Diagnosis and Treatment of Degenerative Lumbosacral Stenosis

Chapter 238


Diagnosis and Treatment of Degenerative Lumbosacral Stenosis



Degenerative lumbosacral stenosis is a common radiculopathy in dogs and is noted most frequently in large working dogs. The most commonly affected breed is the German shepherd, but the disease also is encountered in other large breeds such as the Labrador retriever, golden retriever, and Doberman pinscher, and sometimes in smaller dogs. Males are more commonly affected than females, with reported ratios ranging from 1.3 : 1 to 5 : 1.


The lumbosacral region is bordered dorsally by the vertebral lamina, the articular facets, and the interarcuate ligament; ventrally by the dorsal longitudinal ligament, the annulus fibrosus, and the vertebral bodies of L7 and S1; and laterally by pedicles of the vertebral body. The intervertebral disk is attached to the cartilaginous end plates via strong collagen fibers called Sharpey’s fibers. The vascular system in the region is made up of a vertebral venous plexus and paired lumbar arteries. The spinal cord ends in the sixth lumbar region and terminates into the seventh lumbar, the sacral, and the caudal nerve roots. The L7 nerve roots pass over the intervertebral disk space and exit through the intervertebral foramen between the L7 and S1 vertebral bodies.


Stenosis involves the narrowing of the vertebral canal or intervertebral foramina in the lumbosacral region. Pathophysiologically the disease involves soft tissue and bony abnormalities that compress the nerve roots. Disk degeneration is evident in many cases. Causes of this degeneration may be related to lumbosacral instability, Hansen’s type II disk disease, or facet joint tropism (asymmetry of the left and right facet angles). Other causes of compression are diskospondylosis, osteophytosis, subluxation, hypertrophy of the interarcuate ligament, proliferation of the joint capsule, synovial cyst formation, and proliferation of the dorsal longitudinal ligament.



Diagnosis


Clinical signs of lumbosacral stenosis can be difficult to differentiate from those of other neurologic and orthopedic diseases. Signs include lumbosacral pain, hind limb paresis, urinary or fecal incontinence, pelvic limb lameness, muscle atrophy, dysesthesia, tail paresis, hyperesthesia or pruritus, and anal hyporeflexia. Owners often report that the dog has difficultly sitting, jumping, or climbing. To differentiate lumbosacral stenosis from other diseases such as canine hip dysplasia and degenerative myelopathy, diagnostic imaging becomes imperative.


The physical examination can help localize the cause to the lumbosacral region. Any changes in anal tone or tail function are an indicator of caudal nerve dysfunction. Decreased or absent hock flexion and a hyperreflexive patellar reflex can be indicators of sciatic dysfunction. Pain can be elicited directly by palpating over the lumbosacral region or by lifting the tail dorsally. Pelvic limb weakness can be evident on gait analysis and by observation of wearing of the nails on digits 3 and 4 of the hind limb paws. The findings of a comprehensive physical examination also can help guide the selection of optimal tests to arrive at the diagnosis and provide overall assessment of the dog.


Standard two-view radiographs are useful to assess bone changes in the lumbosacral region. Radiographs can reveal stenosis, diskospondylitis, osseous neoplasia, diskospondylosis, osteochondrosis, fracture, subluxation, and transitional vertebrae. Positional views, such as the extended and flexed views, can help determine whether movement of the lumbosacral region is normal and whether compression is present. In extension, the sacrum can displace ventrally and the vertebral canal is at its narrowest diameter. In flexion, the vertebral canal should be at its greatest diameter, but the diameter is decreased in dogs with lumbosacral stenosis.


Contrast studies can provide additional information beyond survey radiographs. Myelography is the least helpful of the contrast studies available. The dural sac termination site is variable in each dog. For myelography to provide diagnostic findings in cases of lumbosacral stenosis, the dural sac must extend into the sacrum. Diskography and epidurography provide better diagnostic information. Epidurography is used to evaluate neural compression (Figure 238-1). Diskographic abnormalities that confirm lumbosacral disease are intradiskal accumulation of the contrast agent, focal extravasation of contrast into the canal, and the presence of contrast within the disk. Transosseous and intravenous venography involve injection of a contrast agent into the vertebral venous sinus system to evaluate spinal cord compression indirectly.



Computed tomography (CT) provides cross-sectional images without the superimposition noted on radiographs. Dogs with lumbosacral disease have characteristic changes on CT images such as loss of epidural fat, dorsal bulging of the intervertebral disk, spondylosis, thecal sac displacement, narrowed foramen, narrowed central canal, thickened articular facets or joint capsule, articular process subluxation, and osteophytosis. Reformatting can create dorsal and sagittal images, and three-dimensional reconstruction also can make diagnosis of lumbosacral stenosis more visible.


Magnetic resonance imaging (MRI) provides the best soft tissue resolution, allows images to be acquired in multiple planes without degradation, and can detect disk degeneration earlier (Figure 238-2). Other advantages of MRI over CT are excellent visualization of the nerve roots, intervertebral disks, and ligaments and lack of exposure to ionizing radiation. MRI tends to be the most sensitive method for diagnosis of lumbosacral stenosis, but with excellent resolution also comes the potential for overdiagnosis. It is best to correlate imaging findings with the results of clinical assessment.


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Jul 18, 2016 | Posted by in PHARMACOLOGY, TOXICOLOGY & THERAPEUTICS | Comments Off on Diagnosis and Treatment of Degenerative Lumbosacral Stenosis
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