影像醫學於小動物神經醫學中之角色：從診斷到治療決策

Abstract

影像醫學工具在小動物神經領域扮演了相當重要的角色。雖然磁振造影所提供的軟組織細節，大幅提升了小動物神經醫學的境界，但放射線學仍是極具價值的影像工具，可提供快速及全面的初步評估。本論文描述三項臨床研究，以呈現影像醫學在獸醫神經臨床醫學中的重要與多樣性。 先天性寰樞椎不穩定（atlantoaxial instability）是一種好發於小型犬的疾病。儘管進階影像，如電腦斷層以及磁振造影，能提供此疾病的許多影像細節，X光仍是診斷此疾病的重要影像工具，也仍是現今小動物醫療現場最普及的影像設備。研究一旨在重新評估客觀的X光影像測量方法，於診斷小型犬寰樞椎不穩定疾病的應用價值。以經磁振造影診斷為寰樞椎不穩定疾病的10例特定品種犬隻，以及經磁振造影排除寰樞椎不穩定疾病的26例特定品種犬隻作為研究對象。藉由比較其屈曲、非屈曲側照以及腹背照X光影像，試圖找出最佳參數。經統計分析，非屈曲側照影像上的寰樞椎前端邊界距離與寰樞椎角度，以及腹背照影像上的齒突長度，具有極佳的鑑別力。此研究亦探討合併多項參數並運用連續三分法分析，協助診斷寰樞椎不穩定之可行性。分別以100%敏感度與100%特異度作為切點，將研究對象分為「診斷為患病」、「排除此疾病」或「無法判斷」。以單一參數進行三分法分析時，三種參數個別都能達到100%準確率，但歸類在「無法判斷」的犬隻比例高達31-47%。以齒突長度、寰樞椎前端邊界距離、寰樞椎角度的順序，進行連續三分法分析後，可大幅減少「無法判斷」族群的比例，同時保有100%的準確率。另以19例特定品種犬隻作為驗證群體，經此診斷方式分析後，正確判斷為「診斷為患病」或「排除此疾病」的準確率為100%，有5%犬隻歸類為「無法判斷」。此研究結果顯示，依腹背照X光影像的齒突長度、側照X光的寰樞椎前端邊界距離與側照上寰樞椎角度的順序，運用此研究歸納的切點數值與連續三分法分析，可協助診斷特定品種犬隻的寰樞椎不穩定疾病，同時也協助臨床獸醫師挑選極需進行進階影像檢查的病患。 研究二旨在描述因劣質商品化乾飼料，導致臺灣爆發貓硫胺素（維生素B1）缺乏症的事件，其臨床病程、神經症狀及磁振造影檢查所發現的異常，以及恢復情形。在此次事件中，磁振造影在區別診斷的過程扮演了關鍵性角色，後續再依據分析乾飼料中硫胺素含量，而得以確診。本研究共分析17例病患資料。大多數貓隻在出現急性神經症狀之前，表現出非特異的臨床症狀，包括厭食、倦怠或嘔吐。值得注意的是，前庭功能異常是最普遍的症狀（94％），且大多數患貓呈現雙側前庭症狀；其他神經症狀，包括異常的意識狀態（76％），失明（59％）和癲癇（59％）。有6例病患進行了腦部磁振造影檢查，其中5例呈現異常；另1例病患在已接受硫胺素補充治療後，因神經症狀仍未改善而進行腦部磁振造影檢查，但影像上並無發現異常。開始治療後，倖存的患貓症狀大多於二週內大幅改善至僅呈現輕微神經症狀或無症狀。前述腦部磁振造影無異常的病例，則於治療後6個月內緩慢恢復。初期有癲癇症狀的患貓，在整體病情穩定後，大多能停止使用抗癲癇藥且無癲癇復發。本研究確認了商品化乾飼料的製程或者保存瑕疵，會導致貓硫胺素缺乏症。當貓呈現前庭症狀、意識狀態改變與癲癇時，臨床獸醫師應將硫胺素缺乏症列為鑑別診斷之一。磁振造影在此疾病的診斷過程至關重要，但磁振造影影像沒有異常並無法完全排除此項疾病。若盡速接受治療，大多數患貓能迅速康復且預後良好。 在研究三中，磁振造影除了協助診斷患犬目前罹患的疾病，也提供了因先前椎間盤疾病而導致慢性脊髓傷害的資訊。本研究欲評估慢性椎間盤疾病是否會影響近期發生的椎間盤脫出（extrusion）或突出（protrusion）術後的恢復。神經功能痊癒的定義為「術前無法行走的犬隻，術後恢復行走功能；術前仍能行走但步態異常的犬隻，術後步態明顯改善；術前僅呈現頸痛而無其他症狀者，術後頸痛消失。」首先，以符合下列條件之40例犬隻為研究對象，分析此族群的術後神經功能恢復情形與預後因子。納入條件為呈現急性頸部神經症狀的犬隻，其磁振造影影像呈現頸部多處椎間盤脫出或突出，以腹側開槽減壓手術治療單一急性脫出或突出的椎間盤，並有完整的後續臨床追蹤紀錄。其次，分析23例急性頸部神經症狀，磁振造影顯示頸部單一急性椎間盤脫出的犬隻，進行腹側開槽減壓手術後的神經功能恢復情形。本研究亦比較上述二種族群之術後恢復狀況。研究結果顯示，多處椎間盤疾病的患犬，術後30日時有80%的犬隻神經功能痊癒，最終痊癒率為97.5%，中位痊癒時間為7天；預後因子分析方面，椎間盤脫出或突出的總數，是否有椎間盤疾病造成嚴重脊髓壓迫，以及造成嚴重脊髓壓迫的椎間盤脫出或突出之總數，皆不影響多處椎間盤疾病犬隻之術後30日時之痊癒率。與單一椎間盤疾病犬隻進行比較，二者之30日痊癒率、最終痊癒率、所需痊癒時間皆相似。將所有研究對象依椎間盤脫出或突出之總數分組，分為單一椎間盤疾病、二處椎間盤疾病、三處或三處以上椎間盤疾病，三組間的30日痊癒率、最終痊癒率、所需痊癒時間皆無差異。依以上結果推論，當犬隻呈現急性頸部神經症狀但影像檢查顯示多處椎間盤疾病壓迫脊髓時，若能辨識出近期脫出或突出的單一椎間盤位置，只針對此椎間盤進行腹側開槽減壓手術是種可行的治療策略。 上述三項研究呈現了影像工具所提供的結構與型態資訊，顯示影像醫學在臨床獸醫學上的重要性。然而，即使影像工具在診查過程中扮演了關鍵要角，仍需配合影像以外的其他檢查工具才能確診。除了結構與型態，人類臨床醫學上亦利用數種影像工具或技術間接評估神經系統的功能。未來研究若能結合這些評估神經功能的影像工具及技術，勢必能讓小動物臨床神經醫學更往前邁進一大步。

