality in Chronic Fatigue Syndrome, 2014, Zeineh, Montoya et al This also has some similarities to the Covid19 study results. Grey and white matter differences in Chronic Fatigue Syndrome – A voxel-based morphometry study, 2018, Finkelmeyer et al
Re-reading, one is right arcuate 'fasciculus abnormality' (FA) and the other is fractional anisotropy (FA), so totally different. My bad.