Figure 1 Sagittal postcontrast T1-weighted MRI
Sagittal postcontrast T1-weighted MRI shows diffuse enhancement of the arachnoid membrane and radices.

Figure 2 FDG-PET

Coronal (A), sagittal (B), and transversal (C) FDG-PET show only pathologic increased uptake in the spinal cord. The SUVmax
was calculated in different areas of the spinal cord according to the guidelines of the European Association of Nuclear Medicine and normalized to a glucose level of 5.0 (range 4.4–6.0)

         A 50-year-old man presented with progressive tetraparesis  and loss of vision. Inflammation and malignancy  were considered based on diffuse meningeal  enhancement on MRI (figure 1) and CSF content   (very high protein, mild pleocytosis, and low to normal  glucose). CSF cultures and cytologic examinations, including flow cytometry, were normal. FDG-PET showed increased uptake in the spinal cord and brain (figure 2), matching primary diffuse leptomeningeal gliomatosis (PDLG), leptomeningeal  carcinomatosis/lymphoma, or isolated CNS infection.  A temporal leptomeningeal-cortical biopsy confirmed PDLG.
Although rarely performed, FDG-PET in PDGL characteristically demonstrates increased uptake isolated to the CNS.

      男性，50岁，以进行性四肢瘫痪伴视力减退数月就诊。MRI检查提示脑膜和脊膜弥漫性增强信号（图）。脑脊液检查提示蛋白增高，轻度细胞增多和低糖。脑脊液培养和细胞学检查阴性。FDG-PET 显示脑和脊髓摄取明显增高（图2），提示弥漫性软脑膜胶质瘤病（PDLG）、淋巴瘤或孤立性中枢神经系统感染可能。软脑膜活检病理证实为PDLG。

                                               Neurology. 2013 Oct 15;81(16):e119-20. 

评论：​
    按月进展的神经系统疾病需高度怀疑肿瘤和感染，感染者多伴有发热等全身症状。脑脊液提示低糖多支持生物源性病变，包括细菌、真菌、结核和肿瘤，但也有少数例外，我们曾碰到一例脊髓SDAVF，其脑脊液糖低至0.7mmol/L以下。本例患者脑脊液糖低，高度支持生物源性病变。​
    临床上诊断本例病人的策略大致有二：要么一步到位直接行软脑膜或脊膜活检，通过病理明确病变性质；要么按感染性病变（多会考虑结核）先诊断性治疗，如若无效再考虑活检病理确诊。无论选择哪一种策略我认为都无可厚非，各有利弊。临床变化多端，总会有意外，只有在争取病人家属依从性的前提下坚持追查到底方能水落石出。​

知识链接：神经科常用的PET显像有哪些？​
     PET在神经科常用的显像包括FDG、DAT、胆碱和蛋氨酸，FDG主要针对恶性肿瘤或活跃的炎症，DAT针对帕金森或帕金森综合征，胆碱和蛋氨酸主要针对胶质瘤。