The early stages of Degenerative Myelopathy start with an almost imperceptible weakness in the hindquarters. DM is an insidious disease and it is all too easy to overlook, in it's earlier stages, unless you are specifically looking . Even then, DM is elusive and hard to detect.
(I always check the rear nails on a dog once a month for uneven wear, especially on the innermost nails of the rear feet, as this is an early tip-off to DM.)
In early and up to the mid-mid stage DM, occasionally you will hear the sound of the dogs nails scraping on the pavement during a walk. This scraping will not be constant; rather, will present periodically. The dog will begin to show some difficulty getting up. If the dog is standing, it may have difficulty balancing, but it can recover on its own. If you turn the dogs toes under in this stage, the dog may still be able to right its foot, although response time could be lengthened.
As the disease further progresses to late mid-stage, difficulty getting up increases. The nails begin to scrape more often on the pavement, until it becomes constant. As the disease progresses, the rear legs will cross under the dogs body as the dog, losing sensation in its hindquarters, will not know where it has actually placed its feet. Faulty perception of foot placement leads to tripping and stumbling.
When the dog is in a standing position, if you move the dog from side to side, using your hands, the dog will lose its balance and topple over. Often, you will notice exaggerated movements, such a high stepping when going up a curb. This is due to prioceptive functions being affected by DM.
The tail will rarely become active and wag. If the tail is longer, the dogs legs will easily become tangled in it. If the dogs foot is placed on the ground, toes down, the dog will not right its foot, or they may be a delayed response time. The reason for this delay is due to the fact that the dog cannot feel its foot; hence, the dog knuckles. A dog with feeling in its hind paws will have a quick/quicker response in placing its foot in the proper position. A dog with little or no feeling will have a slow or non-existent reflex action placing its foot in the proper, pad-down position.
As DM becomes more advanced, in early late-stage DM, uncontrolled jerkiness of the rear legs and tail signals that the nerve impulses are going haywire and short- circuiting. Kicking out with the rear legs, without reason, will be observed, along with the tail seeming to raise and lower, as if the dog is preparing to defecate.
Sometimes, if you pinch the pad of one foot, the other foot will respond. This is called Cross Extensor Response. Maintaining balance during defecation becomes almost impossible. When the dog squats, it will lose its balance and fall.
As the disease process reaches late stage, the dog will not be able to bear any weight, on its own, in the hindquarters. The affected dog will not be able to get up or, once lifted, will not be able to remain in a standing position, without some form of support for its hindquarters.