Comparative Study Between Cognitive Phenotypes of Myalgic Encephalomyelitis/Chronic Fatigue Syndrome and Multiple Sclerosis.

: Cognitive impairments are one of the most common and disabling symptoms associated with myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS). Here, we address the possibility of a specific cognitive profile inherent to ME/CFS. Due to the occurrence of cognitive deficits, fatigue, and pain in both pathologies, multiple sclerosis (MS) is a relevant comparison model. For this purpose, we carried out a comparative study between cognitive profiles of patients with ME/CFS and patients suffering from MS. : In total, 40 ME/CFS and 40 MS patients were included. A complete screening of all cognitive functions was carried out through an extensive battery of tests routinely used in clinical practice. : ME/CFS and MS patients showed deficits in episodic memory retrieval, visual selective attention and reading speed. ME/CFS patients also elicited a lower level of performance than MS patients regarding consolidation. For both groups, levels of performance on these cognitive tests did not correlate with levels of fatigue, pain, and depression. : This study highlighted both similarities and differences in the cognitive profiles of ME/CFS and MS patients. While both groups exhibited deficits in episodic memory retrieval, visual selective attention, and reading speed, ME/CFS patients showed distinct impairment in consolidation processes. These cognitive deficits were not correlated with fatigue, pain, or depression, reinforcing the hypothesis of intrinsic cognitive dysfunction in ME/CFS. These findings define a specific cognitive phenotype for ME/CFS, which could improve diagnostic accuracy and therapeutic strategies. Future research, particularly in functional imaging, may elucidate the neurobiological mechanisms underlying these impairments.