Abstract
BackgroundWhen surgical treatment of cervical vertebral malformation is considered, precise localization of compression sites is essential, but remains challenging. Magnetic motor evoked potentials (mMEP) from paravertebral muscles are useful in localizing spinal cord lesions, but no information about cervical muscle mMEP in horses is available yet. Therefore, the aim of this study was to determine the possibility, normal values, inter- and intra-observer agreement and factors that have an effect on cervical mMEP in healthy horses.MethodsTranscranial magnetic stimulation was performed on 50 normal horses and 4 (2 left, 2 right) muscle responses were recorded at the middle of each cervical vertebra (C1-C7) and additionally just caudal to C7 to evaluate cervical nerves (Cn) Cn1 to Cn8. Latency time and amplitude of the recorded mMEP were defined by both an experienced and an unexperienced operator.ResultsLatency increased gradually from 14.2 ± 1.38 ms for Cn3 to 17.7 ± 1.36 ms for Cn8, was significantly influenced by cervical nerve (P < 0.01), gender (P = 0.02) and height (P = 0.03) and had a good intra-observer agreement. The smallest mean amplitude (4.35 ± 2.37 mV) was found at Cn2, the largest (5.99 ± 2.53 mV) at Cn3. Amplitude was only significantly influenced by cervical nerve (P < 0.01) and had a low intra-observer agreement. No significant effect of observer on latency (P = 0.88) or amplitude (P = 0.99) measurements was found.ConclusionmMEP of cervical muscles in normal horses are easy to collect and to evaluate with limited intra- and inter-observer variation concerning amplitude and should be investigated in future studies in ataxic horses to evaluate its clinical value.
Highlights
When surgical treatment of cervical vertebral malformation is considered, precise localization of compression sites is essential, but remains challenging
Factors univariably associated with latency were cervical nerve (P < 0.001), gender (P = 0.07), age (P = 0.05), height (P < 0.001), weight (P < 0.001) and sedation dose (P < 0.001)
50 8.8 4.1 2.6 19.8 2.7–19.8 n, number of magnetic motor evoked potentials recorded were tested, but only the interaction between cervical nerve and gender was significant (P < 0.01) (Fig. 3). This interaction signifies a different effect of the cervical nerve location on latency time for males and females
Summary
When surgical treatment of cervical vertebral malformation is considered, precise localization of compression sites is essential, but remains challenging. Many studies highlight the controversy, difficulties and limitations of cervical radiography, myeolography, computed tomography (CT), magnetic resonance imaging (MRI) and myeloscopy to diagnose spinal cord disease. Sensitivities (47–50%) and specificities (70–78%) of cervical radiographs and sagittal ratio calculations are too low for adequate diagnosis of spinal cord compression [5, 6] and variation between observers is high [7]. Most CT and MRI scanners can only image the cranial cervical spinal cord because of the limited diameter of the CT and MRI gantry. This is an important limitation since 37–54% of CVM lesions occur in the caudal (C5-C7) cervical vertebral column [6, 8]. The visual assessment of subarachnoid space narrowing may not be reliable in cases with mild to moderate stenosis [12]
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