An unusual lumbosacral plexus neuritis (Wartenberg plexitis, see Evans et al) is a unilateral (occasionally bilateral) disorder akin to brachial neuritis, which may cause sciatica, as does occasionally nerve infarction or damage from diabetes, herpes zoster, or a retroperitoneal mass (see Chap. 43).
In the lumbar region, osteoarthritic and related degenerative changes, which together cause a spondylotic narrowing of the canal, lead to compression of one or more lumbar and sacral roots. The problem is more likely to occur if there is a congenitally narrow lumbar canal. The roots are typically compressed between the posterior surface of the vertebral body anteriorly, the facet joint laterally, and the ligamentum flavum posteriorly. Lateral recess stenosis, which is a common feature of spondylotic change (as mentioned above in relation to disc disease), also contributes to root compression and may be the main cause of compression in some patients. Even slight subluxation (spondylolistheses, as discussed below) may also contribute to the stenosis in the anteroposterior dimension. Later, the canal is also narrowed from side to side (reduced interpedicular distance).
The typical features are of fluctuating aching and sharp pain in the low back, buttock and sciatic distribution, occasionally including femoral areas, and generally elicited by prolonged sitting, standing, or walking and relieved by rest. Some patients have virtually constant pain in these areas but still have relief with rest in one or another body position.
In a distinctive presentation that occurs in some cases of lumbar stenosis, termed “neurogenic claudication,” standing or walking causes a gradual onset of numbness and weakness of the legs, usually with asymmetrical sciatic, calf, or buttock discomfort that forces the patient to sit down. When the condition is more severe, the patient gains relief by squatting or lying with the legs flexed at the hips and knees. Often the numbness begins in one leg, spreads to the other, and ascends as standing or walking continues. The ankle tendon reflexes may disappear after walking a distance, only to return on flexing the spine. Pain in the low back and glutei is variable. Disturbances of micturition and impotence are infrequent unless there has been an additional more acute disc herniation. In some patients with lumbar stenosis, neurologic symptoms persist without relation to body position. The process is distinguished from vascular claudication of the legs by its appearance in the standing position, the prominence of numbness in some cases, relief by bending forward at the waist and elongating the lumbar spine, and, of course, by the preservation of distal leg pulses and loss of ankle reflexes. This “claudication of the cauda equina” was known to Dejerine and described by van Gelderen in 1948, and it was shown by Verbiest to be caused not by ischemia but by encroachment on the cauda, for which reason his name has been attached to the claudication syndrome.