The establishment of the experimental chronic compressive myelopathy and the mechanism of somatosensory-evoked potential's evaluation

Abstract

目的 建立新型大鼠脊髓慢性壓迫模型,進一步探討體感誘發電位(somatosensory evoked potential,SEP)對慢性壓迫性脊髓癥的診斷價值及其對應的病理生理改變.方法 15只大鼠經后路手術于頸椎管內植入吸水性聚氨酯膠片,植入體內會逐漸吸水脹大,形成對脊髓的慢性持續壓迫.術后6個月,對慢性壓迫脊髓進行SEP、影像學、組織學和組織化學檢測.結果 15只造模大鼠脊髓均出現側后方明顯壓迫性形態學改變,微焦點計算機斷層掃描顯示脊髓灰質和白質扭曲變形.9只表現為潛伏期延長和(或)波幅F降等SEP異常,SEP反應分為Ⅰ型6只、Ⅱa型5只、Ⅱ b型2只、Ⅲ型2只.正常和異常SEP的脊髓壓迫率差異無統計學意義(P>0.05).SEP反應異常的大鼠與反應正常者脊髓的組織學、組織化學比較,脊髓后索髓鞘染色顯著減少(Ⅱ a:106±12,Ⅰ:121±8,P=0.038),脊髓后索的對比劑密度差異有統計學意義(Ⅱ a:95±5,Ⅰ:87±6,P=0.042),而且后角內神經元也明顯較少[Ⅱ a:(25±8)/mm2,Ⅰ:(29± 6)/mm2 P>0.05];Ⅱ b型和Ⅲ型不僅脊髓后索髓鞘著色減少,灰質后角神經元密度只有(16±5)/mm2和(14±5)/mm2;均出現基質海綿樣變和靜脈擴張.結論 在慢性壓迫性脊髓癥發展過程中,SEP出現異常遲于形態學改變,但是反映了脊髓后索和后角神經元損傷的嚴重程度.為深入研究脊髓型頸椎病的病理生理機制和療效評估提供了良好的動物模型. Objective To explore the pathophysiological changes behind somatosensory evoked po-tential (SEP) defect and its diagnostic value in an established model of spinal cord chronic compression. Methods Total 15 rats were operated with implantation of a water-absorbing polymer sheet in cervical spinal canal, which expanded gradually to induce chronic compression to the spinal cord. At 6 months after surgery, SEP, radioiogical and pathohistological/istochemistry evaluations were done. Results Spinal cord in 15 rats showed significant morphological compressed deformity after chronic compression. It was also characterized by higher contrast intensity and distortion of gray matter and whiter matter under micro-CT e-valuations. SEP revealed that nine rats had prolonged latency and/or decreased amplitude. Based on their different SEP response, they were categorized into: type Ⅰ (n=6), type Ⅱa (n=5), type Ⅱb (n=2), type Ⅲ (n=2), and type Ⅳ (n=0). Compression ratio was not different between normal and abnormal SEP responses in the rats. Compared with the rats with normal SEP responses, the spinal cord of rats with normal SEP responses showed less myelin staining in white matter(Ⅱa: 106±12 vs.Ⅰ: 121±8; P=0.038), less contrast medium density in posterior dorsal column (Ⅱa: 95±5 vs. Ⅰ: 87±6; P=0.042), lower neuron density and cavitation in gray mat-ter[Ⅱa: (25±8)/mm2 vs. Ⅰ: (29±6)/mm2, P>0.05]. Less myelin staining in posterior column whiter matter could be seen in type Ⅱb and Ⅲ. Neuron density in posterior horn of gray matter were (16±5)/mm2 and (14± 5)/mm2 respectively. Histological cystic cavitations and sinusoidal dilation of veins were noted in spinal cord with significant distortion after compression. Conclusion SEP responses reflected the severity of spinal cord posterior tract and horn damage in chronic compressive injuries after gross appearance changes