Practice Essentials
Lumbosacral plexopathy can result in loss of strength and sensation in the regions innervated by the femoral and obturator nerves (lumbar plexopathy) and those reached by the gluteal, peroneal, and tibial nerves (sacral plexopathy). [1] The causes of lumbosacral plexopathy include radiation, which can damage the lumbosacral plexus when directed toward management of abdominal and pelvic malignancies. The diagnosis of radiation plexopathy can be supported by diagnostic studies, such as computed tomography (CT) scanning and magnetic resonance imaging (MRI) of the pelvis. Treatment is symptomatic.
Anatomically, the lumbosacral plexus consists of lumbar (L1-L4) and sacral (L5-S5) portions, which are connected by the lumbosacral trunk (L4-L5). The L1-L4 nerve roots transverse through the psoas muscle and then coalesce into the lumbar plexus, which then divides into anterior and posterior divisions. The first three nerves (iliohypogastric, ilioinguinal, and femoral) of the seven major branches of lumbar plexus provide motor and sensory innervation to the abdominal wall. The next three nerves (lateral femoral cutaneous, femoral, and obturator) innervate the anteromedial thigh. The femoral nerve terminates in the saphenous nerve providing sensation along the medial aspect of the leg.
The sacral plexus also divides into anterior and posterior divisions, which further divide into various peripheral nerves, providing sensory motor innervation to posterior hip girdle, thigh, and anterior and posterior leg. The 5 main nerves are the superior gluteal, inferior gluteal, posterior femoral cutaneous, sciatic, and pudendal. The sciatic nerve divides into the common peroneal and tibial nerves in the thigh.
Although radiation-induced lumbosacral plexopathy is rare, its occurrence is believed to be increasing due to improvements in long-term cancer survival. [2]
Signs and symptoms of radiation-induced lumbosacral plexopathy
In radiation-induced lumbosacral plexopathy, motor deficits in the lower extremities commonly are bilateral (80%) and asymmetrical. Diffuse limb weakness with distal predominance in L5-S1 distribution is relatively common (55% of patients).
Deep tendon reflexes (DTRs) almost always are abnormal at the knees and/or ankles and usually are present bilaterally.
Sensory impairments are present in most patients (75%) and more often are bilateral. Skin changes may be present in areas of radiation portals.
Workup in radiation-induced lumbosacral plexopathy
The diagnosis of radiation plexopathy can be supported by diagnostic studies, such as computed tomography (CT) scanning and magnetic resonance imaging (MRI) of the pelvis. MRI is more sensitive than is CT scanning in detecting tumor recurrence. [3, 4] In addition, positron emission tomography (PET) scanning with 2-[fluorine-18]-fluoro-2-deoxy-D-glucose (FDG) may be helpful in diagnosing recurrent tumor. Electromyography (EMG) reveals myokymic discharges in most patients (57%) with radiation-induced lumbosacral plexopathy.
Management of radiation-induced lumbosacral plexopathy
Treatment of radiation plexopathy is symptomatic. For issues of pain, consider the use of nonopiate pharmacologic medications, such as tricyclic antidepressants or antiepileptic agents (eg, gabapentin, carbamazepine). The use of steroids and opiates, including methadone, can also be assessed.
Strengthening of lower extremity muscles, use of assistive devices for ambulation (eg, cane, walker), and gait training should be prescribed for patients with weakness and proprioceptive feedback loss. Use of orthotics also may be beneficial in certain individuals with lumbosacral plexopathy.
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Pathophysiology
The effects of radiation are correlated with the dose, technique, and concomitant use of chemotherapy. [5] Risk particularly increases with intracavitary radiation. [6] The mechanism may be related to a combination of localized ischemia and subsequent soft-tissue fibrosis due to microvascular insufficiency. With doses above 1000 cGy, pathologic changes can be seen in Schwann cells, endoneurial fibroblasts, vascular cells, and perineural cells. Injury to anterior and posterior nerve roots in rodents has been shown with doses of 3500 Gy. However, combined modality therapy may alter predicted tolerability and potential for late effects.
Radiation-induced lumbosacral plexopathy is particularly noted with uterine, cervical, ovarian, rectal, and testicular cancers, as well as with lymphomas. [7, 8]
Epidemiology
Frequency
United States
Radiation-induced lumbosacral plexopathy is rare (0.3-1.3% of patients treated with radiation). It was noted in 1.3% of patients after abdominal irradiation and in 0.32% of patients after pelvic irradiation.
International
The international incidence of radiation-induced lumbosacral plexopathy is unknown.
Mortality/Morbidity
Generally, the symptoms of radiation-induced lumbosacral plexopathy progress gradually and with variable rapidity. Clinical manifestations of the condition have appeared 3 months to 22 years after the completion of radiation therapy. [9] Jaeckle and colleagues found that 20% of patients developed moderate or even severe weakness over 6 months. [10] Others were found to have mild weakness at 4-5 years following the onset of neurologic symptoms.
Race
No race predilection for radiation-induced lumbosacral plexopathy has been reported.
Sex
The male-to-female ratio is 1:1.2.
Age
Age at the time of presentation ranges from 34-68 years, with a median age of 47.5 years.
