Cerebrospinal fluid pleocytosis in multiple sclerosis patients with lesions showing reduced diffusion

In multiple sclerosis (MS) occasionally acute lesions show a reduced apparent diffusion coefficient (ADC) on magnetic resonance imaging (MRI); however, the underlying mechanism of this phenomenon is not known. We compared cerebrospinal fluid (CSF) findings with diffusion MRI signal characteristics of acute lesions in 25 patients with MS or a clinically isolated syndrome (CIS) later confirmed as MS. In nine of 25 patients investigated between days 1 and 4 after symptom onset, a reduced intralesional ADC value (–15% to −51%) was accompanied by a marked CSF pleocytosis (11–46 leukocytes/µl). Our results suggest that ADC reduction in acute MS lesions is a phenomenon that is possibly related to an aggressive inflammatory milieu as indirectly indicated by CSF pleocytosis. Furthermore, the ADC reduction and CSF pleocytosis were observed only early after symptom onset, which suggests that both are typically early and transient phenomena.