Parapareis (weakness in the rear limbs) and paraplegia (paralysis of the rear limbs) unaccompanied by signs of additional CNS disturbance suggests that the disease is located caudal to T2.
If the rear limb reflexes are intact, the lesion is between T2 and L3. If the rear leg reflexes are diminished to absent, the lesion is between L4 and S2.
This can be refined further in that lesions between L4 and L5 result in loss of femoral nerve function, manifested as a decrease in the patellar tendon reflex and inability to support weight in the rear legs.
Lesions between L6 and S2 result in sciatic nerve dysfunction, reducing rear leg withdrawal, cranial tibialis muscle, gastrocnemius muscle and sciatic nerve reflexes.

The differential diagnosis of paraparesis and paraplegia include a number of congenital diseases, including vertebral malformations, various spinal cord malformations, multiple cartilaginous exostoses, lysosomal storage diseases, and breed-specific disorders. Other disorders are similar to those which affect the cervical spinal cord including meningomyelitis (from various causes), degenerative disc disease, spinal cord trauma, fibrocartilaginous infarction, and neoplasia. In some breeds, the differential also includes degenerative myelopathy.

Diagnostic Approach:
The neurologic assessment of patients with rear leg problems helps to confirm that the disease is neurologic in nature and its location. Weakness can indicate neurologic disease, muscle disease or systemic illness. On the other hand, reproducible deficits in proprioception usually is indicative of neurologic disease, whether knuckling, stumbling or falling or conscious proprioceptive deficits or dysmetria of unconscious proprioceptive dysfunction. When deciding whether a rear leg lameness is secondary to orthopedic or neurologic disease, examination of proprioceptive function can help make the differentiation.
Unlike cervical disease, there are several neurologic tests which can assist in lesion localization with TL disease. If the lesion is between T2 and L3, Schiff-Sherrington syndrome may be seen. Also, between T2 and L4 is the panniculus response, where superficial stimulation of the skin over the back results in stimulation of intraspinal pain pathways with the resultant contraction of the latisimus dorsi muscle. Due to the overlap of sensory dermatomes, the panniculus response will be absent 1-2 segments caudal to the lesion. Hyperpathia on deep palpation will be present at the cranial edge of the lesion and hyperesthesia will be evident on pin prick of the skin at the cranial and caudal edges of the lesion. By locating hyperpathia and hyperesthesia and demonstrating the loss of the panniculus response 1-2 segments caudally, the lesion is found.
The ancillary diagnostic tests for TL spinal disease are identical to those for cervical disease with the exception that lumbar CSF should be obtained in most instances. Since the flow of CSF is from cranial to caudal, lumbar CSF more accurately represents changes within the TL spinal column. This is usually obtained by carefully passing a needle into the subarachnoid space between L5-L6 or L4-L5.

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