犬貓遺傳資訊站

 本文由 泡泡拔 翻譯於PWCCA網站 http://www.caninegeneticdiseases.net/dm/index.html

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 圖為美國有柯基DM病例的各州

 什麼是退化性脊髓神經病變(DM)?

Degenerative myelopathy (DM) is a progressive disease of the spinal cord in older dogs. The breeds most commonly affected include German Shepherds, Welsh Corgis, Irish Setters, and Chesapeake Bay Retrievers. The disease has an insidious onset typically around 9-11 years of age. It begins with ataxia: a loss of coordination in the hind limbs. The affected dog will wobble when walking, knuckle over or drag their feet, and may cross the feet. As the disease progresses, the limbs become weak and the dog begins to buckle at the knees and have difficulty standing. The weakness gets progressively worse until the dog is unable to walk. They may ultimately lose continence and function in the front limbs.

退化性脊髓神經病變(DM)，是一種漸 進性的脊髓病變，通常發生在年紀較大的犬隻身上。最常受到這個疾病影響的犬種，包含了德國牧羊犬、威爾斯科基犬、愛爾蘭獵犬與奇沙比克拾獵犬。這個疾病總在不知不覺中開始發病，發病的年齡一般來說在9~11歲之間。一開始犬隻會出現“運動失調”的病徵：喪失後肢的協調能力。患病的犬隻在走路時，會因不穩而 搖晃、下跪或拖行他們的後腳，也可能呈現交叉步伐。隨著病情加重，後肢會變得無力，犬隻只好用膝蓋去支撐，而且連站立都會顯得困難。後肢的衰弱會漸漸地愈來愈嚴重，直到狗狗無法行走。有時候他們甚至會連前肢都完全無法控制，而失去功能。

 

因為脊髓病變，所以大腦無法將命令送給後肢，後肢也無法將感覺送給大腦!

What causes DM?  造成退化性脊髓病變的原因?  

The exact cause of DM is unknown. Genetics probably plays an important role in the disease since it is common only in certain breeds of dogs and follows a stereotyped pattern. Various infectious, immune mediated, and nutritional theories have been investigated, but no definitive cause has been found.

究竟是什麼原因造成DM，目前還不清楚。遺傳也許在這個疾病扮演了重要的角色，因為他通常只發生在特定的品種，而且有一定的規律。有許多不同的感染源、免疫調控和營養理論都有被拿來研究過，但還是沒有辦法找到明確的致病原因。

We do know that the disease begins with the spinal cord in the thoracic (chest) area. If we look under the microscope at that area of the cord from a dog who has died from DM, we see degeneration of the white matter of the spinal cord. The white matter contains the fibers that transmit movement commands from the brain to the limbs and sensory information from the limbs to the brain. This degeneration consists of both demyelination (stripping away the insulation of these fibers) and axonal loss (loss of the fibers themselves).

目前可以確定的是，這個疾病一開始是在胸椎附近發生問題。如果死於DM的犬隻，把他胸椎的這個區域放在顯微鏡下觀察，可以發現脊髓的白質有退化的跡象。所謂的白質，裡面包含了神經纖維，功用為傳遞大腦的動作指令給後肢，同時也可以傳遞後肢的感覺給大腦。這些觀察到的退化跡象，包含了神經的去髓鞘化（就像電線的外皮被剝掉了，容易短路）與神經軸突的喪失（神經傳出訊號的一端不見了）。  

How is DM diagnosed?  如 何診斷DM?

DM is a diagnosis of elimination. That is we look for other causes of the weakness and when we have ruled them out, we end up with a tentative diagnosis of DM. The only way to confirm that suspicion, however, is to examine the spinal cord under the microscope when a necropsy (post-mortem exam) is performed. There are characteristic degenerative changes in the spinal cord, which tell us this is DM and not some other spinal cord disease.

DM的診斷必需藉助排除法。當我們想要找到造成他們後腿衰弱的原因時，我們必須把可能的因素一項一項排除，最後會得到一個暫時的診斷。不過要進一步確認病因，唯一的方法只有等狗狗過世後，利用顯微鏡來檢驗他們的脊髓。從顯微鏡下可以看到脊髓會有一些退化性的病徵，這些變化可以告訴我們狗狗得到的疾病是DM，或是其它的脊髓相關疾病。

What else can cause similar symptoms? 有什麼其它的因素可能造成類 似的徵狀?   

