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					STUDENT PAPER                                                               COMMUNICATION iTUDIANTE
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               Cervical stenotic myelopathy in a horse
                                                  Mary K. Mackie

        Abstract - A 13-year-old, Thoroughbred gelding presented with a 3-year history of progressive
        ataxia of all 4 limbs. Physical and neurological examinations indicated a compressive lesion
        affecting the cervical spinal cord. Radiographs confirmed a lesion, and a myelogram a narrowing of
        the spinal canal at cervical vertebrae (6-7). Necropsy confirmed cervical stenotic myelopathy.
        Resume - Myelopathie cervicale compressive chez un cheval. Un Thoroughbred hongre de 13 ans
        a ete presente pour une histoire d'ataxie aux 4 membres en progression depuis 3 ans. Les examens
        physique et neurologique ont montre une lesion compressive affectant la moelle epiniere cervicale.
        Des radiographies ont montre qu'il y avait une lesion, et un myelogramme a confirme le retrecissement
        du canal cervical au niveau des vertebres cervicales (6-7). La myelopathie cervicale compressive
        a 'te confirmee a la necropsie.
                                                                                     (Traduit par Docteur Andre Blouin)
        Can Vet J 2001;42:943-944



A 13-year-old, Thoroughbred gelding was presented                 impinging on the spinal cord, and led to a diagnosis of
      to the Western College of Veterinary Medicine               cervical stenotic myelopathy (CSM). The owner
(WCVM) with a 3-year history of progressive ataxia. The           requested euthanasia (Euthanyl, sodium pentobarbital;
horse had been losing weight for 6 mo despite having a            Bimeda-MTC, Cambridge, Ontario), and a myleogram
normal appetite.                                                  was performed postmortem. Diatrizoate meglumine
   The horse had a broad-based stance of both the fore-           66%-diatrizoate sodium 10% (Bracco Diagnostics
and hind limbs. The hooves of all 4 feet were squared off         Canada, Mississauga, Ontario), 60 mL, was injected
at the toe, because he dragged his feet at both the walk          into the cisterna magna subarachnoid space. A neutral
and the trot. He also displayed forelimb hypermetria.             neck position showed no major dislocation of any ver-
   Physical examination revealed a body condition score           tebral segments; however, a flexed lateral position
of 2 out of 5. Mild muscle atrophy was observed over the          revealed dorsal dislocation of the cranial aspect of C6.
sacrum and withers and in the gluteal region. Tempera-               At necropsy, the C6-C7 articular surface was rough
ture, pulse, and respiration rates were within normal ref-        and the spinal canal markedly stenotic over approxi-
erence ranges. A neurological examination revealed                mately 1 cm. The spinal cord at this site was dorsoven-
normal mentation and cranial nerve function. When                 trally flattened, yellow, and soft. The dorsal margins of
the horse was circled in either direction, his hind limbs         vertebral bodies C6 and C7 were raised and roughened
abducted and crossed over each other. The sway test was           and the osteophytes extended into the spinal canal.
positive bilaterally. When his head was held up, the              Light microscopic examination of multiple hematoxylin-
neurologic deficits were more obvious. These neurologic           and eosin-stained sections of spinal cord revealed mala-
findings are consistent with inadequate proprioception            cia with cavitation of the dorsal spinal tracts at C6-C7.
with upper motor neuron signs in the fore- and hind               There was complete absence of neurons in both the
limbs, secondary to a cervical lesion.                            dorsal and ventral horns of the grey matter. There was
   Cervical radiographs were completed and showed                 surprisingly little damage in the spinal cord caudal to the
that the intervertebral joint space between cervical ver-         area of compression; however, cranial to the compres-
tebrae 6 and 7 (C6-C7) had osteophytes on the cau-                sion, some areas of total loss of myelinated axons were
dodorsal aspect of C6 and the craniodorsal aspect of C7.          present in the dorsal (proprioceptive) tracts. The osteo-
These arthritic lesions protruded into the spinal canal,          phyte formation on the dorsal margins of the vertebral
                                                                  bodies extended into the dorsal part of the annulus
                                                                  fibrosus. The pathologic diagnoses were severe, subacute
Western College of Veterinary Medicine, University of             myelomalacia of the spinal cord and intervertebral joint
Saskatchewan, 52 Campus Drive, Saskatoon, Saskatchewan            degeneration at C6-C7.
S7N 5B4.
                                                                     Cervical stenotic myelopathy has multiple synonyms,
Dr. Mackie's current address is Calgary Humane Society,           including wobblers, cervical vertebral malformation/
1323-36th Avenue NE, Calgary, Alberta T2E 6T6.                    malarticulation, equine sensory ataxia (1), and equine
Mary Mackie will receive an animalhealthcare.ca fleece vest       incoordination (1,2). This condition occurs in all breeds
courtesy of the CVMA.                                             but is seen primarily in young male Thoroughbreds (3).
Can Vet J Volume 42, December 2001                                                                                        943
There are 2 types of CSM. A cervical vertebral instability                        Acknowledgments
(CVI) and a cervical static stenosis (CSS). Cervical          I thank Drs. Jonathan Naylor, Chris Clark, Gary Wobeser,
vertebral instability affects horses between 2 mo and         and Kimberly Tryon for their guidance.
2 y of age and is characterized by narrowing of the                                                                 cv.
sagittal diameter of the spinal canal (C3-C5) during
flexion of the neck (4). Cervical static stenosis most                                     References
commonly affects horses between 5 and 10 y of age and         1. Wagner PC, Grant BD, Reed SM. Cervical vertebral malformations.
involves vertebrae C5 to C7 (2). The case presented              Vet Clin North Am 1987;3:385-396.
