L'inflammation microscopique dans la sclérose en plaques : inflammation focale et inflammation diffuse

The basic hallmark of multiple sclerosis pathology is the focal demyelinated plaque; it is visible as a focal T2-hypersignal lesion on MRI and under microscopy perivenular mononuclear cells infiltrates are described associated with demyelination with partial axonal loss. In that focal lesion, lymphocytes and especially CD8+ T cells are well represented but B cells can be found, outnumbered by macrophages with myelin debris. MS is a an inflammatory demyelinating and degenerative chronic and evolving disease where a diffuse inflammation in the tissue is also described early but is more and more prominent over time. This diffuse inflammation in white and grey matter is trapped in the parenchyma without any evident disruption of the blood brain barrier. That chronic diffuse and trapped inflammation is characterized by a prominent activated microglia. Indeed, inflammation remains the key feature in relapsing remitting form as well as in secondary or primary progressive form of MS, and inflammation stay related to the demyelination and axonal loss parameters.