A 4-year-old, 7-kg, female spayed Maltese dog was referred to the University of Missouri Veterinary Medical Teaching Hospital for acute onset of ataxia and left thoracic limb paralysis. The dog had been normal earlier that day when allowed outside but became ataxic and recumbent shortly after re-entering the house. She did not appear to be painful at that time. The dog had no prior history of illness and was current on all vaccinations.The general physical examination was within normal limits except for otitis externa and the findings related to the nervous system. Upon neurologic examination, spontaneous vertical nystagmus was noted. All other cranial nerves were normal. Proprioception was slightly decreased in the left pelvic limb, and the left thoracic limb was paralyzed and lacked nociception. Muscle tone and spinal reflexes were normal except for the left thoracic limb, which was areflexic and hypotonic. The dog was laterally recumbent and unable to stand. She displayed no discomfort when the paralyzed limb was palpated or manipulated through a full range of motion. Likewise, no hyperesthesia was noted along the length of the vertebral column or during manipulation of the neck.On the basis of the neurologic findings, multifocal disease affecting the left lateral cervical intumescence and caudal brainstem was suspected. A CBC and biochemical profile were performed to eliminate metabolic disease. Clinicopathologic abnormalities were limited to increased alkaline phosphatase (430 U/L; normal, 20-157 U/L). Differential diagnoses at this point for the acute onset of tetraparesis included spinal vascular disease, traumatic injury, coagulopathy, inflammatory disease (granulomatous meningoencephalitis, breed-specific encephalitis), or infectious diseases (eg, rickettsial, protozoal, viral).The dog's condition had not changed the next day, and additional diagnostics were performed. Under general anesthesia, a cerebrospinal fluid (CSF) tap at the L5-L6 vertebral junction was performed before a myelographic study. However, hemorrhagic contamination complicated the interpretation of the CSF sample, and the decision was made

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