Prevalence and Risk Factors for Presumptive Ascending/Descending Myelomalacia in Dogs after Thoracolumbar Intervertebral Disk Herniation

Background: Ascending/descending myelomalacia (ADMM) is a severe complication of thoracolumbar intervertebral disk herniation (TL-IVDH) in dogs. Hypothesis/Objectives: To investigate the prevalence and risk factors for ADMM in nonambulatory dogs with surgically treated TL-IVDH. Animals: Six-hundred and fifty-two client-owned dogs evaluated for TL-IVDH that underwent decompressive spinal surgery. Methods: Retrospective medical record review from February 2007 through December 2015. Results: Thirteen dogs developed ADMM, with an overall prevalence of 2.0%. The prevalence of ADMM was 0% in dogs with neurological signs graded 1 or 2 at admission or before magnetic resonance imaging (MRI) or surgical procedures, 0.6% in dogs with neurological signs graded 3, 2.7% in dogs with neurological signs graded 4, and 14.5% in dogs with neurological signs graded 5. Age (< 5.8 years), neurological status (grade 5), site of disk herniation (L5-L6), duration of clinical signs before becoming nonambulatory (< 24 hours), detection of intramedullary T2-weighted (T2W) hyperintensity, and a T2 length ratio > 4.57 were significant risk factors in the univariate analysis for development of ADMM. Conclusions and Clinical Importance: The factors identified in this study may be useful for the prediction of ADMM. Multicenter studies with a higher number of dogs with ADMM are required to confirm these data.