Page 1081 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

1056 CHAPTER 10

VetBooks.ir 1 Palpate the depression just cranial to the cranial latero-oblique cervical radiography techniques
increase the sensitivity, specificity, positive predic-
edges of each tuber sacrale and caudal to the
caudal edge of the spine of L6. Plait and tie up
cervical vertebral lesions, compared with laterolat-
the tail. tive value and negative predictive value for detecting
2 After sterile preparation of the skin, 2–5 ml of local eral views, is debatable. However, in recent years, the
anaesthetic should be placed in the subcutis and a development of computed tomography (CT) equip-
skin incision made before insertion of the needle. ment with wide bore gantry openings (up to 80 cm)
3 An 18-gauge 15–18-cm (6–7-inch) spinal needle means that the entirety of the cervical vertebral
should be used in adults and an 18 or 20 gauge column and cranial aspect of the thoracic vertebral
9-cm (3.5-inch) spinal needle should be used column to T1–T2 can be imaged in the adult horse
in foals. under general anaesthesia. The superior quality of
4 A right-handed person should stand on the right images obtained means that, where available, this has
of the horse, resting their right wrist on the right superseded plain radiography of the cervical spine.
dorsal midline of the horse. The needle should be Given their smaller size, the entire vertebral column
inserted perpendicular to the dorsum of the horse of small ponies and foals can be imaged successfully
in both directions – it is useful to have an assistant via CT under general anaesthesia. Myelography is
standing back from the horse to advise on needle indicated in horses with neurological signs that can
direction. The depth of needle penetration to be attributed to a cervical spinal cord compressive
reach the LS space in the horse depends on their lesion on neurological examination.
size and obesity and is approximately 12.5 cm
(5 inches) in a 450 kg horse. Neuroelectrodiagnostic testing
5 When the dura–arachnoid is penetrated by Electromyography (EMG)
the needle, be prepared for a reaction in the EMG refers to the assessment of the electrical activ-
horse, such as tail flick, hindlimb flexion and ity of muscle. The distribution of abnormalities
muscle contraction. Sometimes the reaction is can help to confirm which spinal cord segment is
particularly violent and the horse handler should affected, or to give more precise differentiation of
be aware of this potential! nerve plexus or peripheral nerve disorders. However,
6 At this point, advance the needle slowly, and the findings are not specific or pathognomonic for
remove the stylet to check for CSF at 1 mm a particular aetiology or neuromuscular disorder.
intervals. The aim is to remove CSF from the EMG can be performed in the standing patient or
dorsal subarachnoid space, but sometimes the under general anaesthesia, and commonly utilised
CSF fails to flow from here, and the needle sedative drugs will not interfere with EMG readings.
reaches the ventral subarachnoid space on the Needle electrodes are placed in muscles, to detect
bony floor of the vertebral canal. At this location abnormalities when the needle is inserted or spon-
in the adult horse, this means the caudal sacral taneous abnormal activity. Abnormalities in inser-
segments will have been penetrated, and the tional activity include absent, increased, decreased
needle should be retracted slowly back up to or prolonged activity. Spontaneous abnormal activi-
reach the dorsal subarachnoid space. ties reported in neuromuscular disease include fibril-
7 As with the AO site, CSF should be collected in lation potentials, positive sharp waves and complex
serial small aliquots, not one large syringe, and repetitive discharges. It may take 2 weeks after the
the last one with the least blood contamination onset of neuromuscular disease for abnormalities to
should be submitted for laboratory analysis. appear in EMG recordings.

Radiography Electroencephalography (EEG)
Plain radiography of the skull and vertebral col- EEG is the graphic recording of rhythmic electri-
umn of the horse can be used to identify fractures, cal activity arising mainly from the cerebral cortex.
malformations and luxations. Whether oblique Normal patterns of activity have been reported in