Dissociation between histological and clinical signs of experimental auto-immune encephalomyelitis

Lewis rats show a rough correlation between clinical score and histological score of auto-immune encephalomyelitis (EAE). When animals with strong and comparable clinical EAE but with different genetic backgrounds are studied four weeks after immunization, they reveal histological changes that vary markedly according to the genetic set-up. When studied at the height of the EAE attack, also rats with a very low histological score at day 28 have marked histological changes. The results indicate that routine evaluation of EAE strength by histology at a time when the rats have recovered from paralysis may give quite misleading results in some rat strains or crosses, even though the method is good for the Lewis rat. It is suggested that the late histological score is more related to the presence of a relapsing EAE than to the disease activity in the first attack.