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Atlantoaxial instability (AAI) is a condition characterized by excessive mobility due to trauma or congenital causes such as bone and ligamentous anomalies between the atlas (C1, 1st cervical spine) and axis (C2, 2nd cervical spine). It can cause varying degrees of neurological dysfunction due to cervical pain, spinal cord and root compression. While it can occur in dogs of all breeds and ages due to traumatic reasons, it can also occur due to congenital reasons such as anomalies of the dens and ligament structure. Congenital atlantoaxial instability is more common in small and toy breed dogs. The diagnosis of AAI can usually made by survey radiograph. Advanced imaging techniques allow the detection of cervical vertebral anomalies, the evaluation of existing spinal cord injury and syringomyelia. AAI can be treated conservatively or surgically. The case is 14 months old, 5 kg weight, a Miniature Schnauzer breed dog who was referred to the Surgery Clinic of Istanbul University – Cerrahpaşa Faculty of Veterinary Medicine with a history of unwillingness to play for 1-2 months, constantly licking his body and the air, making fly-catching movements, rubbing his paw on his face and neck pain.The patient had no history of trauma. At neurological examination, pain detected on palpation of the cranial cervical region and increased anterior and posterior leg tendon reflexes were detected. A diagnosis of atlantoaxial instability due to dens agenesis was made by evaluating the Magnetic Resonance Imaging (MRI), Computed Tomography and radiography. Since the clinical symptoms of the patient were not severe, conservative treatment was preferred. The patient was prescribed gabapentin at a dose of 10 mg/kg for neuropathic pain control. The dog has been under our follow-up for 4 months during this study and no abnormal findings were added during this period. The conclusion is that survey radiography alone is not sufficient in the diagnosis of atlantoaxial instability, CT has an important place in determining anomalies that may cause instability, and MRI has an important role in determining changes in the spinal cord structure.

Background: Spinal cord dysfunction/compression and ataxia are common in horses. Presumptive diagnosis is most commonly based on neurological examination and cervical radiography, but the interest into the diagnostic value of transcranial magnetic stimulation (TMS) with recording of magnetic motor evoked potentials has increased. The problem for the evaluation of diagnostic tests for spinal cord dysfunction is the absence of a gold standard in the living animal. Objectives: To compare diagnostic accuracy of TMS, cervical radiography, and neurological examination. Animals: One hundred seventy-four horses admitted at the clinic for neurological examination. Methods: Retrospective comparison of neurological examination, cervical radiography, and different TMS criteria, using Bayesian latent class modeling to account for the absence of a gold standard. Results: The Bayesian estimate of the prevalence (95% CI) of spinal cord dysfunction was 58.1 (48.3%-68.3%). Sensitivity and specificity of neurological examination were 97.6 (91.4%-99.9%) and 74.7 (61.0%-96.3%), for radiography they were 43.0 (32.3%-54.6%) and 77.3 (67.1%-86.1%), respectively. Transcranial magnetic stimulation reached a sensitivity and specificity of 87.5 (68.2%-99.2%) and 97.4 (90.4%-99.9%). For TMS, the highest accuracy was obtained using the minimum latency time for the pelvic limbs (Youden's index = 0.85). In all evaluated models, cervical radiography performed poorest. Clinical Relevance: Transcranial magnetic stimulation-magnetic motor evoked potential (TMS-MMEP) was the best test to diagnose spinal cord disease, the neurological examination was the second best, but the accuracy of cervical radiography was low. Selecting animals based on neurological examination (highest sensitivity) and confirming disease by TMS-MMEP (highest specificity) would currently be the optimal diagnostic strategy.

Background: Transcranial magnetic stimulation (TMS) and recording of magnetic motor evoked potentials (MMEP) can detect neurological dysfunction in horses but cutoff values based on confirmed spinal cord dysfunction are lacking. Objectives: To determine latency time cutoff for neurological dysfunction. Animals Five control horses and 17 horses with proprioceptive ataxia. Methods: Case-control study with receiver operating characteristic curve analysis, based on diagnostic imaging, TMS, and histopathological findings. Horses were included if all 3 examinations were performed. Results: Diagnostic imaging and histopathology did not show abnormalities in the control group but confirmed spinal cord compression in 14 of 17 ataxic horses. In the remaining 3 horses, histopathological lesions were mild to severe, but diagnostic imaging did not confirm spinal cord compression. In control horses, latency time values of thoracic and pelvic limbs were significantly lower than in ataxic horses (20 +/- 1 vs 34 +/- 16 milliseconds, P = .05; and 39 +/- 1 vs 78 +/- 26 milliseconds, P = .004). Optimal cutoff values to detect spinal cord dysfunction were 22 milliseconds (sensitivity [95% CI interval], 88% [73%-100%]; specificity, 100% [100%-100%]) in thoracic and 40 milliseconds (sensitivity, 94% [83%-100%]; specificity, 100% [100%-100%]) in pelvic limbs. To detect spinal cord dysfunction caused by compression, the optimal cutoff for thoracic limbs remained 22 milliseconds, while it increased to 43 milliseconds in pelvic limbs (sensitivity, 100% [100%-100%]; specificity, 100% [100%-100%] for thoracic and pelvic limbs). Conclusions and Clinical Importance: Magnetic motor evoked potential analysis using these cutoff values is a promising diagnostic tool for spinal cord dysfunction diagnosis in horses.

Cervical vertebral malformations can cause acute or progressive pain, paralysis, and potentially death. Herein we present a case report of dens agenesis; cervical vertebral malformations of C1, C2, C6, and C7; subluxation of C1 and C2 and C4 and C5; and associated degenerative myelopathy in a 5-month-old female Labrador Retriever puppy. We additionally review current knowledge regarding pathogenesis and treatment.