Cerebral tumor and multiple sclerosis (MS) relapses can show overlapping clinical and magnetic resonance imaging features. In a previous study we observed in relapsing MS patients increased T-bet, pSTAT1, and pSTAT3 expressions in circulating mononuclear cells. During the data analysis we observed that T-bet, pSTAT1, and pSTAT3 expression was not increased in circulating mononuclear cells from a relapsing-remitting (RR)MS patient with recent onset of new neurological signs due to glioblastoma multiforme. In conclusion, our patient represents an exemplary case which suggests that T-bet, pSTAT1, and pSTAT3 expression in peripheral blood mononuclear cells (PBMCs) might be useful to differentiate MS relapses from other noninflammatory diseases.