Large Animal Neurology. Joe Mayhew

Чтение книги онлайн.

Figure 3.8 Ultrasound‐guided collection of CSF from between C1 and C2 in a standing sedated horse (A and B). In C, the spinal cord (SC) and dura mater (green arrows) are imaged using a transversely oriented ultrasound transducer. A 3.5inch (8‐10 cm) 18 g styletted needle is introduced from below the transducer and advanced into the subarachnoid space, then the stylet is removed and CSF is aspirated into a syringe attached to extension tubing. The dashed orange line in C indicates a typical dorsolateral to ventromedial path of needle placement. The “Z” symbol at the top marks the dorsal aspect of the ultrasound image.

      Source: Images courtesy of Sally DeNotta, University of Florida, USA.

With most CNS malformations, the CSF analysis will be normal, although those anomalies that result in tethering of neural tissues such as complex vertebral deformations can result in progressive disease with ongoing traction injury to CNS neural tissues during growth, thus potentially resulting in CSF changes consistent with trauma. If a malformation of the calvaria or vertebral column damages underlying nervous tissue, the CSF may reflect compression with evidence of subtle hemorrhage.

      Infectious diseases can result in CSF pleocytosis and the elevation of protein content. The cell type present varies considerably, but generally neutrophils predominate with bacterial diseases and small mononuclear cells with viral diseases. Notable exceptions to this are high neutrophil numbers with Eastern equine encephalitis and high mononuclear cell numbers with listeriosis and equine neuroborreliosis. Fungal and protozoal diseases usually cause mixed cell responses. Protozoal, and particularly helminth parasite infestations, may produce an eosinophilic and neutrophilic response in the CSF, as well as hemorrhage. In contrast to bacterial meningitis where the neutrophils are degenerate and show toxic changes, with parasitic invasions and specific viral diseases the polymorphonuclear cells are nondegenerate and multilobulated due to their age. In most chronic inflammatory states and in diseases in which there is much CNS tissue necrosis, the CSF can contain many large mononuclear cells or macrophages.

      Although immune‐associated CNS disorders such as canine steroid‐responsive meningitis have not yet been reported in large animals, there would be an expected modest pleocytosis, usually mononuclear, and, extrapolating from canine practice, it may well be worth sampling CSF from both the cervical and lumbar regions to maximize the likelihood of identifying the major CSF cytologic response.⁵¹ This recommendation also likely holds true for many of the infectious spinal disorders.

      With traumatic injury to the CNS, there is often some hemorrhage into the CSF with resulting yellow discoloration that can persist for days after the insult. This xanthochromia remains after red cells have been centrifuged off. Neutrophils, not showing toxic changes, followed by macrophages, will usually appear in the CSF in response to hemorrhage.

      In most toxic, nutritional, and metabolic neurologic diseases, the results of routine CSF analyses are generally normal. However, for those diseases in which there can be considerable tissue destruction, such as lead poisoning, sodium salt/water intoxication and polioencephalomalacia in ruminants, and moldy corn‐associated leukoencephalomalacia in horses, there may be some protein leakage into, and a mononuclear cell response within, the CSF.

      Typically, there is leakage of protein and some xanthochromia without any significant pleocytosis in many vascular diseases. If the hemorrhage is large, then neutrophils and macrophages may also be seen.

Primary genetic (degenerative) diseases do not typically cause any changes in CSF constituents, and most frequently, the CSF analysis is normal. Early in the course of cell degeneration and especially in very young patients, some protein and even cellular response may be expected. Those resulting in the accumulation of products such as occurs in the storage diseases may result in macrophages containing waste material in the CNS and thence in CSF.

      Neoplasms can act like other space‐occupying lesions, such as abscesses, granulomas (such as cholesterinic granulomas in horses) and hematomas, and can increase intracranial pressure. The most frequent CSF change in patients with neoplasia is a slight elevation in protein content. Sometimes there is evidence of mild injury, xanthochromia, and a few macrophages. Rarely, there have been atypical lymphocytes detected in CSF from cattle with CNS lymphosarcoma. Atypical cells such as melanoblasts have been detected in CSF samples, but it is worth considering whether such cells may have been disrupted from meningeal sites during the course of CSF collection.

      Because of the lymphatic‐like drainage system of the CNS from perivascular and Virchow–Robin spaces ultimately to the subarachnoid space, any process that is contained within the parenchyma of the CNS may ultimately cause the leakage of pigments or protein, or the exfoliation of cells into the CSF.

Electrodiagnostic testing

Electroencephalography (EEG), needle electromyography (EMG) (Figure 3.2), quantitative EMG, and nerve stimulation and conduction testing contribute to a complete neurological evaluation. The techniques are used in large animals^52–63 and are the same as those used in small animal neurology.^64–66 An ambulatory EEG system has been described that allows telemetric recording from freely moving horses.⁶⁷ Considerable experience in using these ancillary aids is required to be able to interpret electrophysiologic studies in large animals because findings in normal animals are not well defined.^6068–70 This fact, and the expense of the equipment, makes these procedures rather out of reach for most large animal clinicians. However, visual evoked, brainstem auditory evoked, and other evoked potential testing (Figure 3.9) definitely have become more widely used in large animal neurology over the last decade or so, and references can be consulted for techniques and initial methods of interpretation.^71–84

Certainly, СКАЧАТЬ