MR techniques are constantly advancing. For example, there are now MR scanners that allow subjects to stand during the examination. One of the reasons that an inexact correlation exists between MR findings and clinical symptoms may be the supine position of patients in the MR tube, because the lying position minimizes canal narrowing. Recreating the most symptomatic position for the MR evaluation may maximize the anatomic abnormalities that cause compression. I predict that studies in the upright position will become the preferred diagnostic method for spinal stenosis as the technology improves and the scanners are readily available.
Computed tomography (CT) is an excellent technique to identify the osseous structures crowding the spinal canal. Myelographic dye enhances the resolution. I rarely order CT myelograms because I see this type of evaluation as a pre-operative test and expect the spinal surgeon to order one once a decision involving decompression surgery has been made.
Electrodiagnostic Tests
Electromyography (EMG) and nerve conduction tests (NCTs) are not routinely used to evaluate spinal stenosis. EMG and NCTs are abnormal in a proportion of spinal stenosis patients with persistent radicular symptoms, and the most common finding is bilateral multilevel radiculopathy. EMG cannot consistently predict the specific level of nerve compression associated with leg pain. EMG’s greater utility lies in determining the presence or absence of peripheral neuropathy and peripheral nerve entrapment syndromes that may be present simultaneously in an elderly population. It is in this circumstance that I utilize these tests. Somatosensory potentials may have sensitivity to identify levels of nerve root compression, however, they may be affected by processes that affect the peripheral nerves, nerve roots, dorsal columns of the spinal cord, and brain. Abnormalities are not specific for spinal canal lesions.
Differential Diagnosis
A recent systematic review examined the accuracy of diagnostic tests for lumbar spinal stenosis.10 The review of 41 studies concluded that no clinical, radiographic, or interventional injection method was the “gold standard” for the diagnosis of spinal stenosis.
With few evidence-based studies to identify definitive tests for its diagnosis, lumbar spinal stenosis remains a clinical diagnosis characterized by specific historical and physical findings and confirmed, but not diagnosed, by radiographic techniques documenting compression of neural elements.
Leg pain is caused by a number of ailments in the elderly. Vascular claudication is manifested by leg pain associated with physical activity that radiates from the foot or calf, proximally. Vascular insufficiency causing lower leg pain associated with riding a bicycle is a helpful finding in differentiating between the two forms of claudication. Hip arthritis will cause pain with walking but rarely below the knee. Peripheral neuropathy will cause lower leg dysesthesias that are prominent at night when the individual is supine.