Imaging in small animal neurology can serve multiple essential functions. The exceptional soft tissue details provided by magnetic resonance imaging (MRI) have revolutionized our comprehension of small animal neurology. However, radiography continues to be a valuable tool for quick initial assessment. This thesis outlines three clinical studies that illustrate the multifaceted roles of neuroimaging in veterinary medicine. In study one, radiography’s diagnostic performance for atlantoaxial instability (AAI) in small-breed dogs was re-evaluated using objective radiographic measurements. Optimal parameters for AAI were determined by simultaneously evaluating flexed and non-flexed lateral radiographs and ventrodorsal radiographs from 10 MRI-diagnosed AAI dogs and 26 control dogs. Cranial border distance and C1-C2 angle on non-flexed radiographs, along with dens length on ventrodorsal radiographs, showed outstanding discriminatory capability. The potential of using serial trichotomization with multiple parameters was investigated. By applying cutoff values for 100% sensitivity and specificity, dogs were categorized into AAI diagnosed, ruled-out, or indeterminate. The accuracy rate was 100% for each parameter. However, 31-47% of dogs were classified as indeterminate. Serial trichotomization in the order of dens length, cranial border distance, and C1-C2 angle reduced the number of indeterminate cases while maintaining accuracy. This method was tested on 19 new subjects. Similarly, high accuracy (100%) with a small uncertainty zone (5%) was observed in the validation cohort. Using these cutoff values and applying serial trichotomization in the order of dens length, cranial border distance, and C1-C2 angle can help diagnose AAI in specific canine breeds and determine which patients require advanced imaging for an accurate diagnosis. Study two aimed to determine the progression of feline thiamine deficiency (TD) associated with defective dry food, its connection with neurological signs and MRI findings, and long-term outcomes. MRI served as a crucial diagnostic tool in this outbreak. Clinical records of 17 cats with TD due to defective dry food were analyzed. Most cats exhibited non-specific signs before acute neurological symptoms, including anorexia, lethargy, or vomiting. Notably, vestibular signs were prevalent (94%), and most had bilateral dysfunction. Other common neurological signs included altered mentation (76%), blindness (59%) and seizures (59%). MRI abnormalities were found in five out of six cats. MRI showed no abnormalities in one cat with ongoing severe neurological signs despite treatment. Most surviving cats recovered within two weeks, with absent or minimal neurological signs. One cat recovered slowly over six months. Seizure-free outcomes were common among cats with initial seizures. This study highlights the link between feline TD and defective dry food, emphasizing the need to consider this diagnosis in cats presenting with vestibular signs, altered mentation, blindness, and seizures. MRI plays a valuable role in diagnosis, but unremarkable MRI examination post-thiamine supplementation does not exclude the diagnosis. Prompt treatment typically results in a rapid and complete recovery for most cats. In study three, MRI not only diagnosed the current disease but also revealed information about previous chronic spinal cord injuries from prior disc disease. The study evaluated how pre-existing disc disease influenced the recovery outcomes of recent intervertebral disc extrusion/protrusion. The study first investigated prognostic factors in 40 dogs with multiple sites of cervical disc extrusion or protrusion on MRI who underwent ventral slot decompression (VSD) for the most recent acute disc issue. Results were then compared to those of 23 dogs with single disc extrusion treated with VSD. For dogs with an acute presentation but diagnosed with multiple cervical disc diseases, the 30-day and overall recovery rates were 80 and 97.5%, respectively, with a median recovery time of seven days. The number of affected discs and the presence and number of discs causing severe spinal compression did not significantly affect the 30-day outcome. The recovery times and outcomes were similar compared to the 23 dogs with a single disc extrusion treated surgically. The total number of affected discs did not correlate with recovery time or outcomes. In conclusion, if an acute disc issue could be identified, VSD targeting the single acute disc is a viable management approach for dogs with an acute presentation but diagnosed with multiple sites of spinal cord compression due to disc disease. The preceding studies underscore the pivotal role of imaging in offering structural information. Nevertheless, it is crucial to remember that, although imaging plays a vital role in diagnostic investigations in many circumstances, the diagnosis is reached by combining all investigation results or is confirmed by other further tests. In humans, several other imaging methods have also been successfully employed to assess the functional aspects of the nervous system. Future studies incorporating these imaging modalities and techniques will likely propel our understanding of small animal neurology to new heights.