19 General introduction Table 3. 2017 McDonald Criteria for diagnosis of Multiple Sclerosis Clinical presentation What additional data is needed for anMS diagnosis? Two or more relapses AND EITHER objective clinical evidence of two or more lesions OR objective clinical evidence of one lesion together with reasonable historical evidence of a previous relapse None Two or more relapses; objective clinical evidence of one lesion (shows DIT) Dissemination in space shown by: One or more MRI detected lesions typical of MS OR A further relapse showing damage to another part of the CNS One relapse; objective clinical evidence of two or more lesions (shows DIS) Dissemination in time shown by: Oligoclonal bands OR MRI evidence of a new lesion since a previous scan OR A further relapse One attack/relapse; objective clinical evidence of one lesion (known as ‘clinically isolated syndrome’) Dissemination in space shown by: One or more MRI detected lesions typical of MS OR A further relapse showing activity in another part of the CNS Dissemination in time shown by: Oligoclonal bands OR MRI showing new lesions since a previous scan OR A further relapse Insidious neurological progression suggestive of multiple sclerosis (typical for primary progressive MS) Continued progression for one year (from previous symptoms or by ongoing observation) plus any two of: One or more MRI detected lesions in the brain typical of MS, Two or more MRI detected lesions in the spinal cord, Oligoclonal bands in the spinal fluid Abbreviations: CNS, central nervous system; DIS, dissemination in space; DIT, dissemination in time; MRI, magnetic resonance imaging; MS, multiple sclerosis. Neuropathology The pathology of MS is primarily based on the presence of microglia and macrophages, the loss of myelin, the degree of astrogliosis and neuronal and synaptic loss (Figure 3). Histopathological, the lesions are classified as preactive, active, chronic active, or inactive. Upon histopathological examination, preactive lesions are classified as clustering microglia in the normal appearing white matter (NAWM). In the NAWM there is no myelin damage, no astrogliosis and only rarely foamy macrophages are observed169. The preactive lesion is a relatively new description in neuropathology and the term suggests it could be the start of the classical active lesions that are commonly described. However, the discrepancy between number of preactive lesions and the relatively lower number of active lesions suggest that a significant amount of preactive lesions do not develop into active lesions. Active lesions are characterised by myelin loss and damage, the presence of foamy macrophages and microglia, periventricular infiltrates filled with cells of the peripheral immune system, mainly lymphocytes169. Chronic active lesions are characterised by a rim of foamy macrophages around the area of demyelination, the centre of chronic active lesions shows signs of astrogliosis and hypertrophy and is hypocellular169. Inactive lesions show signs of severe myelin damage, hypertrophic astrocytes and is characterised by hypocellularity169. In inactive
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