A 27-year-old man, receiving his 27th dose of natalizumab monotherapy for multiple sclerosis (MS), tested positive for the anti-JCV (John Cunningham virus) antibody with a low index (0.23). Five days after his 30th dose, he developed horizontal diplopia. An MR scan of the brain identified a tumefactive lesion in the right middle cerebellar peduncle, with no enhancement, and was interpreted as an MS attack (figure 1). He received two cycles of intravenous methylprednisolone but progressed with dysarthria and tetraplegia. Less than 3 months later, MR scan of the brain showed progressive expansion of the previous lesion, affecting the pons, both the right and left cerebellar peduncles, and the cerebellum (figure 2). Cerebrospinal fluid (CSF) analysis showed a strongly positive JCV PCR (>1 300 000 DNA copies/mL). Pembrolizumab was administered (2 mg/kg body weight intravenously, once) but no clinical response at 6-month follow-up (Expanded Disability Status Scale - EDSS 9.5). Figure 1 MR scan of the brain: (A) axial fluid attenuated inversion recovery (FLAIR) and (B) T2-weighted image, before onset of diplopia showing typical periventricular and deep white matter multiple sclerosis lesions (arrows) and normal right middle …

中文翻译：

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孤立于脑干和小脑的进行性多灶性白质脑病

一名 27 岁男性接受第 27 剂那他珠单抗单药治疗多发性硬化症 (MS)，其抗 JCV（约翰坎宁安病毒）抗体检测呈阳性，指数较低 (0.23)。第 30 次注射后五天，他出现水平复视。大脑 MR 扫描发现右侧小脑中脚有一个肿胀性病变，没有增强，被解释为多发性硬化症发作（图 1）。他接受了两个周期的静脉注射甲基泼尼松龙，但出现构音障碍和四肢瘫痪。不到 3 个月后，大脑 MR 扫描显示先前病变逐渐扩大，影响到脑桥、左右小脑脚以及小脑（图 2）。脑脊液 (CSF) 分析显示 JCV PCR 呈强阳性（>1 300 000 DNA 拷贝/mL）。给予派姆单抗（2 mg/kg 体重静脉注射，一次），但在 6 个月随访时没有临床反应（扩展残疾状态量表 - EDSS 9.5）。图 1 大脑 MR 扫描：(A) 轴向液体衰减反转恢复 (FLAIR) 和 (B) T2 加权图像，复视发生前显示典型的脑室周围和深部白质多发性硬化症病变（箭头）和正常的右中......