Large Animal Neurology. Joe Mayhew

to horizontal and then swinging the head and neck to both sides through a horizontal arc of 60–90°. Facial symmetry, reflexes, movement, and especially muscle tone all can then be observed as well as the bulk and symmetry of the temporalis (Figure 2.3), masseter, and pterygoid muscles being compared. The symmetric bulk of all these muscles, plus other retrobulbar soft tissues, can be determined by the symmetry of depth of the supraorbital fossae. During facial reflex testing with blunt needle holders, sensation in the form of cerebral perception and resentment is evaluated from the nasal septum on each side. During this stage, any increased temperature and presence of sweat at the base of an ear will be evident. Nasal, oral, laryngeal, pharyngeal, and hyoid region inspection, and particularly palpation, is performed, and the external, palpable thoracolaryngeal responses are tested.

Figure 2.3 Many normal adult horses have slightly to moderately asymmetric temporalis musculature covering the temporal fossae (arrows). It appears the origins of the paired muscles on the temporal crest can arise asymmetrically even with there being no measurable asymmetry in muscle bulk. If there is asymmetry in such bulk of retrobulbar tissue (muscle), there will usually be asymmetry in eyelash angle, being more upright over the eyeball with less retrobulbar muscle bulk, as for the left eye here. Certainly, asymmetric dental disease most often will result in such findings.

       Body

      Neck and thoracic limbs

      Attention is immediately moved to the neck where bone and muscle symmetry is assessed by close palpation, and the local cutaneous coli and cervicofacial responses are seen and felt. A solid blunt instrument, such as 15–25 cm artery forceps or needle holders, is best for performing this and other cutaneous testing. On occasion, with a very frightened patient, the tip of a rigid index finger may have to suffice as being better tolerated. A firm thrust needs to be applied over sites at the level of and 10–15 cm dorsal to the articular processes of cervical vertebrae to consistently induce these cervical responses. The two‐pinch technique is used to test cervical dermatomes and to test limb autonomous zones for areas of hypalgesia if a reflex suppression or a final motor neuron lesion are suspected. Regional muscle atrophy, bony asymmetry, and areas of sweating are to be noted.

      Trunk and pelvic limbs

      Testing can continue caudally to transfer to the thorax testing the cutaneous trunci reflex over the mid‐third of the lateral thorax, again with forceful stimuli. There is a variable region over the point of the shoulder, about the C7–T3 dermatomal region, where neither responses are well obtained, and the cutaneous trunci reflex usually fades in the caudal thoracic region. Flexion, extension, and lateral bending of the thoracolumbosacral vertebral column is then conveniently tested with the instrument used to firmly stroke the lateral dorsum from the withers to the caudal gluteal region. Again, the two‐pinch technique is used to test lateral thoracic dermatomes and to test limb autonomous zones for areas of hypalgesia if there is any evidence whatsoever of a reflex or final motor neuron lesion. Regional loss of muscle bulk, bony asymmetry, and areas of sweating also should invoke detailed scrutiny.

      Rectum, bladder, anus, and tail

      Tail extension and flexion is evaluated during anal reflex and perineal sensory testing. A strong, blunt‐probe stimulus applied to the anal ring results in a brisk anal contraction and flexion (clamping) of the tail, whereas a light stimulus results in an anal reflex alone, and a soft, tactile stroking stimulus results in tail extension.

       Gait and posture

       The evaluation of posture and gait comprises the following minimal components:

       Observing the patient walking in a straight line viewed from the side as well as from behind and in front.

       Firmly but not abruptly pulling laterally on the tail with the patient standing still and while the patient is being walked forward.

       Assessing stride length and trajectory and placement of all four limbs both while walking freely and while the tail is pulled to each side in turn.

       Trotting the patient away from and back toward the examiner.

       Watching the patient being walked in circles and turning very tightly in circles in both directions.

       Taking the patient oneself and, by walking backward, leading the patient forward in a serpentine path to observe limb placement. In this maneuver, one leads in a manner such that the direction of each forefoot in turn is required to change direction during its swing phases.

       Leading the patient oneself to walk in circles and to turn tightly in circles in both directions.

       Continuing these maneuvers while pulling on the lead rope and the tail simultaneously, assessing limb placement and strength of resistance.

       Releasing the tail abruptly after stopping from turning tightly to observe for adoption of and standing with abnormal limb positions.

       Hopping the patient on at least the thoracic limbs (Figure 2.4).

      Manually placing the limbs in abnormal positions and placing them with the dorsum of the hoof resting on the ground are not useful in detecting neurologic motor or proprioceptive abnormalities in our hands. Likewise, the use of a sliding sack under one weight‐bearing foot in turn never alone appears to add information regarding the assessment of conscious proprioception.

A patient that is or can be placed in lateral recumbency can be tested for classical limb reflexes. In practical terms, these simply consist of the flexor reflexes in thoracic and pelvic limbs and the extensor or patellar reflex in the pelvic limbs; other described reflexes (responses) are very unrepeatable and unreliable in adult patients while trying to define an anatomic neurologic lesion site. A reflex is reported as present or hyperactive in a limb if such a normal or very strong response is detected in the recumbent patient while the limb is uppermost or is dependent. A clonic response is when there are multiple muscle contractions occurring in response to a single stimulus. A crossed extensor reflex occurs when there is limb extension into the untested limb in response to a graded, increasing stimulus to a distal limb. Hyperactive, clonic, and crossed extensor reflexes all reflect central motor pathway lesions with sparing of the final motor pathway.

Figure 2.4 Performing postural reactions such as hopping on one thoracic limb as shown can express underlying neurologic deficits. These include a slow onset of response on a limb with flexor weakness, a hypermetric response with spinocerebellar disease, and collapsing on a limb with extensor weakness. In larger patients where these testing procedures are difficult or impossible, such observations may depend on performing complex gait maneuvers such as turning tightly on a slope and walking the patient in a serpentine path and changing direction while one forelimb is protracting in its stride.

      All other limb reflex testing in adult patients really does not usefully contribute to a neuroanatomic diagnosis and results of such additional limb reflex testing should not be used to alter a neuroanatomic diagnosis achieved by the interpretation of results of the remainder of the examination. Finally, poor or absent reflexes can be found in a heavy patient very soon after the onset of recumbency,