Approach
The diagnosis of the condition is based on clinical history, a thorough physical exam to rule out other possible etiologies of presenting symptoms, and consistent radiographic findings demonstrating narrowing of the spinal canal and/or neuroforamen. Other serious causes of low back and leg pain should be borne in mind when making the diagnosis.
History
Patients typically present with long-term symptoms of neurogenic claudication; these include pain and weakness in the thighs and calves and a sensation of numbness in the lower extremities when the patient walks. The symptoms tend to worsen as the patient continues to walk, and the patient is forced to lean forward while walking and eventually has to sit down to gain relief. This is because the spinal canal is narrowed with the lumbar extension that accompanies standing and walking, and the canal is enlarged with flexion that occurs when sitting. Patients usually have no trouble exercising on a stationary bicycle as they are able to remain sitting. Use of a shopping cart tends to provide significant relief. Spinal instability from an associated spondylolisthesis may result in sharp back pain from any body movement.
The physician should be aware of potential alternative diagnoses of low back and leg pain. A history of prostate, breast, lung, kidney, thyroid, or other malignancy and/or unexplained weight loss, combined with back pain and neurologic symptoms present for a relatively short duration (days to a few months), would alert the clinician to the possibility of spinal metastases. History of exposure to tuberculosis or HIV, or of intravenous drug use, may suggest these as pathologies responsible for spinal infection as a differential diagnosis. Neurogenic claudication can also be confused with vascular claudication. A thorough vascular exam should be performed on patients with spinal stenosis, and referral for vascular evaluation should be made for patients without palpable pulses or other signs of vascular insufficiency.
Exam
There are no consistent positive findings on physical exam to support the diagnosis, but patients often adopt a stooped posture while walking. Signs of vascular insufficiency and hip osteoarthritis suggest an alternative diagnosis. Major neurologic deficits are surprisingly uncommon, even with severe stenosis. Acute neurologic deficits should alert the physician to alternative diagnoses such as disk herniation or malignancy. Muscle weakness or atrophy, if present, may result from coexisting nerve root compression from an intervertebral disk herniation or severe lateral recess stenosis. Painless weakness is a rare presentation of spinal stenosis, and other neurologic conditions should be excluded. A wide-based gait, pathological reflexes, and spasticity may suggest a myelopathy or other systemic neurologic illness. Signs of radiculopathy such as specific muscle weakness, dermatomal numbness, or decreased reflexes may also be seen.
Magnetic resonance imaging (MRI)
MRI without intravenous contrast is the preferred initial modality in diagnosing spinal stenosis. It provides excellent anatomic detail of the cauda equina and nerve roots in the neural foramina, in both the axial and sagittal planes. MRI also delineates the levels of neural compression, the severity of compression, and any anatomic variations such as a tethered spinal cord and conjoined nerve roots, or arachnoiditis, which are all conditions that may substantially alter management. In addition, MRI can exclude other serious differential diagnoses such as tumors (including metastatic disease) and infection. Patients who have undergone prior lumbar spinal surgery should undergo MRI with and without intravenous contrast, as contrast may aid in distinguishing between scar tissue, recurrent disk herniation, and thickened ligament. MRI is not indicated for low back pain in the absence of radicular or claudication symptoms.[21]
Radiographs
Plain x-rays should be ordered in the initial workup in all patients for whom surgical treatment is to be considered. Radiographs do not directly image the dura and spinal nerves, and therefore provide only supportive information to that provided by MRI and computed tomography (CT). When vertebral slippage (spondylolisthesis) or spondylolysis is present, flexion and extension views may be helpful, as the presence and degree of instability may alter the surgical management.
CT with or without myelography
For patients unable to undergo MRI because of severe claustrophobia or non-MRI-compatible implanted medical devices such as cardiac pacemakers, myelography with CT scanning is the definitive imaging test. CT scanning provides superior anatomical detail of bone compared with MRI, and is highly sensitive in detecting bony abnormalities such as spondylolysis; and with myelography provides excellent visualization of the cauda equina and lateral recesses. Myelography, however, is an invasive procedure insofar as a lumbar puncture is necessary to introduce contrast media; therefore, a conventional lumbar CT scan is typically performed initially and the myelogram is reserved for patients considered for surgery.
Electrodiagnosis
Resting electromyogram (EMG) is generally not helpful, although some have suggested the use of dynamic electrophysiological studies to detect changes related to walking. For these studies, electrophysiological parameters are studied before and after patients perform an exercise treadmill test. One investigation suggested that patients with stenosis demonstrated a greater prolongation in latency on nerve conduction studies than those without stenosis, although the differences were not large enough to be clinically useful.[22] Electromyographic paraspinal mapping is a sensitive method and may reflect the physiology of nerve roots better than limb EMG. It may be useful for presurgical evaluation with more equivocal clinical and radiographic findings. Routine electrophysiological tests (EMG, nerve conduction study, F-wave response, Hoffmann-reflex, somatosensory evoked potentials, motor evoked potentials) have no diagnostic value for lumbar spinal stenosis.[23]
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