[Multiple sclerosis: one or several diseases?]

The various clinical courses of multiple sclerosis (relapsing-remitting, primary progressive, secondary progressive, progressive-relapsing) are likely related to different severity or distribution of the main lesions that constitute the plaques (inflammation, demyelination, axonal injury and loss, necrosis). They might lead to different therapeutic approaches. Some cases of the other clinico-radiological or clinico-pathological variants (pseudo-tumoral, concentric sclerosis of Baló, acute disseminate encephalomyelitis, Devic's neuromyelitis optica) obviously share similar mechanisms with multiple sclerosis. Other cases are, on the contrary, linked to different diseases. Do the variants of multiple sclerosis could be the consequence of different diseases? This is, today, a highly speculative conjecture. The prevalent hypothesis suggests that the clinico-pathological heterogeneity of multiple sclerosis is linked to the variability of the reaction of the nervous tissue to an initial injury. This different vulnerability, that depends on unknown factors, would explain the variants of the disease.