Degenerative Myelopathy
Degenerative myelopathy (DM), also known as chronic degenerative radiculomyelopathy (CDRM), is a disease affecting the spinal cord, resulting in slowly progressive hind limb weakness and paralysis. The symptoms result from degeneration of the white matter of the spinal cord. DM is similar to some of the forms of human amyotrophic lateral sclerosis (ALS) more commonly known as Lou Gehrig’s Disease.
The exact cause of DM is unknown. In its early stages, the symptoms of DM resemble those of osteoarthritis (arthritis), which often occurs secondary to hip dysplasia in many large breed dogs, making diagnosis challenging.
In later stages of the disease, the progressive weakness and ataxia (wobbling, stumbling) distinguish it from osteoarthritis of the hip joints. Other considerations for this condition include spinal injuries, spinal tumors, lumbosacral stenosis, fibrocartilaginous embolism, myasthenia gravis, and discospondylitis.
Early clinical signs include:
The condition is most common in middle-aged to older dogs, with a range from 4-14 years. It has been reported in young dogs on rare occasions.
Prior to a 2014 study, the cavalier King Charles spaniel was not believed to have a high prevalance rate for CDM. According to pevalence rates which were calculated on the number of dogs presented to veterinary teaching hospitals in North America between January 1990 and December 1999, CDM is most common in German shepherd dogs (prevalence rate 2.01%) and also common in Pembroke Welsh Corgis (prevalence rate 0.58%), boxers (prevalence rate 0.59%), Chesapeake Bay retrievers (prevalence rate 0.83%), Rhodesian ridgebacks (prevalence rate 0.74%) and collie (prevalence rate 0.38%), and less common in several other breeds, including the cavalier.
However, in that 2014 study, a mutation of the SOD1 (superoxide dismutase 1) emzyme has been identified in the cavalier King Charles spaniel. The exact frequency of this disease and approximate age of disease onset are unreported for the CKCS, but in that study, 37% out of 73 cavaliers tested were carriers of the mutation, and 49.3% were at-risk or affected. In that study, however, there is no indication as to how the 73 cavaliers were selected. These extremely high percentages are vastly different from objective breed-wide statistical studies, such as the UK study from 1990 to 1999, which showed the highest percentage of affected German shepherd dogs at 2.01%.
CDM has been determined to be an inherited neurologic disorder caused by a mutation of the SOD1 (superoxide dismutase 1) emzyme. The SOD1 mutation appears to cause a mis-folding of proteins, resulting in an accumulation of toxic by-products in the axon (nerve fibers which transmit information to different neurons). These toxic by–products disrupt axoplasmic flow, eventually destroying myelin and ultimately replacing normal axons with astrogliosis (an abnormal increase in the number of astrocytes due to the destruction of nearby neurons).
Interestingly, it appears that not all cavaliers carrying two copies of the SOD1 mutation will develop the disease. So, there is much more to be learned about this disorder in the CKCS.
The exact cause of DM is unknown. In its early stages, the symptoms of DM resemble those of osteoarthritis (arthritis), which often occurs secondary to hip dysplasia in many large breed dogs, making diagnosis challenging.
In later stages of the disease, the progressive weakness and ataxia (wobbling, stumbling) distinguish it from osteoarthritis of the hip joints. Other considerations for this condition include spinal injuries, spinal tumors, lumbosacral stenosis, fibrocartilaginous embolism, myasthenia gravis, and discospondylitis.
Early clinical signs include:
- The hind paws "knuckle" or turn under so that the dog walks on its knuckles, especially when turning.
- The dog's hindquarters appear to sway when standing still.
- The dog falls over easily when pushed from the side.
- The hind feet seem to scrape the ground when walking and sometimes the top surface of the feet become hairless and irritated from repeated trauma.
- The dog has difficulty getting up from a lying position.
The condition is most common in middle-aged to older dogs, with a range from 4-14 years. It has been reported in young dogs on rare occasions.
Prior to a 2014 study, the cavalier King Charles spaniel was not believed to have a high prevalance rate for CDM. According to pevalence rates which were calculated on the number of dogs presented to veterinary teaching hospitals in North America between January 1990 and December 1999, CDM is most common in German shepherd dogs (prevalence rate 2.01%) and also common in Pembroke Welsh Corgis (prevalence rate 0.58%), boxers (prevalence rate 0.59%), Chesapeake Bay retrievers (prevalence rate 0.83%), Rhodesian ridgebacks (prevalence rate 0.74%) and collie (prevalence rate 0.38%), and less common in several other breeds, including the cavalier.
However, in that 2014 study, a mutation of the SOD1 (superoxide dismutase 1) emzyme has been identified in the cavalier King Charles spaniel. The exact frequency of this disease and approximate age of disease onset are unreported for the CKCS, but in that study, 37% out of 73 cavaliers tested were carriers of the mutation, and 49.3% were at-risk or affected. In that study, however, there is no indication as to how the 73 cavaliers were selected. These extremely high percentages are vastly different from objective breed-wide statistical studies, such as the UK study from 1990 to 1999, which showed the highest percentage of affected German shepherd dogs at 2.01%.
CDM has been determined to be an inherited neurologic disorder caused by a mutation of the SOD1 (superoxide dismutase 1) emzyme. The SOD1 mutation appears to cause a mis-folding of proteins, resulting in an accumulation of toxic by-products in the axon (nerve fibers which transmit information to different neurons). These toxic by–products disrupt axoplasmic flow, eventually destroying myelin and ultimately replacing normal axons with astrogliosis (an abnormal increase in the number of astrocytes due to the destruction of nearby neurons).
Interestingly, it appears that not all cavaliers carrying two copies of the SOD1 mutation will develop the disease. So, there is much more to be learned about this disorder in the CKCS.
