-Bobbie Mayer
There can be a lot of confusion about IVDD (intervertebral disk disease, aka IVD, disk rupture) and DM (Degenerative myelopathy) in both breeds of corgi. Here’s a quick primer on what they are what to look for , what to do, and prevention.
We don’t know the real incidence of either DM or IVDD in Cardigans or in Pembrokes. I can tell you from my experience with CorgiAid’s cart loan program that IVDD is much more common in Cardis than in Pems, and DM is much more c common in Pembrokes than in Cardis. But it is also true that there are misdiagnoses, and many dogs are never diagnosed at all.
IVDD has several types. Type I is the sudden spontaneous disk rupture, that is, the corgi “goes down”, from healthy and normal to possibly paralyzed within hours to days. It can be triggered by some activity or can happen overnight or during minimal movement, but it isn’t caused by what you did or didn’t do. The disk, which is a gel-filled cushion between the vertebrae, has calcified, the gel hardened and become brittle, and it is like an egg that instead of being hardboiled has the insides blown out and is ready to shatter. Except when it does the stuff inside is propelled with some force into the spinal cord, causing damage and swelling, which in turn causes paralysis. This often hits young, healthy corgis, usually between about 2 and 6 years of age, but can happen at any age. It probably has a genetic component, but the mode of inheritance isn’t known and there is no test for it. Often the dogs that get it are in great shape physically.
While being overweight and doing activities (like downstairs) are not causes of IVDD type I, they can make it harder if your dog ends up with rear end paralysis, as using a cart is difficult if the dog’s front end is arthritic or very heavy or both. A heavy front or tummy pulls the weight of the cart down onto your dog’s back or shoulders, and arthritis or lameness in the front makes this even worse.
Type II IVDD is the slow age-related degeneration of the disk. It can occur in any breed (not more common to dwarf dogs) and can mimic DM, in that the dog often goes down slowly and may show no outward signs of pain. This is probably the leading cause of misdiagnoses in corgis of both breeds. For example, Parker, a Pem, was diagnosed by several vets including specialists with DM. He was down in back and using a cart, showed no signs of pain, and had gone down gradually. But when the DM DNA test came out in 2008 his owner tested and found that he was a carrier. She started treating his infirmity as IVDD and he recovered his ability to walk. There are also blatant misdiagnoses, such as Flash, who went down suddenly but, because he was at risk for DM, got that diagnosis when he obviously had IVDD. I’ll explain both below and talk about how they can be differentiated.
DM usually hits corgis from 8 years of age and up and is caused by the disease attacking motor neurons in the spinal cord. It is the canine equivalent of ALS or Lou Gehrig’s disease. It is much less common in Cardigans than in Pems, and because research has targeted the more common disease in Pembrokes, we know much more about it in that breed. That does mean we know quite a bit less about it in Cardigans. There is a genetic test for DM which can tell you if your corgi is Clear, Carrier, or At Risk for DM. Your breeder may have been able to tell you this by parentage since the inheritance is known, or may have tested, but you can also send away for a DNA test for your pup if you don’t know. It isn’t 100% straightforward, though, as we don’t know what percent of At Risk corgis get DM and on rare occasions a Carrier may be able to get it. (This is extremely unlikely in Pems but due to the lower incidence in Cardigans it is hard to say how unlikely it is- but still much less likely than in At Risks.) A gene was recently found in Pems that codes for early onset of DM (8-11) vs late onset, but we don’t know yet if this is true for Cardis (though my guess is yes.) But breeding for Carrier and Clear should help reduce the incidence in both Cardigans and Pembrokes.
DM is diagnosed by a DNA test, and symptoms, and ruling out other causes. This includes an MRI or CT with contrast to rule out IVDD, so often is not done since these are expensive tests. Alternatively it can be diagnosed by examination of the spinal cord after death. You may hear that you MUST diagnose after death but I disagree with this- the characterization of the spinal cord in DM dogs was done based on the criteria of ruling out other causes by MRI or CT and progression of symptoms, and now with added DNA tests this is a sound diagnosis. But without the imaging, you really cannot know for sure at least until the disease progresses. X-rays may indicate disk disease but cannot be used to rule it out as they cannot image a bulging disk, just changes in the spacing between vertebrae and some degeneration of the disks.
Further complicating things, you cannot diagnose DM if disk disease is also present- but a corgi can have both. There is no pain with DM but you may not observe any pain with type II IVDD, either.
DM starts (as does IVDD in the slower onset) with subtle things, such as a change in gait, ticking jumps, and progresses to loss of proprioception, that is, your dog starts not to know where his feet are in space. This initially affects turning and standing and walking on slick floors, but ultimately the feet start to knuckle. Then the muscles start to weaken, and after 6-12 months the dog is no longer able to stand and needs to use a rear wheel cart. In another 12-24 months the disease progresses to the trunk and ultimately the front legs, and a four wheel cart may be needed. Incontinence in males usually starts sometime after the back legs go down, and in females may or may not happen. DM is always slow onset- there is no such thing as going down overnight with DM. But since IVDD can be slow onset as well, the progression to the front legs will ultimately tell you it is more likely DM.
One simple test that may help differentiate the two is to give a few weeks trial of an NSAID like Rimadyl. The dog with IVDD may get better, the dog with DM won’t. It can’t rule out IVDD but may tell you that it is not DM. Steroids may do the same, but are not a great idea in the event it is DM since they cause muscle atrophy over time, and the same is true for prolonged crate rest (though a short trial of a few days to see if symptoms go away or get better may be worthwhile.) (Since both NSAIDs and steroids can affect your dog’s liver, and older dogs often have early liver disease, it is important to do bloodwork to make sure your dog can tolerate these medications.)
Several other distinctions may help. Pain perception should be fully intact early in DM but may be diminished in IVDD. Incontinence rarely occurs early in DM and may in IVDD. (But other causes of incontinence may be present, such as spay incontinence in older spayed females, or UTIs.)
In any case, type II IVDD is generally treated much like DM, with the use of medications to reduce inflammation and treat pain being the major difference.
DM runs its full course from obvious onset to death from asphyxiation in about four years. Most corgis do not live to the point of actually having difficulty breathing, but either succumb to other age-related diseases or are euthanized when quality of life has diminished too far. Once a dog has survived the first year of IVDD, he will probably have a normal life span, but rarely myelomalacia or recurrent resistant UTIs will affect initial survival.
Bobbie Mayer is the author of “Corgis on Wheels: Understanding and Caring for the Special Needs of Corgis with Degenerative Myelopathy or Disk Disease”, which is available at http://www.corgiaid.org/cart/corgisonwheels or from Amazon.