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If the examination of the head, gait and posture, and neck and thoracic limbs reveals evidence of a nervous system lesion(s), then an attempt should be made to associate such lesions with any further signs found during examination of the trunk and hindlimbs. If there are only signs in the trunk and hindlimbs (Figure 2.16), then the lesion(s) must be between C₁ and S₂, but most probably between T₃ and S₂, or in the trunk and pelvic limb nerves or muscles. This part of the examination helps localize such lesions more precisely. However, the examiner must remember that with a subtle grade neurologic gait abnormality in the pelvic limbs, the lesion may be anywhere between the rostral brainstem and the mid‐sacral spinal cord.

Figure 2.16 This Holstein calf (A) suffered from vertebral trauma during an assisted delivery that resulted in paraplegia due to an epiphyseal separation at caudal L4 vertebra. With nursing care, the calf recovered quite well to be able to stand and walk but with a tendency to knuckle over on its fetlocks as shown. The residual gross lesion shown below (B), particularly the focal necrosis of dorsal gray and white matter at L_4‐5, explains the clinical syndrome that related mostly to bilateral deficits of the sciatic/peroneal nerve distribution with very poor flexor reflexes present in the pelvic limbs.

The trunk and hindlimbs must be observed and palpated for malformation and asymmetry (Figure 2.17). Lesions affecting thoracolumbar gray matter cause muscle atrophy, which is a helpful localizing finding. With asymmetric myelopathies, scoliosis of the thoracolumbar vertebral column often occurs, initially with the concave side opposite the lesion, but changing with subsequent fibrous contracture setting in. Once again, evidence of muscle atrophy, especially common over the gluteal region (Figure 2.18), should be taken as evidence of an underlying lameness until there is additional evidence that it is neurogenic.

Figure 2.17 Very occasionally, portions of muscles, whole muscles, or muscle groups are found to be absent and often there are no definitive neurologic signs present. Such was the case with this horse in which a large portion of the left medial thigh muscles, at least including the medial quadriceps group, was missing with no evidence of weakness or ataxia in either hind limb. Whether individual cases are congenital or acquired (from say S. neurona) is usually very difficult to determine when present for such a long time.

Figure 2.18 Proximal limb atrophy more often is due to disuse mostly because of orthopedic disease. However, selective middle gluteal muscle atrophy in the absence of lameness and the absence of atrophy of other proximal limb musculature as seen on the left side in this horse is likely to be due to final motor neuron disease such as that caused by S. neurona myelitis at L₆ as was the case here.

Sweating in the horse over the trunk and hindlimbs, excluding the neck and face, can be a helpful localizing sign. Ipsilateral sweating caudal to the lesion signals involvement of the descending sympathetic tracts in the spinal cord caudal to T₃. Lesions involving specific pre‐ or postganglionic peripheral sympathetic fibers that are second‐ and third‐order neurons cause saddles or patches of sweating at the level of the lesion.

Firm prodding of the skin over the trunk, particularly the mid‐lateral aspects of the thoracic wall, causes a contraction of the cutaneous trunci muscle, seen as a flicking of the skin over the trunk—the cutaneous trunci reflex. The sensory stimulus travels to the spinal cord in thoracolumbar dorsal spinal nerve roots at the level of the site of stimulation. Transmission is then cranial in the spinal cord to C₈–T₁, where the final motor neuron cell bodies of the lateral thoracic nerve are stimulated resulting in contraction of the cutaneous trunci muscle. Lesions anywhere along this pathway may cause suppression of the response, which is easiest to detect with an asymmetric lesion. In addition to this, an assessment of sensory perception from the trunk and hindlimbs (Figure 2.19) must be made. This appears as a cerebral, behavioral response to a two‐pinch stimulus described above, which includes the assessment of the autonomous zones for the pelvic limbs (Figure 2.15). Degrees of hypalgesia have been detected caudal to the sites of thoracolumbar spinal cord lesions, but only when they are severe.

The cutaneous trunci reflex should not be referred to as the panniculus reflex as panniculus refers to the subcuticular fat depots over the abdomen.

Stroking firmly with a blunt probe or pinching and pressing down firmly with the fingers over the thoracolumbar paravertebral muscles causes a normal animal to extend into a slightly lordotic stance and fix the thoracolumbar vertebral column. The patient also resists the ventral motion and usually does not flex the thoracic or pelvic limbs. Continuing this stimulus to the dorsal sacral region and caudally along the rump results in a degree of vertebral flexion and a kyphotic stance. A weak animal usually is not able to resist the pressure by fixing the vertebral column, and thus it overextends or overflexes the back and begins to buckle in the pelvic limbs. The onset of buckling can be viewed as the patella pops out of its “stayed” position during these maneuvers. With additional proprioceptive lesions, the patient can sometimes react to this test by sinking but with irregular swaying movements of the pelvic region on sinking and on recovery – truncal ataxia. Prominent back pain can result in poor responses and evidence of pain perception by, say, a grunt from the patient. With lumbosacral and sacroiliac orthopedic lesions, such responses may be more localized to be most evident with downward pressure on each tuber sacrale in turn.

Lordosis refers to extension, and kyphosis refers to flexion, of the vertebral column. There is no such thing as dorsiflexion.

Figure 2.19 This foal developed sciatic paralysis after being treated for Klebsiella sp. sepsis. This resulted from the development of severe empyema over the caudal hip, entrapping the sciatic nerve onto the pelvis. The knuckled fetlock while standing (A) and walking suggests peroneal branch involvement, and the analgesia from the caudal cannon region (B) is consistent with tibial nerve involvement.