Cervical Spinal Cord

Animals with incomplete section of the cervical region of the spinal cord display hemiparesis or tetraparesis. The clinical signs include knuckling, stumbling, failure to lift the inside feet when turned in a tight circle, circumduction of the outside pelvic limb during circling, interference, hypometria or hypermetria, abnormal postural placement responses, crossing over midline when turned, and excessive truncal sway.

Lesions from C6 to T2 spinal segments (i.e., brachial intu­mescence) result in proprioceptive deficits in all four limbs and tetraparesis or tetraplegia (recumbency). There is flaccidity and hyporeflexia of the thoracic limbs and hypertonia and hyper­reflexia of the pelvic limbs. Unilateral lesions result in ipsilateral signs. Lesions of C6 to T2 segments involving white but not gray matter do not produce thoracic limb hypotonia. Perception of painful stimuli over all four limbs may be reduced. Flexor reflexes in the thoracic limbs may be depressed but are normal in the pelvic limbs. The righting responses of the head and neck are normal, but the animal may have difficulty rolling onto its sternum from a laterally recumbent position.

Lesions of the thoracolumbar region (T3 to L3 inclusive) cause paraparesis and ataxia in the pelvic limbs but usually do not affect the thoracic limbs. There may be knuckling, stum­bling, abduction, adduction, interference, excessive truncal sway, circumduction of the outside limb, and failure to lift the inside foot when pivoted in a tight turn. With complete lesions, the animal becomes recumbent but intermittently assumes a dog-sitting position, with the thoracic limbs extended and weight bearing and the pelvic limbs flexed. Muscle tone and spinal reflexes are exaggerated in the pelvic limbs. The urinary bladder is distended and, because of poor coordination of bladder filling with detrusor and sphincter tone (dyssynergia), residual volume is large. The tone of the urethral sphincter is normal. Rarely, animals with severe spinal cord lesions between T2 and L2 display transient hypertonia of the thoracic limbs (Schiff-Sherrington syndrome).⁵⁵ This condition is caused by interference with inhibitory fibers ascending from the lumbar segments in the dorsal funiculi to the lower motor neurons of the thoracic limbs.⁵⁵ These fibers synapse on the lower motor neurons of the brachial intumescence. Hypertonia from this deficit may be differentiated from cervical cord lesions by the lack of conscious proprioceptive deficits in the thoracic limbs of animals with thoracolumbar lesions.

The lumbosacral region (L3 to S2) of the spinal cord contains lower motor neuron efferents to and general proprioceptive afferents from the pelvic limbs. Lesions in this area result in paraparesis or paraplegia. Affected animals are ataxic and have conscious proprioceptive deficits of the pelvic limbs. Patients with complete spinal cord lesions of L3 to S2 exhibit flaccid paraplegia, which is accompanied by hyporeflexia or areflexia of the pelvic limbs. With prolonged denervation, there is neurogenic atrophy of the pelvic limb musculature.

Lesions located between L3 and L6 spinal cord segments result in urinary bladder distention and maintenance of a large residual volume. The sphincter tone is intact, but urine is not voided unless the intravesicular pressure exceeds that of the sphincter. These animals usually have contact dermatitis of the perineum and preputial area because of urine scalding. Lesions located around the S1 and S2 segments result in bladder distention and flaccidity. Urine may drip continuously from the urethral orifice, and perineal or preputial scalding can be present. The rate of flow may be increased by manually pressing on the bladder during a rectal examination.

Lesions of the sacrococcygeal (S3 to Cd5) spinal cord segments or cauda equina produce flaccidity and muscular atrophy of the tail and anus and, in males, penile paralysis (paraphimosis). Lesions in this area also result in desensitization of the tail, penis, vulva, rectum, anus, and perineum. The urethral sphincter is dilated, and urine constantly drips from the urethral orifice. The animal does not evacuate the bladder and is unable to defecate, resulting in a large dilated urinary bladder and distention of the rectum with feces (obstipation).

If the entire neurologic lesion is located caudal to S2, ataxia or limb weakness is not seen. The combination of flaccidity of the tail and anus and the constant urine leakage produces contact dermatitis of the perineum and pelvic limbs. Perineal scalding is characteristic of lesions of the cauda equina. Specific diseases of the spinal cord, peripheral nerves, and motor end plate are listed in Table 8.12.