Clinical Neurology, An Issue of Veterinary Clinics: Equine Practice , livre ebook

Clinical Neurology , Vol. 27, No. 3, December 2011
ISSN: 0749-0739
doi: 10.1016/S0749-0739(11)00070-8

Contributors
Veterinary Clinics of North America: Equine Practice
Clinical Neurology
GUEST EDITOR: Thomas J. Divers, DVM
College of Veterinary Medicine, Cornell University, Ithaca, NY 14853
Amy L. Johnson DVM
Department of Clinical Studies, University of Pennsylvania School of Veterinary Medicine, 382 West Street Road, Kennett Square, PA 19348
ISSN  0749-0739
Volume 27 • Number 3 • December 2011

Clinical Neurology , Vol. 27, No. 3, December 2011
ISSN: 0749-0739
doi: 10.1016/S0749-0739(11)00071-X

Contents
Cover
Contributors
Forthcoming/Recent Issues
Clinical Neurology
Differentiation of Ataxic and Orthopedic Gait Abnormalities in the Horse
Lesions of the Equine Neck Resulting in Lameness or Poor Performance
Advanced Imaging of the Nervous System in the Horse
Neuro-ophthalmology in Horses
Miscellaneous Neurologic or Neuromuscular Disorders in Horses
Toxins and Adverse Drug Reactions Affecting the Equine Nervous System
Evaluation and Management of the Recumbent Adult Horse
Guttural Pouch Diseases Causing Neurologic Dysfunction in the Horse
Update on Infectious Diseases Affecting the Equine Nervous System
Metabolic Causes of Encephalopathy in Horses
Index
Clinical Neurology , Vol. 27, No. 3, December 2011
ISSN: 0749-0739
doi: 10.1016/S0749-0739(11)00072-1

Forthcoming/Recent Issues
Clinical Neurology , Vol. 27, No. 3, December 2011
ISSN: 0749-0739
doi: 10.1016/j.cveq.2011.08.011

Preface
Clinical Neurology

Thomas J. Divers, DVM tjd8@cornell.edu
Department of Clinical Sciences, College of Veterinary Medicine, Cornell University, Ithaca, NY 14853, USA

Amy L. Johnson, DVM amyjohn@vet.upenn.edu ,
Department of Clinical Studies - New Bolton Center, University of Pennsylvania School of Veterinary Medicine, 382 West Street Road, Kennett Square, PA 19348, USA

Thomas J. Divers, DVM Guest Editor
Amy L. Johnson, DVM Guest Editor
Equine neurology is one of the most fascinating and challenging aspects of equine practice. Neurologic disorders can affect any age horse and can result from many different infectious and noninfectious causes. The horse's nervous system extends throughout the body and, when diseased, may cause a variety of clinical signs depending on which segments of the nervous system are involved. Even after a thorough neurologic examination, we may not be able to arrive at a specific diagnosis since clinical signs are sometimes subtle and often nonspecific for any one particular neurologic disease. There may be difficulty in determining if a gait abnormality is due to a neurologic or a musculoskeletal disease in some cases, and many neuroimaging techniques are not readily available to the practitioner. Progress is being made though, as recent advances in imaging, electromyelography, specific disease testing, and programmed gait analysis are improving our ability to diagnose neurologic dysfunction in the horse and determine specific causes. Additionally, we now better understand how important normal neck movement is to the horse's gait and that musculoskeletal diseases of the neck may cause gait abnormalities that can often be confused with spinal cord disease.
Two of the most controversial and written-about disorders in the horse, equine protozoal myeloencephalitis and equine herpesvirus 1, are both infectious neurologic disorders with frequent new discoveries being made from ongoing research. Rabies, another infectious disease of the nervous system, will always be of special concern to the equine practitioner due to its zoonotic potential. Encephalopathic diseases and blindness caused by neurologic disorders in the horse often have acute and dramatic clinical signs, sometimes making it difficult to safely approach and treat those horses. Bizarre behavior and other neurologic signs due to cerebral or neuromuscular dysfunction may also occur as a result of adverse drug reactions or intoxication. Another very interesting and species-unique aspect of equine neurology is that peripheral neuropathies may occur secondary to guttural pouch disorders and temporohyoid arthropathy.
It is not possible in this issue to cover all diseases of the equine nervous system. Instead, our goal here is to provide information on various aspects of the equine nervous system that may not be commonly covered in-depth in textbooks or conferences and to provide updates on other frequently discussed disorders. We would like to thank all the wonderful authors who have taken time out of their busy schedules to write articles and share their knowledge.
We hope you will find these articles useful in your practice and to be of help in diagnosing and treating neurologic conditions in the horse. We would like to thank all those veterinarians interested in neurology who have previously contributed information on the equine nervous system in textbooks, scientific publications, and conference presentations. We are hesitant to name those many individuals who have contributed so much to our understanding of neurology for fear of leaving someone out and you already know from your readings of their articles and textbooks and attending conferences who these individuals are. We would, though, like to recognize Dr Alexander de Lahunta and Dr Jill Beech, who helped pioneer the field of equine neurology and had a big influence on both of our careers. Thank you “Dr D” and Dr Beech and to all fellow equine practitioners; happy reading about the following selected aspects of equine neurology.
Clinical Neurology , Vol. 27, No. 3, December 2011
ISSN: 0749-0739
doi: 10.1016/j.cveq.2011.08.007

