The Cutaneous Trunci Muscle Reflex: A Predictor of Recovery in Dogs with Acute Thoracolumbar Myelopathies Caused by Intervertebral Disc Extrusions

Objective: To determine whether changes in the cutaneous trunci muscle (CTM) reflex are an early predictor of outcome in dogs with severe acute thoracolumbar intervertebral disc extrusion (IVDE). Study Design: Multicenter prospective cohort study. Animals: Dogs (n = 36) with acute IVDE causing paraplegia, loss of nociception in pelvic limbs and tail, and an abnormal CTM reflex postoperatively. Methods: The caudal border of the CTM reflex was established 24 hours after surgery and at discharge, and was reported as moving cranially, caudally, or staying static. Dogs were re-evaluated at 12-20 weeks and at 7-36 months postoperatively. Outcome was classified as improved or unimproved, successful or unsuccessful, and ascending myelomalacia or not, and compared with early movement of the CTM reflex by construction of contingency tables and performing a Fisher's exact test. Results: By discharge (mean, 4.7 days; SD = 2.10), CTM reflex progression was caudal in 19 dogs, static in 11, and cranial in 6. Five of 6 dogs with cranial movement developed ascending myelomalacia (P < .0001). Seventeen of 19 dogs with caudal movement showed an improvement by 12-20 weeks (P = .0046) and none developed ascending myelomalacia (P = .0013). Conclusions: Postoperative changes of the caudal border of the CTM reflex are an early indicator of outcome in dogs with severe acute IVDE. Cranial movement of the CTM reflex is significantly associated with the development of ascending myelomalacia. Caudal movement is significantly associated with improvement, but not associated with a long-term successful outcome.