Horner syndrome as a physiological biomarker of disease in canine cervical myelopathy

BACKGROUND: Horner syndrome often occurs with cervical myelopathies and might provide insight into the underlying disease and prognosis. OBJECTIVES: To describe the clinical and imaging features of dogs with cervical myelopathy and concurrent Horner syndrome and to determine association of Horner syndrome with diseases or magnetic resonance images (MRI). ANIMALS: Ninety‐three client‐owned dogs with cervical myelopathy and concurrent Horner syndrome and 99 randomly selected client‐owned dogs with cervical myelopathy without Horner syndrome (control cases). METHODS: Retrospective study. Medical records were reviewed to identify Horner and control cases and clinical findings recorded. MRI were reviewed, and lesions characterized and recorded. Descriptive and comparative statistics were performed. RESULTS: Non‐compressive disease occurred more frequently in the Horner group compared with controls (58%; 95% CI: 48‐68 vs 9%; 95% CI: 5‐16; P < .0001). The most common diseases were fibrocartilaginous embolism in the Horner group (44/93; 47%) and intervertebral disc extrusion (76/99; 77%) amongst controls. On MRI, parenchymal hyperintensity was seen more commonly in the Horner group (95%; 95% CI: 88‐98) compared with controls (51%; 95% CI: 41‐60; P < .0001). In the Horner group, dogs that did not survive to discharge (N = 13) had more extensive MRI lesions relative to the adjacent vertebral length (200%; IQR 110%‐575%) compared with survivors (N = 80; 110%; IQR 40%‐250%; P = .02). Lateralization of Horner signs and MRI changes matched in 54% of cases. The overall survival rate was high in both Horner (80/93; 86%) and control (95/99; 96%) groups. CONCLUSIONS AND CLINICAL IMPORTANCE: Horner syndrome in cervical myelopathy is commonly associated with noncompressive intraparenchymal disease.