Differentiation of Ataxic and Orthopedic Gait Abnormalities in the Horse

Theresia F. Licka, Dr med vet, Mag med vet, MRCVS a , b theresia.licka@vetmeduni.ac.at ,
a Department for Small Animals and Horses, Orthopedics in Ungulates, Equine Surgery, Veterinaerplatz 1, Veterinary University Vienna, Vienna A-1210, Austria
b Royal (Dick) School of Veterinary Studies, University of Edinburgh, Scotland, UK

Keywords
• Equine lameness • Equine ataxia • Neurology • Orthopedics • Wobbler
Movement and, to some degree, posture at stance or even in recumbency depends on the functionality, interaction, and integration of the passive and active musculoskeletal structures, with pattern generation, motor innervation, and proprioception as the relevant neurologic aspects. Any abnormality within this arrangement will lead to a gait or movement deficit, and complex interactions can be present, such as the reduction of proprioceptive input due to damage of sensory nerves associated with orthopedic disease. A possible explanation for the slapping hoof placement in horses with laminitis, which was described to be similar to the gait of some “wobblers,” 1 could therefore be the damage to the sensory nerve fibers associated with pedal bone displacement and laminar disruption. An additional complicating factor is the increased incidence of orthopedic trauma and/or disease in neurologically impaired horses, as they are more prone to falling, stumbling, slipping, etc, than neurologically intact horses. In such cases, a degree of orthopedic pain may accompany ataxia.

Stance
While the postural sway in healthy young horses was described to be very consistent, 2 this has not yet been measured in ataxic or lame horses, and the following information on horses is therefore based on clinical experience. At stance, most orthopedic, pain-related disorders will produce a uniform, consistent posture, which reduces discomfort during standing . If more than one limb is affected, weight-shifting and alternating resting of limbs may occur. If the horse is turned or backed, a similar body position will be reached. This is different from ataxia, where the center of gravity of the body is not supported consistently with the same limb arrangement, but with a larger variety of limb positions. After any intervention, such as a tail-pull or a gentle rocking of the pelvis, the resulting limb positions in relation to the trunk and limb orientations in relation to the body axis can be different from the original situation.
In lactating sows, the high correlation between abnormal posture and foot lesions has been documented, even though the type of abnormal posture was rather vaguely defined as “weight persistently unequally distributed, no weight borne on the affected limb or limb elevated from the ground. 3 ” In cattle, the postural abnormality of arching the back was described as a rapid screening method for lameness. 4 In goats with transmissible spongiform encephalopathies, postural deficits described as a hunched appearance, with crouching or standing with the legs wide-based, were not found to be significantly more frequent than in control animals, 5 also indicating that these are transient phenomena in neurologic impairment. Also, such postural anomalies may have a low sensitivity for detection of encephalopathies.
Wide-based stance, especially of the hindlimbs, is commonly described in ataxic horses. This wide-based stance will increase the stability of stance, as the area of support under the center of gravity is increased, and it is probably the result of some residual sensation or awareness of being at risk of falling over. Only rarely will an orthopedic disorder produce a similar stance, if loading of the lateral aspects of the limbs is painful.

Practical