Humoral and cellular immune response within the CSF- (and putatively central nervous system (CNS)-) compartment. The initial cerebral MRI about half a year after symptom onset was unremarkable (A, FLAIR-weighted images, C, T2 weighted images). Two years after symptom onset a pronounced cerebellar atrophy, especially of the medial parts of the hemispheres and the vermis, was evident (B, FLAIR-weighted images, D, T2 weighted images), and cerebral FDG-PET showed pronounced hypometabolism of the whole cerebellum (E, arrow). A computed tomography (CT)-scan of the chest showed a nodular lesion of the apical thymus (F, arrow). Flow-cytometry of the cerebrospinal fluid (G, lower panels; H, open red circles; CSF) as compared to the peripheral blood (G, upper panels; H, filled red circles; PB) and to a total of 17 healthy controls (H, filled and empty black circles) showed a low CD4/CD8 ratio together with increased fractions of activated HLA-DR+ CD4+ T cells and especially HLA-DR+ CD8+ T cells as well as CD19+ B cells and CD138+ plasma cells suggesting that both B cells and CD8+ T cells were preferentially recruited to and activated within the cerebrospinal fluid-compartment.