Mielopatía degenerativa del Pastor Alemán

Degenerative Myelopathy of German Shepherd Dogs:

Introduction: Degenerative Myelopathy (DM) was first described as a specific degenerative neurologic disease in 1973. Since then, much has been done to understand the processes involved in the disease and into the treatment of DM. Hopefully, this will help you understand the problem and to explain further the steps that can be taken to help dogs afflicted with DM.
The age at onset is 5 to 14 years, which corresponds to the third to sixth decades of human life. Although a few cases have been reported in other large breeds of dogs, the disease appears with relative frequency only in the German Shepherd breed, suggesting that there is a genetic predisposition for German Shepherd dogs (GSD) in developing DM. The work presented here and by others on the nature of DM has been performed in the German Shepherd breed. Care must be taken in extrapolating this information to other breeds of dogs.
It is currently not known whether the exact condition exists in other breeds of dogs. Many dogs may experience a spinal cord disease (myelopathy) which is chronic and progressive (degenerative); but, unless they are caused by the same immune-related disease which characterizes DM of GSD, the treatments described herein may be ineffectual.
The breeds for which there is data to suggest that they also suffer from DM of GSD are the Belgium Shepherd, Old English Sheep Dog, Rhodesian Ridgeback, Weimaraner and, probably, Great Pyrenees.
Confirmation of the diagnosis is important in other breeds before assuming that they have DM of GSD.

Diagnosis of DM is made by a history of progressive spinal ataxia and weakness that may have a waxing and waning course or be steadily progressive.
This is supported by the neurologic findings of a diffuse thoracolumbar spinal cord dysfunction.
Clinical pathologic examinations are generally normal except for an elevated cerebral spinal fluid (CSF) protein in the lumbar cistern.
Electromyographic (EMG) examination reveals no lower motor unit disease, supporting the localization of the disease process in the white matter pathways of the spinal cord. Spinal cord evoked potentials recorded during the EMG do show changes which help determine the presence of spinal cord disease.
Radiographs of the spinal column including myelography are normal (other than old age changes) in uncomplicated DM. Unfortunately, myelography can be associated with worsening of clinical signs and carries some degree of risk for certain patients.

Dogs afflicted with DM have depressed lymphocyte blastogenesis to plant mitogens. The depression of their cell mediated immune responses correlates with the clinical stage and severity of the disease. Furthermore, this suppression has been shown to be due to the genesis of a circulating suppressor cell. Some dogs with DM exhibit antigen-binding cells specific to canine myelin basic protein. Immunoglobulins have been shown to be bound within lesions within the spinal cords of dogs with DM. These patients also show increased circulating immune-complexes in their sera. The antigens in these immune-complexes have been examined and appear to be markers of inflammation as they have been found to exist in patients who have other inflammatory diseases of the central nervous system. 2-Dimensional electrophoresis of CSF proteins indicates that the elevated proteins in the CSF of DM patients represent changes which are related to inflammation. While these changes are not specific for DM, the other conditions in which the inflammatory proteins have been found in CSF can be differentiated by clinical signs. The 2-dimensional electrophoresis of CSF proteins appears to be one of the most specific change seen in DM. Recently, we have found that CSF levels of the enzyme, acetylcholinesterase, are elevated in patients with DM. Again, this occurs in other forms of central nervous system inflammation in dogs.
However, when combined with the history, neurologic signs, CSF protein concentration and EMG, the elevated CSF acetylcholinesterase level helps confirm the diagnosis. This allows the inclusion of DM in the diagnosis, even if other problems are uncovered during the examination.
The gross pathologic examination of dogs with DM generally is not contributory toward the diagnosis. The striking features being the reduction of rear limb and caudal axial musculature.
The microscopic neural tissue lesions consist of widespread demyelination of the spinal cord, with the greatest concentration of lesions in the thoracolumbar spinal cord region. In severely involved areas, there is also a reduced number of axons, an increased number of astroglial cells and an increased density of small vascular elements. In the thoracic spinal cord, nearly all funiculi are vacuolated. Similar lesions are occasionally seen scattered throughout the white matter of the brains from some dogs, as well. Many patients have evidence of plasma cell infiltrates in the kidneys on throughout the gastrointestinal tract, providing a hint to the underlying immune disorder causing DM.

During the past two decades, at the University of Florida, have provided important new insights into the pathoetiology of DM. The release of antigens during the disease process could explain the immune deficits seen in DM and suggests that processing these immune-complexes by circulating macrophages leads to the development of the circulating suppressor cells that were previously noted. This provides a logical explanation for the presence of immune abnormalities in GSD with DM. Electrophoresis of immune-complexes demonstrates that the proteins present are inflammatory proteins which increase in inflammatory diseases of the dog nervous system. It is hoped that working with the antigens present in the immune-complexes will lead to a major breakthrough in our understanding of DM and that this also could lead to an early serodiagnostic test for the condition. However, the development of a serodiagnostic test will await the availability of antibodies specific to unique markers within the inflammatory proteins of DM dog immune-complexes. While the cause of the altered immune system is not known, what is increasingly clear is that DM is caused by an autoimmune disease attacking the nervous systems of patients, leading to progressive neural tissue damage.
In many respects, DM is similar to what has been discovered about the pathogenesis of Multiple Sclerosis in human beings. In fact, based upon new data concerning the pathology of MS, we can now say with some degree of certainty that DM is MS in dogs. We believe that, due to some triggering factor, immune-complexes circulate. These immune-complexes lead to endothelial cell damage in the vessels of the CNS. Subsequently, fibrin is deposited in the perivascular spaces. When this degrades (point of action of aminocaproic acid), inflammatory cells are stimulated to migrate into the lesions. The inflammatory cells release prostaglandins and cytokines (point of action of vitamin E and C) which leads to the activation of tissue enzymes and the formation of oxygen free-radicals (point of action of acetylcysteine) which, in turn, leads to tissue damage. Treatment of DM of GSD, which we recommend, is directed at these pathologic processes.

TRATAMIENTO DE LA MIELOPATIA DEGENERATIVA DEL PASTOR ALEMAN
FUENTE: Universidad de Florida (USA)