Multiple sclerosis and fatigue: A review on the contribution of inflammation and immune-mediated neurodegeneration

Multiple sclerosis (MS) is an immune mediated disease of the central nervous system (CNS) and the leading cause of non-traumatic disability among young and middle-aged adults in the western world. One of its most prevalent and debilitating symptoms is fatigue. Despite the general acceptance of the idea of an immune pathogenesis of MS itself, the role of autoimmunity in the course of MS-fatigue is a matter of debate. Both immune-related processes (acute inflammation, chronic inflammation, immune-mediated neurodegeneration, immune-mediated alterations of endocrine functions related to fatigue) and presumably non-immune-mediated disturbances and factors (sleep disturbances, depression, cognitive alterations, chronic infections, adverse effects of medications) contribute to the clinical picture. Data from in vitro and animal experiments has provided evidence for a role of cytokines as IL-1 and TNF-alpha. This association could not be verified directly in blood samples from humans whereas whole blood stimulation protocols gave some indirect evidence for a role of cytokines in MS-fatigue. MRI being able to detect acute and chronic immune mediated damage to the CNS could depict that global atrophy of gray or white matter does not correlate with fatigue. Rather, distinctive clusters of lesions and atrophy at different locations, mostly bifrontal or in subcortical structures, correlate specifically with fatigue.Regardless of the difficulties in pinpointing the immunogenesis of MS-fatigue, an important role of autoimmunity is strongly supported by an indirect route: A growing amount of data shows that the highly effective immunotherapeutics which have been introduced to MS-treatment over the last years effectively and sustainably stabilize and ameliorate fatigue in parallel to their dampening effects on the neuroinflammatory process. This review summarizes the existing data on the relation between inflammation, patterns of CNS-lesions and the effects of immunotherapeutics on MS-fatigue.