Any disease that affects the dog's spinal cord can cause similar signs of loss of coordination and weakness. Since many of these diseases can be treated effectively, it is important to pursue the tests necessary to be sure that the dog doesn't have one of these diseases. The most common cause of hind limb weakness is herniated intervertebral disks (slipped disks). The disks are shock-absorbers between the bones of the back. When they herniate, they can cause pressure on the spinal cord and weakness or paralysis. All of the short-legged dogs (Welsh Corgi, Dachshund, Basset Hound, etc.) are prone to slipped disks. A slipped disk can usually be detected with special X-rays of the spine (myelogram), but sometimes more advanced studies such as a CT or MRI scan are necessary. Even dogs with severely slipped disks can often be helped with surgery if diagnosed early.

任何對犬隻脊髓造成影響的疾病，都有可能造成後肢協調能力的喪失 或衰弱。因為許多這一類的疾病都可以有效的被治療，所以要確認是否患有DM，利用各種測試，來確認犬隻並不是得到這其些它種類的脊髓疾病，是相當重要且必須的。最常見到，造成後肢衰弱的原因是椎間盤突出。椎間盤的功能是在背部脊椎的骨頭之間，產生避震的效果，所以當椎間盤突出 時，會對脊髓產生壓力，而造成後肢衰弱或癱瘓。所有的短腿狗（威爾斯科基、臘腸、巴薩犬……等），都有比較 高的傾向得到椎間盤突出。椎 間盤突出通常可以利用脊髓的X光檢查檢測出來，不過有時候會需要更先進的檢查技術，像是核磁共振或斷層掃瞄。即使犬隻患有嚴重的椎間盤突出，如果能在早 期診斷出來，通常可以藉由手術來給予有效的治療。

Infections of the spinal cord can also cause weakness or paralysis. A spinal tap, usually taken at the time the myelogram is performed, can help detect inflammation of the spinal cord. Other diseases we consider include tumors, cysts, injuries and strokes. The combination of myelogram, spinal tap, and possibly CT or MRI allow us to diagnose most of these diseases. 

脊髓的感染也可能造成後肢衰弱或癱瘓。脊椎穿刺，通常會在照脊椎X光的同時，也一起做穿刺採樣，這可以幫忙檢測脊髓是否受到感染。其它我們可能考慮的疾病，包含腫 瘤、囊腫、脊髓損傷與中風。結合脊椎X光檢查、脊髓穿刺，或許再加上電腦斷層掃瞄與核磁共振，將可以讓我們診斷出大部分的脊髓相關疾 病。

 
 利用x光顯影來做檢查 

如何治療DM?

There are no treatments that have been clearly shown to stop or slow the progression of the disease. There are a number of approaches that have been tried, and we continue to look for new treatments. However, the outlook for a dog with DM is still grave. Things that can improve the quality of life for the dog include good nursing care, physical therapy, pressure sore prevention, aggressive treatment of urinary infections, and sometimes carts or harnesses to improve mobility. For information about suppliers of these aids, click HERE.

到目前為止，還沒有一種明確的治療方法，可以停止或減緩DM的惡化。有許多的方法都被嘗試過用來治療DM，而我們也還在不斷尋找新的治療方式。不過對於DM這個疾病的展望，我們仍然抱著嚴肅保守的態度。我們還是可以做一些事情，來增進DM狗狗的生活品質，像是妥善的照護、物理治療、壓力疼痛的預防、積極的治療尿路感染，有時候可以用推車或提帶來增加他們的活動能力。

What is the Degenerative Myelopathy Project? 什麼是DM計畫?

The Degenerative Myelopathy Project is a collaboration between investigators in Veterinary Schools at four Universities: Texas A&M, Missouri,Ohio State and North Carolina State funded by the Pembroke Welsh Corgi Club of America and the AKC Canine Health Foundation. Under the leadership of Dr. Joan Coates, each school brings a different set of strengths to bear on the problem. The aims of the project are to 1) characterize the disease in Pembroke Welsh Corgis, 2) test theories about the cause of the disease, 3) estimate the incidence in the breed, and 4) collect DNA and pedigree information for genetic studies.

DM計畫是由四所大學獸醫學院的科學家們所共同合作，包括：德州A&M大學、密蘇理大學、俄核俄 州大與北卡羅來那州大學，此計畫由美國潘布魯克威爾斯科基犬協會(PWCCA)與美國育犬協會(AKC)健康基金會所共同資助。本計畫由Joan Coates博士領導，每個學校各自著力於不同的部分，本計畫的目標有四個：1) 找出DM在科基犬中的各種特性，2)測試各種試圖解釋病因的理論，3)評估各品種DM的發生率，4)收集DNA與族譜資訊，以用來做遺傳研究。