In July, 2008, a 56-year-old man, with a medical history of hypertension, type 2 diabetes mellitus, and hypercholesterolemia and a cardiac catheterization, presented with a 3-month history of left-sided facial and lingual sensory loss. Subsequently, he developed gait ataxia, binocular horizontal diplopia, and dysarthria. A neurological examination revealed left-sided fifth and sixth nerve palsy and gait ataxia, and left-sided finger-nose and heel-shin tests revealed impaired coordinated movements of the upper and lower limbs, respectively. T2-weighted MRI of the brain showed multiple punctuate hyperintense lesions within the pons, cerebellum, and medial cerebellar peduncle that extended into the left mediofrontobasal region and the left frontal lobe and corpus callosum, with curvilinear gadolinium enhancement (Figure 1A). The results of MRI of the spine and of computed tomography of the thorax and abdomen were entirely normal. Cerebrospinal fluid samples revealed mild pleocytosis but no atypical or malignant cells, and no evidence for intrathecal IgG synthesis. Cerebrospinal fluid immunocytochemistry showed mainly T lymphocytes and, in the absence of B cells, no hint of B-cell monoclonality. The patient was treated with 1000 mg of intravenous methylprednisolone sodium succinate for 3 consecutive days, which lead to a substantial improvement of clinical symptoms, especially with regard to diplopia and facial hypoesthesia. In addition, the inflammatory changes detected in the brain on MRI scans regressed. However, 6 weeks later, his symptoms worsened, with increasing gait ataxia, diplopia, dysarthria, and aphasia and with a clinical examination now also showing a seventh nerve palsy, impaired coordination, and bipyramidal syndrome. The MRI scans revealed an increased number of punctuate and curvilinear gadolinium-enhanced hyperintense white matter lesions, mainly in the pons, cerebellum, and periventricular region (Figure 1B).