The distinct WM impairments between the PI-ME/CFS and GO-ME/CFS groups highlight the heterogeneity of ME/CFS. Interestingly, conventional clinical measures (SF-36, HADS, PSQI and BDS) did not differentiate between the two groups. This discrepancy calls into question the effectiveness of current clinical assessment tools for distinguishing ME/CFS subgroups and highlights the need for more sensitive instruments.