                                                              2. Reed SM, Moore BR. Pathogenesis of cervical vertebral stenotic
here illustrates CSM in an older animal.                         myelopathy. Proc Annu Meet Am Assoc Equine Pract 1993:113-115.
   The differential diagnoses for CSM include equine pro-     3. Mayhew IG. Large Animal Neurology: A Handbook for Veterinary
tozoal myelitis, equine degenerative myelopathy, equine          Clinicians. Philadelphia: Lea & Febiger, 1989:246.
herpesvirus- 1, and trauma. Clinically, CSM has similar       4. Powers BE, Stashak TS, Nixon AJ, Yovich JV, Norrdin RW.
signs to equine degenerative myelopathy; however, the            Pathology of the vertebral column of horses with cervical static
                                                                 stenosis. Vet Pathol 1986;3:392-399.
age of onset in this horse (older) ruled out equine degen-    5. Radostits OM, Gay CC, Blood DC, Hinchcliff KW. Veterinary
erative myelopathy. Equine protozoal myelitis was                Medicine: A Textbook of the Diseases of Cattle, Sheep, Pigs, Goats
ruled out, because the neurological deficits were sym-           and Horses. Philadelphia: WB Saunders, 2000:1796.
metrical and the lesion was restricted to one location. The   6. Nixon AJ, Stashak TS, Ingram JT. Diagnosis of cervical vertebral
history of neurologic disease for several years did not          malformation in the horse. Proc Annu Meet Am Assoc Equine
                                                                 Pract 1982:253-266.
fit with equine herpesvirus-1. Trauma could not be            7. Robertson JT. Surgical treatment of cervical vertebral instability in
completely excluded but was unlikely given the thorough          horses. Proc Annu Meet Am Assoc Equine Pract 1993:117-119.
history.
   The narrowing of the cervical canal can be either
static or dynamic and most occur in a dorsoventral
plane (2). Some horses have altered bone growth of
the vertebral bodies, laminae, and articular processes.
Young horses can also have osteochondrosis and
osteoarthritis (2,6). Dynamic compression of the spinal
cord associated with subluxation at adjacent vertebrae
during flexion or extension of the neck also occurs (2).      The Canadian Biotechnology Advisory Committee (CBAC), an independent group of
Static narrowing is associated with a compressive lesion      experts representing a broad range of disciplines, has recently released an interm report
                                                              entitled Biotechnology and IntellectudTProperty: Patenting of Higher Life Forms
of the caudal cervical vertebrae and severe degenerative      and Related Issues. The report makes a number of draft recommendations conceming
osteoarthritis develops (2). Cervical static stenosis         the patentability of higher life forms and Canada's present patent system, and touches
is accompanied by hypertrophy of the ligamentum               on issues related to Canada's competitiveness and international obligations. The
                                                              report also asks Canadians to consider how best to address social and ethical concems
flavum (1).                                                   about patenting living organisms. The Committee hopes its recommendations will
   A tentative diagnosis of CSM can be established            encourage wide public discussion. To obtain a copy of this intenm report, or to let CBAC
based on history and clinical signs. Radiography or           know your views, please contact us. (A summary is available only on the Web site.)
myelography will confirm the diagnosis. Radiographic          Le Comite consultatif canadien de la biotechnologie (CCCB), un groupe d'experts
features, such as degenerative joint disease of articular     independants venus de toute une gamme de disciplines, vient de faire paraltre un rap-
facets, sclerosis of dorsal laminae, or soft tissue calci-    port provisoire intitule La biotechnologie et la propri6td intellectuelle: Le brevetage
                                                              des formes de vie superieures et les questions connexes. Le rapport ebauche un
fication dorsal to the intervertebral space and laminae of    certain nombre de recommandations concernant la brevetabilit6 des formes de vie
the caudal cervical vertebrae support the diagnosis of        supereures et le systeme canadien de brevets dans sa forme actuelle, et aborde aussi
CSM (6).                                                      des questions relatives a la comp6titivite et aux obligations intemationales du Canada.
                                                              Le rapport demande egalement aux Canadiens de refl6chir aux meilleurs moyens a
   Medical or surgical management of CSM in adult             prendre pour traiter les pr6occupations d'ordre social et ethique reliees au brevetage
horses is usually unrewarding (1,7). The necropsy find-       d'organismes vivants. Le CCCB espere que ses recommandations donneront lieu a un
ings reported for this case were consistent with those of     vaste ddbat public. Les personnes int6ress6es a se procurer un exemplaire ou un resume
                                                              de ce rapport provisoire, ou a faire part de leurs commentaires et points de vue,
Powers et al (4). The pathogenesis of CSM is related to       voudront bien s'adresser au CCCB de l'une ou l'autre des facons suivantes:
instability of vertebral articulation resulting in abnormal
biomechanical forces (4). The specific location of the           MaiVPoste: Canadian Biotechnology Advisory Committee
lesion at C6-C7 may be a result of increased mobility and                     Comit6 consultatif canadien de la biotechnologie
                                                                 5th Floor, Rm. 570E/5e etage, bureau 570E
a narrower canal in this region relative to the rest of the      240 Sparks St./240, rue Sparks
cervical vertebrae (4).                                          Ottawa, ON K1A 0H5
                                                                 Fax/T6l6copieur: (613) 946-2847
                                                                 Phone toll-free: 1-866-748-CBAC/T6lephone (sans frais): 1 866 748-CCCB
                                                                 Web site/Site Web: www.cbac-cccb.ca




944                                                                                            Can Vet J Volume 42, December 2001

				
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