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Myelopathy and radiculopathy are also reported in association with spondylolisthesis. In the current case series, it is not known whether spondylolisthesis was primary, or developed secondarily to disc degeneration and joint instability. The high frequency of occurrence of degenerative changes in the intervertebral discs in the caudal cervical and cranial thoracic region (Bergmann et al. 2018) suggests that disc degeneration is primary. Neck stiffness and an abnormal posture to graze were the
most common clinical features. Difficulties in lowering the head to graze have been associated with congenital malformation of the occiput, atlas and axis (Dyson 2011) and with severe osteoarthritis of the articular process joints in the caudal neck region (Dyson 2011). One horse in the current series had concurrent osteoarthritis of the articular process joints of C7-T1 and both the ability to lower the head and forelimb lameness were markedly improved by intra-articular analgesia. To what extent intervertebral disc disease contributed to the clinical signs is difficult to determine. Lowering the neck to graze was a trigger for ‘neck locking’ in one horse (H5). It has previously been speculated that transient cervical nerve root compression may be a cause of ‘neck locking’ (Dyson 2011). This horse (H5) showed a pain response on the caudal
aspect of the left side of the neck only when the neck was ‘locked’. In a previous study of horses with postulated nerve root compression, one horse with unexplained forelimb lameness showed focal hyperaesthesia ipsilateral to the lame limb, and a horse with episodic root signature posture had ipsilateral focal allodynia only when standing in this posture (Dyson 2020). Focal hyperaesthesia was reported in 48% of 91 horses with cervical vertebral compressive myelopathy (Levine et al. 2010). Hyperaesthesia may be related to compression of a nerve root, dura or dorsal horn lesions. Two horses showed a propensity to stumble, which has
been documented previously in association with lameness postulated to relate to cervical nerve root impingement (Dyson 2020). Three horses showed forelimb lameness, in one of which deterioration in lameness was seen after distal limb nerve blocks, a feature that has previously been recognised in horses with possible cervical radiculopathy (Dyson 2020). Head tilt was observed in two of the four horses assessed ridden, a clinical feature also observed in some horses with forelimb lameness, possibly related to cervical radiculopathy (Dyson 2020). One of these horses also exhibited a tilt of the neck and head when the horse walked with the neck ‘locked’. Post-mortem examination of Horse 5 revealed how
radiography underestimated the degree of pathological abnormality of the affected vertebrae and rib articulations. The osseous changes of the vertebrae were similar to those described by Speltz et al. (2006). In the majority of horses, the owners were reluctant to
consider surgical fusion of the affected joints and for those with lesions caudal to C6–7 this would be logistically challenging. However, in one horse with lesions involving the C6–7 intervertebral symphysis surgical fusion was successful, allowing the horse to return to full athletic function as a dressage horse at Prix St Georges level. More horses require surgical treatment before the efficacy of this treatment could be assessed. In conclusion, cervical intervertebral disc disease is an
unusual cause of neck stiffness and an abnormal posture to graze and may be associated with forelimb lameness.
© 2019 EVJ Ltd
Authors’ declaration of interests No conflicts of interest have been declared.
Ethical animal research
The study was approved by the Clinical Ethical Review Committee of the Animal Health Trust (AHT 24 2018). Explicit owner consent for inclusion in this study was not sought, but all owners consented to the use of all case information and images for scientific publication.
Sources of funding There were no sources of funding.
Acknowledgements
Annamaria Nagy, Sigrid Grulke and Simona Cerri for contribution of Equidae to the study.
Authorship S. Dyson contributed to study design, study execution, data analysis and interpretation, and preparation of the manuscript. A. Salciccia and V. Busoni contributed to study design, study execution and data analysis and interpretation. All authors gave their final approval of the manuscript.
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