Large Animal Neurology. Joe Mayhew

(URLs logged March 2022)

Animal Genetics Inc.	Neogen Corporation
Biogenetic Services, Inc.	Quantum Genetix
Equine Neuromuscular Diagnostic Laboratory	UC Davis list of Cattle Genetic Testing Laboratories
Eurofins AgriGenomics	UC Davis Veterinary Genetics Laboratory
Genetic Testing at Gluck	VetGen
Genetic Visions‐ST	Zoetis Animal Genetics
Illumina Inc.

Cerebrospinal fluid analysis

The routine collection procedures for cerebrospinal fluid (CSF) sampling from large animals (Figure 3.2) have been described and simplified,^7–12 and techniques for the analysis of CSF samples have also been published.^12–19 Techniques for CSF collection from the horse are shown in Figures 3.3, 3.4, and 3.5, and those described for other large animals (Figure 3.6) can be extrapolated directly from the horse and from ruminants.^20–22 Ultrasound‐guided collection of CSF can also be considered,^23,24 and such ultrasound‐guided techniques for the collection of fluid from the atlantooccipital (Figure 3.7) and atlantoaxial spaces (Figure 3.8) in standing, adult horses can be useful in certain circumstances.^20–22,25 These are safe procedures using effective chemical restraint, although the possibility of inadvertent movement resulting in spinal cord penetration is always of concern. It is likely that worrisome signs of somnolence, stiff neck, and fever that resolves in a day or so following the cervical centesis occurs in a few cases. In neonatal foals, calves, camelids, and piglets, as well as sheep and goats, it is advantageous to use a 40–50 mm (1.5–2 inches), 20 ga disposable hypodermic needle with a plastic hub for all atlantooccipital CSF collections. These needles are exceedingly atraumatic, and in obtunded and in lightly sedated recumbent patients they cause minimal or no patient reaction. More importantly, CSF appears in the hub of the needle immediately after it enters the subarachnoid space. A sample can be obtained, and the needle withdrawn much more rapidly than if a styletted needle is used—very important in nonanesthetized patients. Indeed, during CSF collection from the cisterna magna of anesthetized dogs, it was shown that a stylet‐out technique was performed more rapidly and yielded a sample with less cellular debris than a stylet‐in technique using a standard CSF styletted needle.²⁶

Figure 3.2 Multiple tests were performed on this patient suspected of having a neuromuscular disorder. These included lumbosacral cerebrospinal fluid collection (1), needle electromyography (2), and muscle biopsies of type I and type II muscle‐fiber‐predominant muscles taken from sacrocaudalis dorsalis medialis and semitendinosus muscles at sites (indicated by 3 and 4), respectively.

Figure 3.3 Atlantooccipital cerebrospinal fluid collection from the recumbent horse. Spinal needle in position with stilette removed. Palpable landmarks are the cranial borders of the atlas (filled circles) and the external occipital protuberance (cross) on the dorsal midline.

      (Source: From Mayhew¹¹ with permission.

Figure 3.4 Lumbosacral cerebrospinal fluid collection from the standing horse. Spinal needle in position with stilette removed. Palpable landmarks are the caudal borders of each tuber coxae (filled circles), the caudal edge of the spine of L₆ (star), the cranial edge of the second sacral spine (filled triangle), and the cranial edge of each tuber sacrale (filled triangle).

      Source: From Mayhew¹¹ with permission.

Figure 3.5 Lumbosacral spinal fluid collection from the horse. Transverse dissection through lumbosacral articulations, cranial view. Spinal needle passes through the skin, thoracolumbar fascia adjacent to the interspinous ligaments, interarcuate ligament, dorsal dura mater and arachnoid, dorsal subarachnoid space, and conus medullaris. Needle point is in the ventral subarachnoid space. Inset shows the cranial view of pelvis, sacrum, and the area of dissection.

      Source: From Mayhew¹¹ with permission.

Figure 3.6 Performing CSF collection from the atlantooccipital (AO) (A) and lumbosacral (LS) (B) sites is very straightforward with appropriate restraint, sedation, and/or general anesthesia. In very young patients light sedation is adequate, and in obtunded patients simple restraint suffices to perform an AO collection. Collection of CSF from the LS site is easier with the patient standing as the landmarks are more easily palpable and symmetric.The landmarks are shown for the AO procedure in a calf (A) with the superficial site for skin penetration indicated by . This site is at the intersection of a line joining the cranial borders of the wings of the atlas indicated by linear marks, with the midline, indicated by the spot over the occipital protuberance, while the head is flexed 90° to the neck as shown. A 19–21g, 30–45 mm hypodermic needle with plastic hub is ideal for this procedure, allowing for CSF to appear in the hub instantly the subarachnoid space is penetrated. The basic site for an LS procedure (B) is where a line joining the caudal aspects of the wings of the ilia (yellow dotted line) crosses the midline, as indicated by . This coincides with a palpable depression between the paired tubers sacrale (TS) laterally and the dorsal spines of L6 and S2 on the midline—the spine of S1 normally being too short to palpate. An 8–20 cm, 18 or 20 g spinal needle with fitted stilette is used for all adult animals depending on their size.Penetration of the terminal spinal cord during an LS procedure is essentially inconsequential. Damage to the medulla oblongata, which occurs on pathologic inspection more often than is clinically suspected, can result in additional neurologic signs.

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