Mielomalácia hemorrágica ascendente secundária à protrusão de disco intervertebral em cão / Ascending Hemorrhagic Myelomalacia Secondary to Intervertebral Disc Protrusion in a Dog

ABSTRACT

Background: Myelomalacia is a multifocal syndrome that causes hemorrhagic infarction of the spinal cord that can occur as a sequel to acute spinal cord injury. It occurs as a consequence of acute spinal cord trauma, usually by extrusion of intervertebral disc in the thoracolumbar spine, affecting up to 10% of dogs with acute paralysis and deep pain loss in the pelvic limbs due to disc disease. This disease may be focal or diffuse; the diffuse form is typically associated with cranial and caudal migration of neurologic signs and is often fatal. The mechanical lesion to the spinal cord triggers secondary injury mediated by the existence of oxygen free radicals, alterations in the concentrations of neurotransmitters ions and amino acids, and it results in the reduction of the spinal cord blood flow, ischemia and progressive cranial and caudal necrosis to the focus of the initial injury. Case A 5-year-old Dachshund male intact dog weighting 8 kg was referred to the Veterinary Teaching Hospital of the Federal University of Rio Grande do Sul (HCV-UFRGS) with initial complaint of acute paralysis of the hind limbs for two days. On clinical examination there was paraplegia, absence of deep pain in the pelvic limbs, with decreased patellar, sciatic and tibial cranial reflexes. The anal sphincter was relaxed and the bladder was easily expressed. The panniculus reflex was intact up to the 10th thoracic vertebra (T10). The patient had exacerbated pain on palpation of the thoracic spine. The other physiological parameters were within normal limits. Based on clinical findings, ascending myelomalacia was the presumed diagnosis. Biochemical and haematological profiles were unremarkable. The myelographic examination did not reveal a site of spinal cord compression, as the column of contrast suffered no deviation or blockage in its path. Pain was medically managed. The following day, the animal had hypothermia, forelimbs paresis, dyspnea and abdominal breathing. The panniculus reflex had migrated cranially, to the height of the 6th thoracic vertebra (T6). The owner opted for euthanasia and the patient was referred to necropsy. At necropsy the L1-L2 intervertebral disc suffered disc protrusion and not extrusion. Along the spinal cord there was multifocal hemorrhage in the white and gray matter, with gliosis, malacia, fibrin deposition and axonal spheroids. In the lumbar spinal segments L1 and L2, there was neutrophilic infiltrate and calcification area in the meninges. Discussion: It is often cited in the literature that young dogs, especially the Dachshund breed, are prone to intervertebral disc disease, with acute paralysis and, in severe cases, myelomalacia ascending, as in this case. What is rare, though, is the occurrence of myelomalacia associated with disc protrusion only instead of disc extrusion. The multifocal character of the disease evidenced by changes and worsening of neurological signs in the course of the disease was reported in this case. The physical examination findings and its evolution are the same cited in the literature, such as atonic bladder, absence of patellar reflex, anal sphincter relaxation. Dyspnea is related to paralysis of the intercostal muscles and diaphragm and is irreversible and fatal. Early diagnosis of myelomalacia ascending hemorrhagic myelomalacia is crucial to prevent death from respiratory failure due to the progression of the disease. Effective treatment for preventing the progression of necrosis and hemorrhage resulting from spinal thoraco-lumbar disc disease, acute paraplegia and which leads to loss of deep pain has not been found yet.