The lumbar plexus may be compressed by an aortic atherosclerotic aneurysm. Usually there is pain that radiates to the hip, the anterior thigh, and occasionally the flank. Slight weakness in hip flexion and altered sensation over the anterior thigh are found on examination. Plexus involvement with tumors is commonplace and presents special difficulties in diagnosis. Carcinoma of either the cervix or prostate may seed along the perineurial lymphatics and cause pain in the groin, thigh, knee, or back without much in the way of sensory, motor, or reflex loss. The pain is more often unilateral than bilateral. The CSF and spinal canal (by MRI) are normal. Testicular, uterine, ovarian, and colonic tumors or retroperitoneal lymphomas, by extending along the paravertebral gutter, implicate various parts of the lumbosacral plexus. Instances of endometriosis that involve the plexus have also been reported, in which case pain fluctuates in parallel with the menstrual cycle (a similar condition exists that implicates only the sciatic nerve). The neurologic symptoms are projected at a distance in the leg and may or may not be confined to the territory of any one nerve. Pelvic and rectal examinations may be negative, and CT scanning and MRI may be necessary to show such lesions. If all these examinations are negative, exploratory laparotomy may have to be undertaken.
In cancer patients, it is sometimes difficult to distinguish the effects of radiation on the lumbosacral plexus from those of metastatic tumor, as is the case in relation to the brachial plexus. Again, the earliest symptom in metastatic lumbosacral plexopathy is usually pain, whereas in radiation plexopathy it is weakness (Thomas et al). Plexopathy from metastatic tumor is usually unilateral and detectable by CT scanning; radiation plexopathy is as often bilateral and changes are not evident in CT or MRI scans. Fasciculations and myokymia are more likely to be seen in patients with radiation plexopathy, which seemingly occurs more frequently in patients with diabetic neuropathy.
Sarcoidosis is another cause and may be responsive to corticosteroids.
Reference has already been made to femoral nerve injury during parturition, but other puerperal complications are also observed. Back pain in the latter part of pregnancy is, of course, common, but there are instances in which the patient complains of severe pain in the back of one or both thighs during labor and after delivery has numbness and weakness of the leg muscles with diminished ankle jerks. Parturitional lumbosacral plexus injuries occur with a frequency of 1 per 2,000 deliveries. This injury is usually unilateral and is manifest by pain in the thigh and leg and symptoms and signs of involvement of the superior gluteal and sciatic nerves (Feasby et al). The attribution of these symptoms to pressure of the fetal head on the sacral plexus(es) is conjectural. A limited plexopathy, occurring after difficult vaginal delivery, mainly impairs sensation in the perineum and sphincteric function (Ismael et al). The perineal muscles may show signs of denervation. Protrusion of an intervertebral disc may also occur during delivery and simulate plexus injury.