Central Canal Stenosis vs Lateral Stenosis

•Usually do not develop symptoms of neurogenic claudication (11)

•Typically have radicular symptoms in a specific dermatomal pattern

•Often have pain at rest, at night, and with the Valsalva maneuver

•Tend to be younger (mean age 41 years) than patients with central canal stenosis (mean age 65 years) (11)

Differential Diagnosis
In older patients with back or leg pain, diagnostic possibilities differ from those in younger patients; nonmechanical causes of back pain such as malignancy, infection, or abdominal aortic aneurysm are more common in elderly patients than in younger patients (12,13).

Malignancy. Red flags that should raise the suspicion of underlying malignancy include significant weight loss, intractable night pain unrelieved by change in posture or pain medicine, or history of malignancy (14).

Infection. Fever with localized back tenderness, recent systemic infection, or history of an invasive spinal procedure should raise the possibility of a spinal infection (13).

Vascular claudication. When evaluating leg pain in the elderly, neurogenic claudication must be distinguished from vascular claudication (Table 2).

Peripheral neuropathy may also superficially mimic features of spinal stenosis. However, patients with peripheral neuropathy usually have a stocking-glove distribution of pain or paresthesia. There may be a bilateral symmetrical reflex loss. Vibratory sensation is frequently diminished (4). Numbness is typically constant with peripheral neuropathy.

Hip disease may produce gait difficulty and leg symptoms. A careful examination of the hips and surrounding soft tissue should be done to exclude significant hip arthritis and gluteal or trochanteric bursitis.

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Table 2
Findings in neurogenic claudication and vascular claudication

Finding	Neurogenic Claudication	Vascular Claudication
Symptoms with walking	Yes	Yes
Symptoms with standing	Yes	No
Variable walking distance before symptoms	Yes	No
Relief with flexion	Yes	No
Relief with sitting	Yes	Yes
Peripheral pulses diminished	No	Yes

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Diagnostic Studies
The diagnosis of lumbar canal stenosis is based on the clinical history and findings on physical examination. Spinal imaging is performed to confirm the clinically suspected diagnosis.

Unless you suspect an underlying systemic illness such as malignancy or infection or are concerned about vertebral compression fracture, imaging is not recommended at the initial visit. In the absence of red flags, imaging should be delayed until the patient has completed a conservative treatment program and when surgical intervention is under consideration.

A reason for this recommendation is that even many people with no symptoms whatsoever have abnormal findings-including spinal stenosis-on imaging studies (15,16). In a study of patients age 60 and older who did not have back pain, radicular pain, or neurogenic claudication, magnetic resonance imaging (MRI) was abnormal in 57% of cases, 36% of scans demonstrated disc herniation, and 21% demonstrated spinal stenosis (16).

A plain radiograph may be helpful. A weight-bearing anterior-posterior and lateral film of the lumbar spine is recommended. Although plain radiographs cannot assess the presence or absence of neural compression, they can show evidence of degenerative changes such as disc degeneration and facet hypertrophy, which are suggestive. They may also reveal spondylolisthesis, instability, scoliosis, a vertebral fracture, or other spinal deformities that may contribute to symptoms.

Nevertheless, advanced radiographic studies such as MRI, computed tomography (CT), and myelography for spinal stenosis remain important diagnostic tools. Modic et al (17) compared the sensitivity of MRI, CT, and myelography in surgically confirmed spinal stenosis. The sensitivity of MRI and CT were similar; myelography alone, without subsequent CT imaging, was the least sensitive. When imaging is required, MRI is the first choice, as it is the least invasive and provides excellent neural and soft tissue resolution. When MRI is not possible or feasible, myelography followed by CT (myelo-CT) is preferred.

In most circumstances, an electromyogram/ nerve conduction study is unnecessary to confirm a clinical diagnosis of radiculopathy due to canal stenosis. This test is most useful if the history and examination are somewhat atypical or if there is suspicion of peripheral neuropathy.

Natural History is Usually Benign
Data on the natural history of lumbar canal stenosis are limited. Anecdotally, the clinical course varies considerably. In most patients, the course is chronic and benign (18,19) A study of 31 patients with spinal stenosis followed for a mean of 49 months found that symptoms remained unchanged in 70%, improved in 15%, and worsened in 15% (19).

Cauda equina syndrome, defined as compression of the lumbar nerves in the central canal causing sensory and motor deficit, saddle anesthesia, and bowel and bladder dysfunction, is rare. It occurs in the setting of a massive central disc herniation or a burst fracture with retropulsion of fragments, or very rarely as a complication of spinal stenosis surgery (20). It may also occur in moderate stenosis with a superimposed herniated disc.