馬爾濟斯與吉娃娃類奇亞里畸形/脊髓空洞化之型態學分析與症狀盛行率

Abstract

脊髓空洞症（syringomyelia，簡稱SM），為脊髓實質出現液體填充的空洞，會造成神經損傷，進而引發神經性疼痛、神經功能障礙等症狀。隨著磁振造影（magnetic resonance imaging，簡稱MRI）技術的普及，小型、玩具犬種診斷為SM的狀況逐漸增加。造成SM形成最常見的原因為類奇亞里畸形（Chiari-like malformation，簡稱CM）。此研究以回溯性方式，評估臺灣馬爾濟斯與吉娃娃具症狀CM、SM盛行率，並評估兩犬種中顱頸區域型態與SM之間的關連性。 本研究收集2008年至2017年期間於臺大動物醫院就診並進行頭頸MRI檢查的犬隻，記錄其犬種、症狀與MRI影像，並排除有顱內壓增加相關證據的病例。於MRI T2權重影像記錄各測量數值：顱後窩（caudal cranial fossa）三角面積、basion-occipital crest連線長度、枕骨大孔高度、顱頸關節（craniocervical junction）比例（顱頸關節與顱骨高度比值）、basion-atlas連線、obex位置（obex至枕骨大孔垂直距離）、延髓角度（延髓腹側與背側邊界夾角）、延髓kinking （medullary kinking，簡稱MK）指數、背側壓迫（dorsal compression，簡稱DC）指數以及寰樞帶（atlantoaxial band）壓迫分級。亦分析2008年至2017年期間所有至臺大動物醫院就診之犬隻病例數量與品種，計算具CM、SM臨床症狀犬隻之盛行率。 本院馬爾濟斯與吉娃娃具症狀CM、SM盛行率分別為0.06%與0.08%，47例馬爾濟斯MRI影像分析顯示顱後窩三角面積、obex位置與寰樞帶壓迫分級皆與SM嚴重程度有顯著關連性；在19例吉娃娃MRI影像分析中，脊椎型態相關測量（DC指數與寰樞帶壓迫分級）與SM嚴重程度有顯著關連性。 研究中，兩犬種具症狀CM、SM盛行率皆大於研究中全品種的盛行率，強調了兩犬種，尤其是吉娃娃，可能為此疾病的好發犬種。馬爾濟斯MRI影像分析結果發現患有SM病例的顱後窩減小，顯示出因短吻化導致顱後窩容積減小可能是此犬種形成SM的重要因子。此外，分析結果亦顯示前頸椎（尤其寰樞帶）的壓迫，在兩犬種中皆是SM形成的重要因子。未來研究方向包括增加樣本數，以及長期追蹤各測量數值的變化與SM進展，以進一步評估其各測量數值預測將來SM形成的效果。

Syringomyelia (SM) is a condition characterized by fluid filled cavities within spinal cord, resulting spinal cord damage, neuropathic pain and neurological deficits. The most common cause of SM in the dog is Chiari-like malformation (CM). This study aims to evaluate the prevalence of symptomatic CM/SM in Maltese and Chihuahua in Taiwan, and the relationship between cervicocranial morphology and SM in these breeds. Medical record of dogs admitted to National Taiwan University Veterinary Hospital between 2008 and 2017 were searched for dogs with MRI findings suggestive of CM+/-SM. Following data were collected, including age, breed, gender, clinical signs, MRI findings and diagnosis. Dogs with imaging evidence of increased intracranial pressure were excluded. The following parameters were measured on MRI T2W images: caudal cranial fossa (CCF) triangle area, basion-occipital crest distance, foramen magnum height, craniocervical junction (CCJ) ratio (CCJ height to CCF height ratio), basion-atlas distance, obex-foramen magnum distance, medullary angle (angle between ventral and caudal edge of medulla oblongata), medullary kinking (MK) index, dorsal compression (DC) index and atlantoaxial band compression grading. In addition, canine caseload with breed information over the same period of time was also analyzed for the prevelance study in symptomatic CM+/-SM dogs. The prevalence of symptomatic CM/SM is 0.06% and 0.08% in Maltese and Chihuahua, respecctively. In 47 Maltese dogs with CM/SM on MRI, caudal cranial fossa (CCF) cross-section area, obex-foramen magnum distance and atlantoaxial band compression were associated with the severity of SM. In 19 Chihuahuas, measurements of spinal morphology (medullary kinking and dorsal compression index, atlantoaxial band compression) were associated with SM severity. The prevalence of symptomatic CM/SM in Maltese and Chihuahua is higher than the prevalence in all breeds in this study. The cervicocranial morphometric analysis indicates decreased CCF volume and compensatively increased cranium height caused by brachycephalicism may be important factors in SM formation in Maltese. The data also emphasizes the role of CSF flow alteration in SM formation in both Maltese and Chihuahua. Future work should include larger sample size and longitudinal study to evaluate efficiency of these measurements as predictors of SM progression.