Catherine A. Loughin,     Plainview, New York

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.